Normal Thyroid Hormone Levels – Endocrine Surgery

What is thyroid hormone?

Thyroid hormone is made by the thyroid gland, a butterfly-shaped endocrine gland normally located in the lower front of the neck. Thyroid hormone is released into the blood where it is carried to all the tissues in the body. It helps the body use energy, stay warm and keeps the brain, heart, muscles, and other organs working as they should.

Thyroid hormone exists in two main forms: thyroxine (T4) and triiodothyronine (T3). T4 is the primary form of thyroid hormone circulating in the blood (about 95%). To exert its effects, T4 is converted to T3 by the removal of an iodine atom; this occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. T3 normally accounts for about 5% of thyroid hormone circulating in the blood.

Most thyroid hormone in the blood is bound by protein, while only a small fraction is “free” to enter tissues and have a biologic effect. Thyroid tests may measure total (protein bound and free) or free hormone levels.

Production of thyroid hormone by the thyroid gland is controlled by the pituitary, another endocrine gland in the brain. The pituitary releases Thyroid Stimulating Hormone (abbreviated TSH) into the blood to stimulate the thyroid to make more thyroid hormone. The amount of TSH that the pituitary sends into the bloodstream depends on the amount of thyroid hormone in the body. Like a thermostat, if the pituitary senses low thyroid hormone, then it produces more TSH to tell the thyroid gland to produce more. Once the T4 in the bloodstream goes above a certain level, the pituitary’s production of TSH is shut off. In this way, the pituitary senses and controls thyroid gland production of thyroid hormone. Endocrinologists use a combination of thyroid hormone and TSH testing to understand thyroid hormone levels in the body.

What is a TSH test?

Thyroid tests
Blood tests to measure low or high TSH levels are readily available and widely used. Not all thyroid tests are useful in all situations.

TSH Test
The best way to initially test thyroid function is to measure the TSH (Thyroid Stimulating Hormone) level in a blood sample. Changes in TSH can serve as an “early warning system” — often occurring before the actual level of thyroid hormones in the body becomes too high or too low.

A high TSH level indicates that the thyroid gland is not making enough thyroid hormone (primary hypothyroidism). On the other hand, a low TSH level usually indicates that the thyroid is producing too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (central hypothyroidism). In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.

What is a T4 test?

T4 Tests
A Total T4 test measures the bound and free thyroxine (T4) hormone in the blood. A Free T4 measures what is not bound and able to freely enter and affect the body tissues.

What does it mean if T4 levels are abnormal?
Importantly, Total T4 levels are affected by medications and medical conditions that change thyroid hormone binding proteins. Estrogen, oral contraceptive pills, pregnancy, liver disease, and hepatitis C virus infection are common causes of increased thyroid hormone binding proteins and will result in a high Total T4. Testosterone or androgens and anabolic steroids are common causes of decreased thyroid hormone binding proteins and will result in a low Total T4.

In some circumstances, like pregnancy, a person may have normal thyroid function but Total T4 levels outside of the normal reference range. Tests measuring free T4 – either a free T4 (FT4) or free T4 index (FTI) – may more accurately reflect how the thyroid gland is functioning in these circumstances. An endocrinologist can determine when thyroid disease is present in the context of abnormal thyroid binding proteins.

What is a T3 test?

T3 Tests
T3 tests measure triiodothyronine (T3) levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity.

In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves’ disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 (active form) resulting in a lower proportion of T3.

T3 levels fall late during hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.

Measurement of Free T3 is possible but is often not reliable and therefore may not be helpful.

What is a normal thyroid (hormone) level?

To assess thyroid hormone status for low or high TSH levels we use TSH and FT4 tests. The normal value for a laboratory test is determined by measuring the hormone in a large population of healthy individuals and finding the normal reference range. Normal ranges for thyroid tests may vary slightly among different laboratories, and typical ranges for common tests are given below.

TSH normal values are 0.5 to 5.0 mIU/L. Pregnancy, a history of thyroid cancer, history of pituitary gland disease, and older age are some situations when TSH is optimally maintained in a different range as guided by an endocrinologist.

FT4 normal values are 0.7 to 1.9ng/dL. Individuals taking medications that modify thyroid hormone metabolism and those with a history of thyroid cancer or pituitary disease may be optimally managed with a different normal FT4 range.

Total T4 and Total T3 levels measure bound and free thyroid hormone in the blood. These levels are influenced by many factors that affect protein levels in the body, including medications, sex hormones, and liver disease.
A normal Total T4 level in adults ranges from 5.0 to 12.0μg/dL.
A normal Total T3 level in adults ranges from 80-220 ng/dL.

Free T3 assays are often unreliable and not routinely used to assess thyroid function.

What does it mean if my thyroid levels are abnormal?

Patterns of thyroid tests associated with thyroid disease

Primary Hypothyroidism
A high TSH and low thyroid hormone level (e. g. low FT4) can indicate primary hypothyroidism. Primary hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. Symptoms of hypothyroidism can include feeling cold, constipation, weight gain, slowed thinking, and decreased energy.
Causes of primary hypothyroidism include:

• Autoimmune thyroid disease, including Hashimoto’s thyroiditis
• Thyroid gland dysfunction due to a medication (e.g. amiodarone, tyrosine kinase inhibitors, or cancer immunotherapy)
• Removal of all or part of the thyroid gland
• Radiation injury to the thyroid (e.g. external beam radiation, radioactive iodine ablation treatment)
• Excess treatment with anti-thyroid medications (e.g. methimazole, propylthiouracil)

Early or mild hypothyroidism may present as a persistently high TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.

It is important to remember that normal TSH levels in older individuals (ages 70 and above) are higher than the normal ranges for younger individuals.

Primary Hyperthyroidism
A low TSH and a high thyroid hormone level (e.g. high FT4) can indicate primary hyperthyroidism. Primary hyperthyroidism occurs when the thyroid gland makes or releases too much thyroid hormone. Symptoms of hyperthyroidism can include tremors, palpitations, restlessness, feeling too warm, frequent bowel movements, disrupted sleep, and unintentional weight loss.
Causes of primary hyperthyroidism include:

• Graves’ disease
• Toxic or autonomously functioning thyroid nodule
• Multinodular goiter
• Thyroid inflammation (called thyroiditis) early in the course of disease
• Thyroid gland dysfunction due to a medication (e.g. amiodarone or cancer immunotherapy)
• Excess thyroid hormone therapy

Early or mild hyperthyroidism may present as a persistently low TSH and a normal FT4 hormone level. This pattern is called subclinical hyperthyroidism and your doctor may recommend treatment. Over time, untreated subclinical hyperthyroidism can worsen osteoporosis and contribute to abnormal heart rhythms.

Thyroiditis
Thyroid inflammation, also called thyroiditis, causes injury to the thyroid gland and release of thyroid hormone. Individuals with thyroiditis usually have a brief period of hyperthyroidism (low TSH and high FT4 or Total T4) followed by development of hypothyroidism (high TSH and low FT4 or Total T4) or resolution.

Some forms of thyroiditis are transient, like post-partum thyroiditis or thyroiditis following an infection, and often resolve on their own without need for medication.

Other forms of thyroiditis, like thyroiditis resulting from cancer immunotherapy, interferon alpha, or tyrosine kinase inhibitors, usually result in permanent hypothyroidism and require long term treatment with thyroid hormone replacement.

Your endocrinologist will monitor your thyroid tests during thyroiditis and can help determine if you need short- and long-term medications to balance your thyroid function and control any symptoms.

Central Hypothyroidism
A low TSH and a low FT4 may indicate pituitary disease. Detection of central hypothyroidism should prompt your doctor to check for problems in other pituitary hormones, an underlying cause, and you may need imaging tests to look at the pituitary gland.

Central hypothyroidism is treated with thyroid hormone replacement. Importantly, adequacy of thyroid replacement in central hyperthyroidism is assessed with FT4 and Total T4 tests not TSH as in primary hyperthyroidism, and deficiency in stress hormone cortisol should be assessed before starting thyroid treatment to prevent an adrenal crisis. 

Causes of central hypothyroidism include pituitary gland disease, such as a pituitary mass or tumor, history of pituitary surgery or radiation, pituitary inflammation (called hypophysitis) resulting from autoimmune disease or cancer immunotherapy, and infiltrative diseases.

Rare causes of abnormal thyroid function
Thyroid hormone resistance
Iodine induced hyperthyroidism
TSH-secreting tumor (TSH-oma)
Germ cell tumors
Trophoblastic disease
Infiltrative diseases, such as systemic scleroderma, hemochromatosis, or amyloidosis.

When abnormal thyroid function tests are not due to thyroid disease

While blood tests to measure thyroid hormones and thyroid stimulating hormone (TSH) are widely available, it is important to remember that not all tests are useful in all circumstances and many factors including medications, supplements, and non-thyroid medical conditions can affect thyroid test results. An endocrinologist can help you make sense of thyroid test results when there is a discrepancy between your results and how you feel. A good first step is often to repeat the test and ensure there are no medications that might interfere with the test results. Below are some common reasons for mismatch between thyroid tests and thyroid disease.

Non-thyroidal illness
Significant illness, such as an infection, cancer, heart failure, or kidney disease, or recent recovery from an illness can cause transient changes in the TSH. Fasting or starvation can also cause a low TSH. An endocrinologist can help to interpret changes in thyroid function tests in these circumstances to distinguish non-thyroid illness from true thyroid dysfunction.

Test interference
Biotin, a common supplement for hair and nail growth, interferes with many thyroid function tests and can lead to inaccurate results. Endocrinologists recommend stopping biotin supplements for 3 days before having a blood test for thyroid function.

Individuals who have exposure to mice, like laboratory researchers and veterinarians, may develop antibodies against mouse proteins in their blood. These antibodies cross react with reagents in multiple thyroid function tests and cause unpredictable results. A specialized assay can accurately measure thyroid hormone levels and TSH in this circumstance.

I don’t feel well, but my thyroid tests are normal

Thyroid blood tests are generally accurate and reliable. If you do not have low or high TSH levels and your thyroid tests are normal, your symptoms may not be related to thyroid disease, and you may want to seek additional evaluation with your primary care physician.

How is hypothyroidism treated?

What is thyroid medication?

Thyroid Hormone Treatment
Levothyroxine is the standard of care in thyroid hormone replacement therapy and treatment of hypothyroidism. Levothyroxine (also called LT4) is equivalent to the T4 form of naturally occurring thyroid hormone and is available in generic and brand name forms.

How do I take levothyroxine?
To optimize absorption of your thyroid medication, it should be taken with water at a regular time each day. Multiple medications and supplements decrease absorption of thyroid hormone and should be taken 3–4 hours apart, including calcium and iron supplements, proton pump inhibitors, soy, and multivitamins with minerals. Because of the way levothyroxine is metabolized by the body, your doctor may ask you to take an extra pill or skip a pill on some days of the week. This helps us to fine tune your medication dose for your body and should be guided by an endocrinologist.

For patients with celiac disease (autoimmune disease against gluten) or gluten sensitivity, a gluten free formulation of levothyroxine is available. Some individuals may have genetic variant that affects how the body converts T4 to T3 and these individuals may benefit from the addition of a small dose of triiodothyronine.

Liothyronine is replacement T3 (triiodothyronine) thyroid hormone. This medication has a short half-life and is taken twice per day or in combination with levothyroxine. Liothyronine alone is not used for treatment of hypothyroidism long term.

Other formulations of thyroid hormone replacement include natural or desiccated thyroid hormone extracts from animal sources. Natural or desiccated thyroid extract preparations have greater variability in the dose of thyroid hormone between batches and imbalanced ratios if T4 vs T3. Natural or animal sources of thyroid hormone typically contain 75% T4 and 25% T3, compared to the normal human balance of 95% T4 and 5% T3. Treatment with a correct balance of T4 and T3 is important to replicate normal thyroid function and prevent adverse effects of excess T3, including osteoporosis, heart problems, and mood and sleep disturbance. An endocrinologist can evaluate symptoms and thyroid tests to help balance thyroid hormone medications.

How do I know if my thyroid dose is correct?

Monitoring thyroid levels on medication
Correct dosing of thyroid hormone is usually assessed using the same tests for diagnosis of thyroid disease, including TSH and FT4. Thyroid tests are typically checked every 4-6 weeks initially and then every 6 to 12 months once stable. In special circumstances, such as pregnancy, a history of thyroid cancer, central hypothyroidism, amiodarone therapy, or use of combination T4 and T3 thyroid hormone replacement, your endocrinologist may check different thyroid tests. Additionally, your endocrinologist will evaluate for symptoms of hyperthyroidism and hypothyroidism and perform a physical exam.

Women who are pregnant and women who may become pregnant should only be treated with levothyroxine (T4). Only T4 efficiently crosses the placenta to provide thyroid hormone to the developing fetus. Thyroid hormone is critical in early pregnancy for brain development. Normal ranges for thyroid tests in pregnancy are different and change by trimester. Women with thyroid disease in pregnancy or who are considering pregnancy should be under the care of an endocrinologist to guide therapy.

Individuals with a history of thyroid cancer, even if only a portion of the thyroid was removed, also have different target ranges for TSH and FT4 tests. Thyroid hormone replacement in these individuals is closely tied to ongoing thyroid cancer surveillance, monitoring of thyroid cancer tumor markers, and dynamic assessment of recurrence risk. These patients are optimally managed by a multidisciplinary team including an endocrinologist and endocrine surgeon.

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Low to high ranges, symptoms, and what they mean

The thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood. TSH levels convey how well a person’s thyroid is functioning.

Doctors can use TSH test results to diagnose thyroid disorders, such as hypothyroidism and hyperthyroidism.

The pituitary gland produces TSH, which is a hormone that stimulates the thyroid gland.

The thyroid is a butterfly-shaped gland in the throat. It produces hormones that help regulate many bodily functions, such as metabolism, heart rate, and body temperature.

This article describes the TSH test and results. We also discuss what high and low TSH levels indicate and available treatments.

Share on PinterestMNT-infographic_guide infographic by Diego Sabogal 1401179-TSH-levels-original

The normal range depends on a person’s age and whether they are pregnant.

The ranges tend to increase as a person gets older. Research has not shown a consistent difference in TSH levels between males and females.

However, according to the American Thyroid Association, doctors generally consider levels are within a normal range between 0.4–4.0 milliunits per liter (mU/l).

The following table provides estimates of TSH levels that are normal, low (indicating hyperthyroidism), and high (indicating hypothyroidism):

Many labs use these reference values.

However, there is some debate about these ranges. The author of a 2016 review suggests that normal levels are more likely to fall between 0.5–2.5 milli-international units (mIU) per milliliter.

Females are more likely to experience thyroid dysfunction than males. The Office on Women’s Health reports that 1 in 8 females experience thyroid problems at some point. This includes hyperthyroidism and hypothyroidism. The risk of thyroid problems increases during pregnancy and around menopause.

Research does not show a consistent difference in TSH levels between males and females. However, some evidence suggests that TSH levels are generally higher in females. For example, studies in 2020 investigating Chinese and French populations suggest that TSH levels are higher in females, but other factors, such as age, are more likely to affect TSH levels.

In some people, thyroid conditions are linked with sexual dysfunction. This may affect more males than females. According to a 2019 study, 59–63% of males with hypothyroidism also experience sexual dysfunction, compared with 22–46% of females who have hypothyroidism.

Blood TSH levels tend to increase as people get older, with evidence noting that hypothyroidism is the most common thyroid condition in people over 60 and steadily increases with age.

Research involving older adults suggests that roughly 7–14% of people may have TSH levels above the upper limit of reference ranges.

Pregnancy hormones naturally increase the levels of certain thyroid hormones in the blood. This is essential for the development of the fetal brain and nervous system.

At the same time, the levels of TSH in the blood decrease. As a result, doctors use lower reference ranges during pregnancy. The lower TSH range is decreased by around 0.4 mU/l, and the upper limit reduced by approximately 0.5 mU/l.

Levels of TSH in the blood increase gradually during the second and third trimesters, but they remain lower than normal levels in women who are not pregnant.

Doctors carefully monitor TSH levels throughout pregnancy. Having unusually high or low levels can affect the risk of miscarriage and cause pregnancy-related complications, such as:

• preeclampsia
• premature birth
• low birth weight
• congestive heart failure

TSH levels are highest at birth and gradually decrease as a child gets older. As such, TSH levels can vary among children. After the newborn phase, health experts may define mild hypothyroidism in children as TSH levels ranging between 4.5–10 mU/l.

The following table shows TSH levels for children by age, according to an older study using data from 512 healthy children:

High TSH levels indicate hypothyroidism. People develop hypothyroidism when their thyroid produces low levels of hormones.

When someone’s thyroid gland does not produce enough hormones, the pituitary gland produces more TSH to compensate.

Symptoms of hypothyroidism may include:

• fatigue
• weight gain
• swelling of the face and neck
• increased sensitivity to cold temperatures
• dry skin
• thinning hair
• a slow heart rate
• irregular or heavy menstrual periods
• fertility problems
• depression
• constipation

Low TSH levels indicate hyperthyroidism. This is also known as an overactive thyroid.

If a person’s thyroid gland is secreting levels of hormones that are too high, the pituitary gland produces less TSH.

Symptoms of hyperthyroidism can include:

• irregular or rapid heartbeat
• muscle weakness
• nervousness or irritability
• difficulty sleeping
• frequent bowel movements or diarrhea
• weight loss
• mood changes

The TSH test involves a healthcare professional drawing blood from a vein in the inner arm. They then send the blood sample for laboratory testing.

Usually, people do not need to prepare for a TSH test. However, if the doctor is checking the blood for more than one issue, a person may need to fast or prepare in another way. The doctor will provide this information beforehand.

A TSH test is often the best way to monitor thyroid function. However, if a person has abnormally high or low TSH levels, the doctor may need to perform at least one other diagnostic test to identify the underlying cause. These tests look at levels of specific thyroid hormones and antibodies.

In addition to age, sex, and pregnancy, many other factors can also affect TSH levels. Evidence suggests that genetic, environmental, or intrinsic factors can alter TSH levels. Some of these factors may include:

• other conditions occurring at the same time
• medications
• supplements
• ethnicity
• diet and iodine status
• time of day and time of year
• autoantibodies and heterophilic antibodies
• smoking
• pollutants

Doctors can treat hypothyroidism with medications, such as levothyroxine, that replace the missing thyroid hormones.

A person should take this medication once a day or as prescribed. The doctor will monitor how well the treatment is working by running additional blood tests every few months.

According to the Food and Drug Administration (FDA), people should take levothyroxine once a day: in the morning and on an empty stomach, at least half an hour before eating.

The FDA also recommends that a person informs their doctor if they eat soybean flour, walnuts, dietary fiber, or cottonseed meal — these foods can affect how the body processes levothyroxine. Drinking grapefruit juice may also delay the absorption of levothyroxine.

Hyperthyroidism treatments focus on reducing thyroid hormone levels to prevent long-term health complications.

A person may need to take beta-blockers and antithyroid medications.

Another effective treatment is radioiodine therapy. This involves taking a capsule or liquid that contains radioactive iodine-131, which destroys cells that produce thyroid hormones. However, people who take radioiodine therapy may develop hypothyroidism in the future.

Surgical removal of the thyroid gland can treat severe hyperthyroidism. Doctors often reserve this for individuals who cannot take first-line medications and severe cases of hyperthyroidism.

A TSH test measures the amount of the hormone in the blood. Doctors can use the results to diagnose thyroid conditions, such as hypothyroidism and hyperthyroidism.

Normal TSH ranges can vary widely, depending on a person’s age, sex, and weight. Reference TSH ranges remain controversial, but for most people, the normal range falls between 0.4 and 4.0 mU/l.

Having an overactive or underactive thyroid can cause health issues that interfere with a person’s daily life. During pregnancy, unusually high or low TSH levels can lead to complications.

A doctor can provide more information about the TSH test and interpreting the results.

When tsh analysis is high | Echo of Cairo

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When parsing is high

When is TSH analysis high? A question that interests many people, since the thyroid gland can be affected by some diseases, with high or low levels of its hormones, and TSH is a thyroid stimulating hormone that is secreted by the pituitary gland to stimulate the thyroid gland to perform various functions in the body, therefore we will show you in this article what it means that tsh analysis is high and what is on site Echo of Cairo .

What is the TSH hormone?

• TSH is a hormone responsible for the activity of the thyroid gland, so it can be used in tests that determine the level of thyroid activity in a person.
• This test is a sure way to check your thyroid levels and determine if you have hypothyroidism or overactivity.
• The TSH test is used as an effective thyroid monitoring tool.

Normal levels of the hormone TSH

• Normal levels of the hormone in adults range from 5 to 5 milliliters per liter.
• If the result of the analysis indicates an increase in the level of the hormone above the norm, this indicates the presence of hypothyroidism or problems and tumors of the pituitary gland.
• If the result of the analysis shows that the level of the hormone is less than normal, this indicates an increase in the activity of the thyroid gland or the presence of pregnancy.
• This can sometimes happen to patients who have thyroid problems due to medications they are taking, and it can cause symptoms of hyperthyroidism.
• There are studies that show that drugs containing lithium, dopamine and others can affect the level of TSH in the blood.

Thyroid test msh

• This is a test that is carried out in a medical laboratory and at the request of a doctor to determine the condition of the thyroid gland, since any deficiency or increase above the norm leads to many pathological symptoms.
• After reviewing the results of this hormone test, if there is any abnormality in the functioning of the thyroid gland, medical intervention is necessary by taking appropriate drugs or performing surgery if necessary.

The thyroid gland and its functions

• The thyroid gland is one of the endocrine glands, and the hormones it secretes circulate directly in the blood, and the thyroid gland is the largest endocrine gland in the human body.
• It is similar in structure to a butterfly and consists of two parts, and its place in the human body is the neck in front of the trachea.
• The main role of the thyroid gland in the body is the secretion of a group of hormones such as T3 and T4.
• These hormones regulate vital functions in the human body, such as growth and metabolism, as well as any imbalance that occurs in the thyroid gland, and cause the secretion of these hormones to increase or decrease above normal levels, causing an imbalance in various vital functions. in the human body.

Thyroid and TSH test for hormones

• Now we will ask about the relationship of the thyroid gland and the test for this hormone, how to read a normal TSH test, high or low, and what these results say.
• The doctor asks the patient to do this test, and when he suspects that something is wrong with the thyroid gland, he asks for the hormone TSH, which is secreted by the pituitary gland.
• The task of this hormone is to stimulate the thyroid gland to release its hormones into the blood so that the body can carry out its vital functions.
• Because TSH controls the amount of thyroid hormone secretion, these secretions can increase or decrease, causing an imbalance in thyroid hormone secretion.
• When the hormones T3 and T4 secreted by the thyroid gland decrease, the pituitary gland secretes TSH to maintain the thyroid gland and processes it to increase the secretion of these deficient hormones into the blood so that the body can carry out its vital functions.
• In the case of increased secretion of the hormones T3 and T4 into the blood, this occurs due to an increase in TSH, which is secreted by the pituitary gland.
• Every defect that occurs in the secretion of these hormones must be treated, and its diagnosis depends on the diagnosis of the defect and its treatment according to the type of defect, treatment with the appropriate hormone, and knowledge of the gland in which the defect is located.
• If there is an excess or decrease in the secretion of hormones as a result of a problem and defect in the functioning of the thyroid gland, the defect in this case is called the first defect.
• If the defect in the secretion of previous hormones is caused by a problem with the pituitary gland, this is called a secondary imbalance.

Also read: Residence permit requests and how to renew it

Read normal thyroid tsh test or low or high to determine the defect, its location and method of treatment.

But if T3 and T4 levels are elevated and TSH levels are also elevated, the diagnosis is an increase in secondary thyroid function.

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Server load: identify causes

The virtual machine does not always run at the expected speed. The site suddenly starts to slow down, the scripts take a long time to complete. In this article, we will show how you can analyze the performance of a virtual machine and find the causes of slowdowns in work.

Our focus will be on CPU and HDD usage.

• top 9 team0020
• Average system load (load average)
• Cpu parameter
• CPU load (parameters sy, us, ni)
• Overselling definition (parameter st)
• I/O load (wa parameter)
• I/O load: digging deeper (atop)
• Conclusion

Let’s try to answer the question: what to do in case of problems on the server, what tools to use and what to look for to diagnose performance problems in the operating system Linux .

The top command

The top command will be the main tool in this matter. The result of its execution looks like this:

The program top gives a dynamic view of the running system in real time. The upper part of the output is occupied by a brief generalized information, the lower part is a list of running processes.

Consider the main indicators that may be of interest to us.

Average system load (load average)

Load Average is the average value of system load over a period of time (hereinafter LA). Three values ​​show the average load over the last 1, 5 and 15 minutes. LA is one of the most controversial indicators. You can find many conflicting articles on what value is considered normal. It is generally accepted that a value of 0 is a idle core, and a value of 1 is a full core load. You can only estimate the average load indicator by knowing the number of cores in the system. You can find out how many cores are available with the command:

dmidecode -t processor | grep "Core Enabled:"
Core Enabled: 6
Core Enabled: 6
 

We see that this system has 12 physical cores (6+6). Accordingly, the normal LA value should be less than 12. However, Intel processors use Hyper-Threading technology, which divides one physical core into two logical ones.

dmidecode -t processor | grep "Thread Count:"
Thread Count: 12
Thread Count: 12 

Accordingly, in this case, the system can simultaneously have 24 virtual processors (threads).

Turbo Boost technology allows the processor to “overclock” and operate at a frequency higher than the declared one (ie, above 100%, above one). What indicator LA is considered normal in this case is the subject of disputes.

There have been attempts to calculate the normal value of LA empirically. But we consider it a pointless exercise. The fact is that LA also includes processes that are in the read / write queue and are not related to the processor, as well as processes with a priority changed using the nice command. If a command is run with a low priority, it will be queued, but will not affect the actual performance.

High LA may indicate some problem. On the other hand, a high value does not necessarily indicate a problem. It is impossible to rely only on LA in diagnostics; its values ​​​​should be taken into account only in conjunction with other values. Therefore, we move on to the next line of interest to us: Cpu .

Cpu parameter

Line Cpu shows several load parameters at once:

us (user)	CPU usage by user processes
sy (system)	CPU usage by system processes
ni (nice)	CPU usage by processes with changed priority with command nice
id (idle)	Idle processor. We can say that these are free resources
wa (IO-wait)	Talks about I/O related downtime
hi (hardware interrupts)	Shows how much CPU time was spent servicing a hardware interrupt
si (software interrupts)	Shows how much CPU time was spent servicing a software interrupt
st (stolen by the hypervisor)	Shows how much CPU time was “stolen” by the hypervisor

We will not delve into the analysis of the values ​​ hi and si in this article, since problems with interrupts are very rare. Let’s just say that the most likely reason for the high values ​​of these parameters is a problem with the code, the kernel, or a DDoS attack.

Let’s take a closer look at the rest of the parameters Сpu .

CPU load (parameters sy, us, ni)

High values ​​ sy , us and ni are the most clear and easy to diagnose, as they show the load on the CPU created by running programs. We look at the output of the command top for the processes in the column %CPU and optimize them if necessary. Or just add CPU power to the server.

However, keep in mind that single-threaded processes will only run on one core. In this case, even with a low total us, problems can be observed.

It should also be added that a high value of ni will not always negatively affect the performance of the server. It is possible that the priority of the processes was lowered on purpose so that they would only run when the processor was free. These processes do not affect the operation of the system. For example, it can be the processes of creating backups.

Example of diagnosing problems at high

us and sy

On server top shows the following values:

CPU: 21.0% user, 0.0% nice, 74.6% system, 0.0% interrupt, 4.4% idle
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
95383 mysql 37 4 0 227M 74388K sbwait 1 0:00 49. 80% mysqld
96904 qhost 1 97 0 171M 31884K CPU1 1 0:04 7.08% httpd
97360 frekbok 1 97 0 185M 42464K RUN 0 0:02 7.08% httpd
97442 frekbok 1 97 0 178M 37196K RUN 2 0:01 5.18% httpd
97423 frekbok 1 -4 0 178M 37160K RUN 1 0:01 4.79% httpd
97439 frekbok 1 97 0 178M 37052K RUN 2 0:01 4.79% httpd
97411 frekbok 1 -4 0 178M 37148K RUN 3 0:01 4.69% httpd
97418 frekbok 1 97 0 178M 37168K RUN 0 0:01 4.59% httpd
97444 frekbok 1 -4 0 178M 37192K RUN 1 0:01 4.59% httpd
97416 frekbok 1 -4 0 178M 37052K RUN 2 0:01 4.49% httpd
97421 frekbok 1 -4 0 178M 37060K CPU0 0 0:01 4.39% httpd
97424 frekbok 1 97 0 178M 37304K RUN 2 0:01 4.30% httpd
 

At the same time, LA is greater than 100.

It is clearly seen that the problems are in the lack of CPU for mysql work, and in a large number of http user connections frekbok .

We go to the user frekbok and look at the log apache . There we see such POST requests, and many similar ones:

76. 164.234.170 - - [18/Sep/2015:06:10:41 +0400] "POST /component/k2/ HTTP/1.0" 200 59 "Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko"
76.164.234.170 - - [18/Sep/2015:06:10:41 +0400] "POST /component/k2/ HTTP/1.0" 200 59"Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko"
76.164.234.170 - - [18/Sep/2015:06:10:43 +0400] "POST /component/k2/ HTTP/1.0" 200 59 "Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko"
 

Based on the analysis of the logs, we can conclude that the problem is in Chinese bots that post ads in comments on the site. We put the captcha on commenting or turn off comments, clean the database. Problem solved.

Overselling definition (parameter st)

Parameter st is interesting for virtual machines. We can say that it displays the CPU overselling on the parent node. It will be different from 0 if the VDS needs a processor, but the hypervisor cannot allocate the CPU because it is currently being used by other VDS. If this parameter takes large values ​​on your VDS (approximately more than 5-10% together with high LA) and this interferes with your work, then all that remains is to write to technical support with a request to transfer VDS to another node.

I/O load (wa parameter)

The most interesting indicator is wa . On modern servers, processor and memory power is usually sufficient, and most of the problems are associated with I / O operations.

High values ​​ wa , as well as high LA, usually indicate idle processes in the state D-state associated with the disk subsystem or network problems. However, we must not forget that this parameter applies to all I / O operations. For example, on a dedicated server, this value may increase when working with a USB drive, waiting for a response from a socket, or be caused by other reasons.

Simplified state model in Linux

• D -state – continuous sleep state (processes that are waiting for an I/O thread to be released)
• R -state – the process is currently active (currently running)
• S -state it is waiting for some event or signal
• T -state – process stopped by STOP signal or executing trace
• Z -state – “zombie”, a process that has completed its execution, but is present in the system to allow the parent process to read its exit code

You can view the status of processes in the system using the ps command with options: ps aux

From practical experience, noticeable problems begin when wa is greater than 10-30%. You need to understand that a large value of this parameter does not always indicate problems. But it is desirable to establish the cause of this behavior and, if possible, correct the situation.

An example of finding the causes of high wa and load average

We look at the command ps aux | grep D processes in state D .

102 628884 0.0 0.0 97308 2432 ? D 13:08 0:00 /usr/sbin/exim4 -bd -q30m
102 628885 0.0 0.0 97308 2432 ? D 13:08 0:00 /usr/sbin/exim4 -bd -q30m
102 628886 0.0 0.0 97308 2432 ? D 13:08 0:00 /usr/sbin/exim4 -bd -q30m
102 628887 0.0 0.0 97308 2424 ? D 13:08 0:00 /usr/sbin/exim4 -bd -q30m
102 628888 0.0 0.0 97308 2424 ? D 13:08 0:00 /usr/sbin/exim4 -bd -q30m
102 628890 0.0 0.0 97308 2424 ? D 13:08 0:00 /usr/sbin/
 

We see that many processes are hanging in the waiting state exim4 . Most likely the server was hacked and spam is being sent from it massively. We stop exim and find the mailing source.

If you have several VDS on a node and you need to find the load source, you need to find the one that sends spam. You can use command 9 for this.0269 tcpdump -n | grep “smtp” , we will use it to analyze mail traffic on port 25 and find the IP address from which spam is being sent.

You need to know that a high wa inside a VDS does not always mean a problem inside the container. Problems are also possible on the “parent” node. For example, it lacks disk I/O for all VDS. Therefore, your processes get into a waiting state. In this case, you need to create a ticket in those support.

I/O load: digging deeper (atop)

A convenient tool for determining load causes is atop with options: atop -l -c -d1

However, the following description will primarily refer to VDS on KVM virtualization and dedicated servers. On OpenVZ virtualization, we will not be able to use the full capabilities of this utility, and most likely you will have to contact those. support.

Consider its output:

In line DSK we see the disk usage at the moment. On line busy as a percentage indicates approximately how many “resources” of the disk are being consumed at the moment. If there is a value of about 100%, then the disk is most likely experiencing problems with I / O operations. In the case of using VDS, this line may not exist and you should not be afraid.

At the bottom we see a list of processes that are currently performing disk operations. At the top of the list will be the processes consuming the most resources.

As we can see, the process with ID pid 539189 is currently actively writing to disk. You can find out to which files this process writes data using the lsof command.

Calling the command lsof -p539189 (substituting the pid identifier of the desired process) showed the following result:

 mysqld 539189 110 4u REG 182.374993 0 12516 (deleted) /tmp/ib30lihW
 lsof: no pwd entry for UID 110
 mysqld 539189 110 5u REG 182.