Decrease in hematocrit: What it is, levels, high and low range
What it is, levels, high and low range
Hematocrit is the percentage of red blood cells in a person’s blood. A typical hematocrit range in healthy adults is 37–52%. This varies depending on a person’s sex and age.
Authors of a 2017 study identified the above typical range.
Low red blood cell levels indicate conditions such as anemia. High red blood cell levels could signal polycythemia, increasing a person’s chance of developing a blood clot.
If a person feels tired, dizzy, or short of breath, a doctor may want to test their hematocrit levels to see if those levels fall into a normal range or not.
Read on to learn more about what this measure of red blood cell volume means, symptoms of abnormal levels, and what low and high levels might indicate.
Hematocrit measures the percentage of red blood cells in the body. For example: if a person has 50 milliliters (ml) of red blood cells in 100 ml of blood, their hematocrit level is 50%.
Red blood cells transport oxygen around the body and give blood its characteristic red color.
In addition to oxygen, they also contain hemoglobin, a protein that binds to oxygen molecules. This allows red blood cells to pick up oxygen from the lungs and deliver it throughout the body.
An adequate amount of red blood cells is essential to keep the body’s processes running smoothly.
Many conditions can affect red blood cell production or its life cycle. This can make it difficult for a medical professional to diagnose these conditions. A doctor will use a hematocrit test to confirm whether a person’s red blood cell count is affecting a health condition.
Doctors usually test hematocrit levels as part of a complete blood count (CBC).
A CBC is composed of a range of tests and may include:
- red blood cell count
- reticulocyte count (young red blood cells)
- an analysis of hemoglobin levels
- an analysis of red blood cells, including size and shape
- white blood cell tests
- platelet tests
A doctor will also consider a person’s sex, race, and age.
It is important to note that certain blood-related conditions, such as sickle-cell anemia, affect particular demographic groups at higher rates.
Learn more about sickle cell anemia in African Americans here.
A doctor may request frequent hematocrit tests to monitor the effect of chemotherapy on a person’s bone marrow.
Both high and low hematocrit levels can be detrimental to a person’s health and result from various conditions and lifestyle factors.
What are normal hematocrit levels?
Different institutions will define normal hematocrit levels differently. However, a 2017 cross-population study found the following ranges to be typical.
- Male: 42-52%
- Female: 37-47%
- Children: 30–44%, depending on their age and sex
Newborn babies have high hematocrit levels that gradually decrease as they get older.
If a person has recently received a blood transfusion, it may affect their results. Additionally, pregnant individuals may have lower levels than usual because the body increases its blood volume during pregnancy.
Other factors, such as smoking and chronic obstructive pulmonary disease (COPD), may push levels into a higher range.
Low levels
A hematocrit level below 35% in women and 41% in men is low. A level under this value can signify chronic anemia.
High levels
Hematocrit levels above the typical ranges can have adverse effects. It may indicate serious underlying health conditions.
Accuracy of results
Results from hematocrit tests are typically accurate and provide a clear reading of a person’s red blood cell levels.
However, the percentage of red blood cells in someone’s blood can change depending on various lifestyle factors and even environmental changes. According to research, red blood cell counts tend to increase at high altitudes.
Exercise, particularly strength training, may also affect hematocrit levels. A 2018 study found that females who participated in 16 weeks of strength exercise had lower levels at the end than when they started.
However, the study had a small sample size of 26 middle-aged, sedentary Turkish women. This means that these findings aren’t necessarily representative of a wider population.
Dehydration can also raise hematocrit levels, so this test is useful if a doctor suspects severe dehydration is the cause of a person’s symptoms.
When a person has low hematocrit levels, they tend to present with the following symptoms:
- pale complexion
- weakness
- fatigue
- low energy
- trouble breathing
- irregular heartbeat
- cold hands or feet
These symptoms also indicate anemia, a condition where hemoglobin levels are lower than normal. Hemoglobin is a protein found in red blood cells that carries oxygen around the body.
Mild anemia is treatable, and it is particularly common in women. Severe anemia could signal a more serious underlying health condition that requires more extensive treatment.
Doctors associate anemia with several health conditions, including:
Nutrient deficiency
A person may lack B12, folate, or iron in their diet.
Learn more about how nutrient deficiency anemia is diagnosed and treated.
Chronic bleeding
This commonly occurs due to digestive tract ulcers, which are sores caused by the bacteria H.pylori or chronic use of anti-inflammatory medications such as ibuprofen, other nonsteroidal anti-inflammatory drugs (NSAIDs), and aspirin. Many women also experience excessive blood loss from heavy menstrual bleeding.
Bone marrow disorder
This includes aplastic anemia, which damages stem cells in bone marrow.
Cancer
These cancers spread to bone marrow, such as leukemia and lymphoma.
Learn more about bone marrow cancers here.
Kidney failure
Kidney disease can lower the production of red blood cells, reducing hematocrit levels.
Thalassemia
When a person has this condition, their body does not produce enough hemoglobin.
Learn more about thalassemia here.
Sickle cell anemia
This condition changes the shape of red blood cells.
These cells die earlier than normal, and they also clump together, which impairs blood flow.
Learn more about sickle cell anemia here.
Autoimmune disease
Conditions like rheumatoid arthritis and lupus may reduce red blood cell count.
Learn more about autoimmune diseases here.
When a person has high hematocrit levels, they tend to present with these symptoms:
- flushed skin
- dizziness
- vision problems
- headaches
- enlarged spleen
These symptoms signal polycythemia, a condition where the body produces too many red blood cells. This means blood is thicker and clots more easily.
Doctors cannot cure polycythemia, so treatment focuses on symptom management. The main goal is to avoid stroke and deep vein thrombosis (DVT), which is a blood clot usually occurring in a deep vein in the leg.
In some cases, dehydration causes polycythemia. When a person does not drink enough, their plasma levels drop, increasing the proportion of red blood cells in their blood volume.
A person can lower their red blood cell count by rehydrating.
Some conditions that can cause high hematocrit levels include:
Lung or pulmonary disease
When the lungs cannot absorb oxygen effectively, and oxygen levels drop, the body compensates by making more red blood cells. One common pulmonary disease causing this is COPD.
Learn more about COPD here.
Heart disease
If the structure of a person’s heart reduces its ability to pump blood around the body, it can no longer sustain vital organs with oxygen. To try and overcome the oxygen deficit, the body produces more red blood cells.
Learn more about heart disease here.
Kidney cancer
Sometimes kidney cancer cells create more erythropoietin. Erythropoietin is a hormone that tells the bone marrow to create more red blood cells.
Learn more about kidney cancer here.
Genetic disease
The JAK2 gene, which controls the number of blood cells made in the bone marrow, can affect certain conditions.
When someone has a mutated JAK2 gene, the body could make a protein that signals the bone marrow to create more red blood cells than it needs.
Learn more about genetic disorders here.
A person should speak with a doctor if they are experiencing any of the symptoms listed above that could be a sign of high or low hematocrit levels, including fatigue, weakness, vision problems, and dizziness.
These symptoms can also indicate an underlying condition, so a person must contact a doctor promptly to prevent future complications.
If a person is receiving chemotherapy treatment, a doctor should perform regular hematocrit tests to monitor bone marrow health.
Hematocrit is the percentage of blood cells in a person’s blood volume. A doctor may test an individual’s hematocrit level due to certain symptoms.
A low hematocrit level means there are too few red blood cells in the body. In these cases, a person may experience symptoms that signal anemia. Common symptoms include fatigue, weakness, and low energy.
If a person has too many red blood cells, they have a high hematocrit level. A person may experience dizziness and headaches, which can be a sign of the condition polycythemia.
Demographic and lifestyle factors can influence a person’s hematocrit levels. For example, males tend to have higher levels than females. Pregnant individuals can experience a decrease in hematocrit levels, and strength training may also reduce levels.
There are also several health conditions that can cause hematocrit levels outside the normal range. Excessive bleeding, thalassemia, and kidney disease are causes of low levels. COPD and sickle cell anemia can cause high levels.
Read this article in Spanish.
What it is, levels, high and low range
Hematocrit is the percentage of red blood cells in a person’s blood. A typical hematocrit range in healthy adults is 37–52%. This varies depending on a person’s sex and age.
Authors of a 2017 study identified the above typical range.
Low red blood cell levels indicate conditions such as anemia. High red blood cell levels could signal polycythemia, increasing a person’s chance of developing a blood clot.
If a person feels tired, dizzy, or short of breath, a doctor may want to test their hematocrit levels to see if those levels fall into a normal range or not.
Read on to learn more about what this measure of red blood cell volume means, symptoms of abnormal levels, and what low and high levels might indicate.
Hematocrit measures the percentage of red blood cells in the body. For example: if a person has 50 milliliters (ml) of red blood cells in 100 ml of blood, their hematocrit level is 50%.
Red blood cells transport oxygen around the body and give blood its characteristic red color. In addition to oxygen, they also contain hemoglobin, a protein that binds to oxygen molecules. This allows red blood cells to pick up oxygen from the lungs and deliver it throughout the body.
An adequate amount of red blood cells is essential to keep the body’s processes running smoothly.
Many conditions can affect red blood cell production or its life cycle. This can make it difficult for a medical professional to diagnose these conditions. A doctor will use a hematocrit test to confirm whether a person’s red blood cell count is affecting a health condition.
Doctors usually test hematocrit levels as part of a complete blood count (CBC).
A CBC is composed of a range of tests and may include:
- red blood cell count
- reticulocyte count (young red blood cells)
- an analysis of hemoglobin levels
- an analysis of red blood cells, including size and shape
- white blood cell tests
- platelet tests
A doctor will also consider a person’s sex, race, and age. It is important to note that certain blood-related conditions, such as sickle-cell anemia, affect particular demographic groups at higher rates.
Learn more about sickle cell anemia in African Americans here.
A doctor may request frequent hematocrit tests to monitor the effect of chemotherapy on a person’s bone marrow.
Both high and low hematocrit levels can be detrimental to a person’s health and result from various conditions and lifestyle factors.
What are normal hematocrit levels?
Different institutions will define normal hematocrit levels differently. However, a 2017 cross-population study found the following ranges to be typical.
- Male: 42-52%
- Female: 37-47%
- Children: 30–44%, depending on their age and sex
Newborn babies have high hematocrit levels that gradually decrease as they get older.
If a person has recently received a blood transfusion, it may affect their results. Additionally, pregnant individuals may have lower levels than usual because the body increases its blood volume during pregnancy.
Other factors, such as smoking and chronic obstructive pulmonary disease (COPD), may push levels into a higher range.
Low levels
A hematocrit level below 35% in women and 41% in men is low. A level under this value can signify chronic anemia.
High levels
Hematocrit levels above the typical ranges can have adverse effects. It may indicate serious underlying health conditions.
Accuracy of results
Results from hematocrit tests are typically accurate and provide a clear reading of a person’s red blood cell levels.
However, the percentage of red blood cells in someone’s blood can change depending on various lifestyle factors and even environmental changes. According to research, red blood cell counts tend to increase at high altitudes.
Exercise, particularly strength training, may also affect hematocrit levels. A 2018 study found that females who participated in 16 weeks of strength exercise had lower levels at the end than when they started. However, the study had a small sample size of 26 middle-aged, sedentary Turkish women. This means that these findings aren’t necessarily representative of a wider population.
Dehydration can also raise hematocrit levels, so this test is useful if a doctor suspects severe dehydration is the cause of a person’s symptoms.
When a person has low hematocrit levels, they tend to present with the following symptoms:
- pale complexion
- weakness
- fatigue
- low energy
- trouble breathing
- irregular heartbeat
- cold hands or feet
These symptoms also indicate anemia, a condition where hemoglobin levels are lower than normal. Hemoglobin is a protein found in red blood cells that carries oxygen around the body.
Mild anemia is treatable, and it is particularly common in women. Severe anemia could signal a more serious underlying health condition that requires more extensive treatment.
Doctors associate anemia with several health conditions, including:
Nutrient deficiency
A person may lack B12, folate, or iron in their diet.
Learn more about how nutrient deficiency anemia is diagnosed and treated.
Chronic bleeding
This commonly occurs due to digestive tract ulcers, which are sores caused by the bacteria H.
pylori or chronic use of anti-inflammatory medications such as ibuprofen, other nonsteroidal anti-inflammatory drugs (NSAIDs), and aspirin. Many women also experience excessive blood loss from heavy menstrual bleeding.
Bone marrow disorder
This includes aplastic anemia, which damages stem cells in bone marrow.
Cancer
These cancers spread to bone marrow, such as leukemia and lymphoma.
Learn more about bone marrow cancers here.
Kidney failure
Kidney disease can lower the production of red blood cells, reducing hematocrit levels.
Thalassemia
When a person has this condition, their body does not produce enough hemoglobin.
Learn more about thalassemia here.
Sickle cell anemia
This condition changes the shape of red blood cells. These cells die earlier than normal, and they also clump together, which impairs blood flow.
Learn more about sickle cell anemia here.
Autoimmune disease
Conditions like rheumatoid arthritis and lupus may reduce red blood cell count.
Learn more about autoimmune diseases here.
When a person has high hematocrit levels, they tend to present with these symptoms:
- flushed skin
- dizziness
- vision problems
- headaches
- enlarged spleen
These symptoms signal polycythemia, a condition where the body produces too many red blood cells. This means blood is thicker and clots more easily.
Doctors cannot cure polycythemia, so treatment focuses on symptom management. The main goal is to avoid stroke and deep vein thrombosis (DVT), which is a blood clot usually occurring in a deep vein in the leg.
In some cases, dehydration causes polycythemia. When a person does not drink enough, their plasma levels drop, increasing the proportion of red blood cells in their blood volume. A person can lower their red blood cell count by rehydrating.
Some conditions that can cause high hematocrit levels include:
Lung or pulmonary disease
When the lungs cannot absorb oxygen effectively, and oxygen levels drop, the body compensates by making more red blood cells.
One common pulmonary disease causing this is COPD.
Learn more about COPD here.
Heart disease
If the structure of a person’s heart reduces its ability to pump blood around the body, it can no longer sustain vital organs with oxygen. To try and overcome the oxygen deficit, the body produces more red blood cells.
Learn more about heart disease here.
Kidney cancer
Sometimes kidney cancer cells create more erythropoietin. Erythropoietin is a hormone that tells the bone marrow to create more red blood cells.
Learn more about kidney cancer here.
Genetic disease
The JAK2 gene, which controls the number of blood cells made in the bone marrow, can affect certain conditions. When someone has a mutated JAK2 gene, the body could make a protein that signals the bone marrow to create more red blood cells than it needs.
Learn more about genetic disorders here.
A person should speak with a doctor if they are experiencing any of the symptoms listed above that could be a sign of high or low hematocrit levels, including fatigue, weakness, vision problems, and dizziness.
These symptoms can also indicate an underlying condition, so a person must contact a doctor promptly to prevent future complications.
If a person is receiving chemotherapy treatment, a doctor should perform regular hematocrit tests to monitor bone marrow health.
Hematocrit is the percentage of blood cells in a person’s blood volume. A doctor may test an individual’s hematocrit level due to certain symptoms.
A low hematocrit level means there are too few red blood cells in the body. In these cases, a person may experience symptoms that signal anemia. Common symptoms include fatigue, weakness, and low energy.
If a person has too many red blood cells, they have a high hematocrit level. A person may experience dizziness and headaches, which can be a sign of the condition polycythemia.
Demographic and lifestyle factors can influence a person’s hematocrit levels. For example, males tend to have higher levels than females. Pregnant individuals can experience a decrease in hematocrit levels, and strength training may also reduce levels.
There are also several health conditions that can cause hematocrit levels outside the normal range. Excessive bleeding, thalassemia, and kidney disease are causes of low levels. COPD and sickle cell anemia can cause high levels.
Read this article in Spanish.
norm in a child, women, men, causes of increased, decreased values in the blood
Hematocrit is one of the blood indicators that registers the total volume of all formed elements, and these are erythrocytes, leukocytes and platelets, in relation to the total volume. Moreover, 99% of the volume of all these elements falls on erythrocytes. The hematocrit (Ht) is expressed as a percentage, but a liter per liter (L/L) can also be selected.
Human blood contains from 36 to 48% of formed elements, it also contains plasma, water, proteins, carbohydrates and salts.
Hematocrit is determined simply: a certain amount of blood is poured into a special tube with graduation, then it is sent to a centrifuge, and at the end of the process, the fraction of the length of the tube that was filled with erythrocyte mass is determined.+measures+how+much+space+in+the+blood+is+occupied+by+red+blood+cells..jpg)
Also, laboratories now use automatic hematology analyzers that allow you to get data in just a few minutes.
Blood hematocrit norm
The body of an adult healthy person contains about 5 liters of blood. Erythrocytes, leukocytes and platelets cannot be called cells, they do not have the necessary parameters for this. Therefore, they are called formed elements. Different people have different amounts of these elements per liter of blood. For example, according to statistics, the hematocrit in men is higher and equal to 40-41%, sometimes this figure can reach 51%.
Hematocrit in women is slightly lower and usually ranges from 36-42%. The reason for this is such a physiological feature as menstruation. As for the period of pregnancy, here this figure begins to decrease in the second half, and this is also not a pathology.
Hematocrit in children always depends on age, therefore, before drawing conclusions from the analysis, it is necessary to find out how many months or years the baby is.
In newborn babies, this figure can be equal to 44-62%, at the age of 3 months it decreases and the figure becomes up to 44%, from 3 months to 1 year the figures can range from 32 to 43%. In the first ten years, Ht in boys can rise to 52%, and in girls it can be at around 35-47%. In subsequent years, the hematocrit norm is equal to the same indicator that is recorded in adults.
Causes of increased hematocrit
Why can it happen that the hematocrit in the blood test is elevated? There are pathological and physiological causes, so before starting any treatment, it is important to understand their origin.
Pathological causes include the following diseases and conditions:
- Dehydration (dehydration). Due to the fact that the amount of blood that circulates through the vessels decreases, the formed elements are in a more concentrated state. This happens with vomiting, diarrhea, heavy sweating, overheating, lack of fluid.
- Second and third degree burns.
In this case, blisters appear on the body, which are filled with plasma, and it appeared in them from the bloodstream. Therefore, the blood becomes thicker, and the concentration of formed elements increases. - Peritonitis, thrombosis or diabetes mellitus.
- Chronic hypoxia.
- Regular use of glucocorticosteroids or diuretics.
- Kidney disease – hydronephrosis.
- Almost all blood diseases, including leukemia.
- Polycystic.
- Heart defects, ischemic heart disease.
- Erythremia.
- Many lung diseases, including asthma, bronchitis.
- Severe bleeding.
In this case, blisters appear on the body, which are filled with plasma, and it appeared in them from the bloodstream. Therefore, the blood becomes thicker, and the concentration of formed elements increases.However, hematocrit analysis alone is not enough to make an accurate diagnosis, it is not very informative. Therefore, it is often done as part of a general blood test, and further therapy tactics are already built on it, if it turns out to be necessary.
But elevated hematocrit can also be the result of certain physiological phenomena.
In this case, deviations of this indicator cannot be considered pathological. High Ht in comparison with the norm is detected in people who smoke constantly and for a long time, which is associated with the development of chronic oxygen starvation of tissues and increased production of red blood cells.
Residents of high mountain regions and mountaineers who spend a lot of time at altitude also have Ht in the range of 51-52%. This is all connected with the same oxygen starvation and the need for the body to compensate for this lack. Also, elevated Ht is typical for athletes who take anabolics that help them gain the required amount of muscle mass.
Manifestations and symptoms of elevated hematocrit
If the hematocrit in the blood is elevated, then this will not necessarily be expressed by certain symptoms. However, it should be remembered that this condition is always expressed by an increase in blood viscosity, which creates a great threat for the formation of blood clots and clogging of both small and large vessels.
If this happens in the coronary arteries, then myocardial infarction develops against the background of thrombosis. If a thrombus forms in the pulmonary artery, then death occurs in 70% of all cases. If the arteries of the brain are affected, then this leads to the development of an ischemic stroke. With thrombosis of the vessels of the legs, gangrene begins to develop.
Therefore, it is important to find out the cause of elevated Ht as soon as possible and start timely treatment.
Reasons for low hematocrit
A decrease in hematocrit can occur without any pronounced symptoms, so this result is usually detected after a blood test and is an unexpected discovery for a person.
The main reasons why the hematocrit may be low are:
- virtually all anemias, including iron deficiency, folate deficiency, B12 deficiency;
- violation of the production of red blood cells due to pathologies of the bone marrow, including oncological ones;
- cirrhosis of the liver;
- diseases of the urinary system;
- hemolysis or destruction of red blood cells;
- chronic bleeding;
- increase in circulating blood volume;
- hyperproteinemia;
- lead intoxication;
- acute infections;
- the use of anticoagulants and similar drugs that affect the composition of the blood.
Decreased hematocrit may have physiological causes. This is work associated with a long stay in one position, starvation or adherence to strict diets, a large amount of fluid that enters the body, alcoholism, the use of large amounts of salt, the period of menstruation.
Manifestations and symptoms of low hematocrit
The reasons for the drop in hematocrit will directly affect what symptoms a person experiences. For example, if it is anemia, then there will be such complaints:
- headache and constant weakness;
- impaired consciousness and breathing;
- dizziness, nausea or vomiting;
- constant thirst;
- lack of strength and exercise intolerance.
If the cause is kidney and urinary system diseases, then there will be complaints about a decrease in the amount of urine excreted, pain in the lumbar region, urination disorder, and changes in blood pressure.
With cirrhosis of the liver, complaints will be of pain in the right side of the abdomen under the ribs, the appearance of spider veins on the skin, indigestion, excessive formation of gases, a feeling of fullness in the abdomen, in advanced cases – internal bleeding.
What tests are needed?
To find out the relative content of all formed elements in the blood, it is necessary to analyze the hematocrit. It is done as part of a general blood test (CBC), when, together with Ht, the number of all elements is calculated, and the ESR is also determined.
Usually, it is with the KLA that a patient’s examination begins to identify a particular disease, or it is carried out for preventive purposes as part of a medical examination, medical examination.
Both venous blood and capillary fingerstick blood can be used for analysis. It is best to take the test in the morning, before breakfast. This allows you to get the right readings that will help the doctor determine if Ht is elevated or low, or its values are within the normal range.
What do the results of a clinical blood test say? (continued3)
- Home
- Interesting
- Articles
- Laboratory
- What Clinical Indicators Tell. ..
..9 0095
WE continue to acquaint our readers with the diagnostic value of clinical blood tests – and in the previous article we have already discussed such of them as erythrocytes and hemoglobin.
What other indicators are used along with those indicated to monitor the state of both the blood itself and the body as a whole? Traditionally, we address our question to the head of the clinical diagnostic laboratory of the Floris Medical Center LARISA ROGULSKAYA.
– One such indicator is hematocrit. This indicator reflects the volume fraction (%), which is erythrocytes from the total blood volume. Like any other laboratory value, hematocrit must be evaluated in conjunction with other indicators. An incorrect assessment threatens with an erroneous opinion about the patient’s state of health. For example, in a patient in shock, the hematocrit may be normal due to blood clots, but the red blood cell count may be reduced due to blood loss. Therefore, immediately after bleeding or blood transfusion, the hematocrit value is not indicative of the degree of anemia.
But such difficulties with interpretation do not at all detract from the value of the hematocrit value in the clinic. Normally, this figure in adult women is 35-47%, in adult men – 39-50%. An increase in the hematocrit value is noted in some malignant blood diseases, it can be observed in congenital heart defects, respiratory failure, some tumors and polycystic kidney disease. Abnormally elevated hematocrit often occurs with burn disease, peritonitis, dehydration of the body as a result of severe diarrhea or vomiting, sometimes with diabetes.
Decreased hematocrit, a common sign of anemia, may occur with uncontrolled intravenous drip infusions.
One of the most important indicators of a clinical blood test related to erythrocytes is the ESR (erythrocyte sedimentation rate). This is an indicator of the rate of separation of blood mixed with a reagent that prevents its coagulation in a thin glass capillary into two layers: a transparent top (blood plasma) and a red-colored bottom (erythrocytes and other blood cells).
In fact, how many millimeters the erythrocytes settle within an hour, this will be the ESR indicator.
In healthy adult males, the ESR is 1-10 mm/hour, in some up to 15, and in men over 50 it can be up to 20 mm/hour. Healthy adult women have 215 mm/hour, some have up to 20, and women over 50 may have up to 30 mm/hour. Determination of ESR is a mandatory component of a clinical blood test, performed to detect inflammation of a different nature, and also makes it possible to suspect a tumor process with a high degree of probability, in which the indicator is characterized by consistently high numbers. ESR values also increase in case of poisoning, acute and chronic infections, including pneumonia, osteomyelitis, tuberculosis, myocardial infarction, joint diseases of various origins, injuries and fractures, conditions after operations, anemia, kidney diseases, as well as when taking certain medications. . A decrease in ESR values (approaching zero) may indicate a dangerous malignant blood disease.