What is a hemoglobin blood test. How is it performed. Why is it important for diagnosing anemia and other health conditions. When should you get tested. Can you take a hemoglobin test at home.

Understanding Hemoglobin and Its Role in the Body

Hemoglobin is a crucial component of our blood that plays a vital role in our overall health. This iron-rich protein is found in red blood cells (RBCs) and is responsible for giving them their distinctive red color. But what exactly does hemoglobin do?

The primary function of hemoglobin is to transport oxygen from the lungs to various tissues and organs throughout the body. It acts as a carrier, picking up oxygen molecules in the lungs and delivering them to cells that need this essential element for energy production and other vital processes. Additionally, hemoglobin helps transport carbon dioxide from the tissues back to the lungs, where it can be exhaled.

Given its critical role, measuring hemoglobin levels can provide valuable insights into a person’s health status. But how exactly is hemoglobin measured?

How is Hemoglobin Measured?

Hemoglobin is typically measured as part of a Complete Blood Count (CBC) test. The measurement is expressed in grams per deciliter (g/dL) of blood or grams per liter (g/L) of blood. This quantification helps healthcare providers assess whether an individual has normal, low, or high hemoglobin levels.

The Purpose and Importance of Hemoglobin Testing

Why do healthcare providers order hemoglobin tests? There are several reasons:

• To detect anemia: Low hemoglobin levels often indicate anemia, a condition characterized by a deficiency of red blood cells.
• To diagnose other health problems: Abnormal hemoglobin levels can be indicative of liver or kidney disease, blood disorders, malnutrition, certain types of cancer, and heart or lung conditions.
• To monitor treatment effectiveness: For patients being treated for anemia or other conditions affecting hemoglobin levels, regular testing can help track progress and adjust treatment as needed.
• To assess overall health: As part of a routine CBC, hemoglobin testing contributes to a comprehensive picture of an individual’s health status.

Is hemoglobin the only component measured in a CBC? No, a CBC also typically includes measurements of:

• White blood cells (WBCs), which are crucial for immune function
• Platelets, which enable blood clotting
• Hematocrit, the proportion of blood volume made up of RBCs

When Should You Get a Hemoglobin Test?

Knowing when to get a hemoglobin test is crucial for maintaining optimal health. Healthcare providers may recommend this test under various circumstances:

Symptoms of Low Hemoglobin or Anemia

If you’re experiencing any of the following symptoms, your doctor might order a hemoglobin test:

• Persistent fatigue or weakness
• Shortness of breath, especially during physical activity
• Dizziness or lightheadedness
• Pale or yellowish skin
• Frequent headaches
• Irregular heartbeat

Signs of High Hemoglobin Levels

Although less common, high hemoglobin levels can also be problematic. Symptoms that might prompt testing include:

• Disturbed vision
• Dizziness
• Severe headaches
• Slurred speech
• Flushing or reddening of the face

Existing Health Conditions

Certain health conditions may necessitate regular hemoglobin testing. These include:

• Blood disorders such as sickle cell disease or thalassemia
• Diseases affecting the lungs, liver, kidneys, or cardiovascular system
• Recent significant bleeding from trauma or surgery
• Nutritional deficiencies, particularly iron deficiency
• Chronic infections
• Cognitive impairment, especially in older adults
• Certain types of cancer

Does a hemoglobin test always indicate a suspected health problem? Not necessarily. Often, hemoglobin is measured as part of routine health checks, even in the absence of specific symptoms or concerns.

The Hemoglobin Testing Process: What to Expect

Understanding the hemoglobin testing process can help alleviate any concerns you might have about the procedure. Here’s what you can expect:

Where is the Test Performed?

Hemoglobin tests are typically conducted in healthcare settings such as:

• Doctor’s offices
• Clinics
• Laboratories
• Hospitals

The test is performed by licensed healthcare professionals who are trained in blood collection procedures.

Blood Collection Methods

There are two primary methods for collecting blood for a hemoglobin test:

1. Blood draw: This involves collecting a small amount of blood from a vein, usually in the arm. The healthcare provider will clean the area, insert a small needle, and draw the required amount of blood into a vial.
2. Fingerstick test: In this method, the healthcare provider pricks your fingertip with a small, sharp lancet to collect a few drops of blood.

The method used often depends on the specific requirements of the test and the preference of the healthcare provider.

At-Home Hemoglobin Testing: Possibilities and Limitations

With the rise of home health testing, you might wonder if it’s possible to measure your hemoglobin levels at home. The answer is yes, but with some caveats.

How Do At-Home Hemoglobin Tests Work?

At-home hemoglobin tests typically involve a fingerstick method. You prick your finger with a provided lancet and place a drop of blood on a test strip or into a small device. The test then provides an estimate of your hemoglobin levels.

Accuracy Concerns

While at-home tests can provide a general indication of hemoglobin levels, they may not be as accurate as laboratory tests. Factors that can affect accuracy include:

• User error in sample collection or test administration
• Environmental factors such as temperature or humidity
• Individual variations in blood composition
• The quality and calibration of the testing device

Are at-home hemoglobin tests suitable for everyone? Not necessarily. Some individuals, such as those with certain medical conditions, may require more precise measurements that can only be obtained through laboratory testing.

When to Use At-Home Tests

At-home hemoglobin tests can be useful for:

• Regular monitoring for individuals with known anemia or other conditions affecting hemoglobin levels
• Initial screening before consulting a healthcare provider
• Monitoring response to dietary changes or supplements aimed at improving iron levels

However, it’s crucial to remember that at-home tests should not replace professional medical advice or laboratory testing when diagnosing or managing health conditions.

Interpreting Hemoglobin Test Results

Understanding your hemoglobin test results is crucial for assessing your health status. However, interpretation should always be done in consultation with a healthcare provider who can consider your individual health context.

Normal Hemoglobin Ranges

Normal hemoglobin levels can vary based on factors such as age, sex, and overall health. Generally, normal ranges are:

• For men: 13.5 to 17.5 grams per deciliter (g/dL)
• For women: 12.0 to 15.5 g/dL
• For children: Ranges vary by age

Low Hemoglobin Levels

Low hemoglobin levels (below the normal range) often indicate anemia. Causes of low hemoglobin can include:

• Iron deficiency
• Vitamin B12 or folate deficiency
• Chronic diseases
• Blood loss
• Certain genetic conditions

High Hemoglobin Levels

High hemoglobin levels (above the normal range) can be indicative of:

• Polycythemia vera, a blood disorder where the body produces too many red blood cells
• Dehydration
• Lung diseases that affect oxygen levels
• Living at high altitudes
• Smoking

How do healthcare providers use hemoglobin test results? They consider these results alongside other factors such as symptoms, medical history, and additional test results to make a comprehensive health assessment.

The Cost of Hemoglobin Testing: What to Consider

The cost of a hemoglobin test can vary widely depending on several factors. Understanding these can help you prepare for potential expenses:

Factors Affecting Cost

• Insurance coverage: If you have health insurance, check whether the test is covered and what your out-of-pocket costs might be.
• Testing location: Costs can differ between hospitals, clinics, and laboratories.
• Type of test: A standalone hemoglobin test might cost differently than a full CBC panel.
• Geographic location: Healthcare costs can vary significantly by region.

Estimating Costs

Without insurance, a CBC test (which includes hemoglobin measurement) can range from $140 to $622. However, prices can be lower or higher depending on the specific circumstances and location.

For those with insurance, out-of-pocket costs typically range from $0 to $100, depending on your plan’s coverage and whether you’ve met your deductible.

Cost-Saving Tips

If you’re concerned about the cost of hemoglobin testing, consider these options:

• Check with multiple providers or laboratories for price comparisons.
• Ask about cash pay discounts if you’re uninsured.
• Look into community health centers or sliding scale clinics that offer reduced-cost testing.
• Discuss with your healthcare provider if the test is absolutely necessary or if there are alternative options.

How can you find out the exact cost of your hemoglobin test? The best approach is to contact your insurance provider and the testing facility directly. They can provide the most accurate cost estimate based on your specific situation.

Preparing for Your Hemoglobin Test: Tips and Considerations

Proper preparation can help ensure accurate results from your hemoglobin test. While it’s generally a straightforward procedure, there are a few things to keep in mind:

Before the Test

• Fasting: In most cases, you don’t need to fast before a hemoglobin test. However, if your doctor has ordered additional blood tests along with the hemoglobin test, fasting might be required. Always follow your healthcare provider’s specific instructions.
• Medications: Inform your doctor about any medications you’re taking, including over-the-counter drugs and supplements. Some medications can affect hemoglobin levels.
• Hydration: Unless instructed otherwise, stay well-hydrated before the test. Dehydration can affect blood concentration and potentially skew results.
• Time of day: Hemoglobin levels can fluctuate slightly throughout the day. If you’re monitoring levels over time, try to schedule your tests at consistent times.

During the Test

The actual blood draw or fingerstick procedure is usually quick and involves minimal discomfort. Here’s what to expect:

• For a blood draw: The healthcare provider will clean the area (usually the inside of your elbow), insert a small needle into a vein, and collect the blood sample in a vial.
• For a fingerstick test: Your finger will be pricked with a small lancet, and a few drops of blood will be collected.

The entire process typically takes only a few minutes.

After the Test

After your blood is collected:

• Apply pressure to the puncture site to stop any bleeding.
• Keep the bandage on for the recommended time (usually a few hours).
• Avoid strenuous activities with the affected arm for a few hours if you had a blood draw.
• Stay hydrated.
• If you experience any unusual symptoms like prolonged bleeding or severe bruising, contact your healthcare provider.

How long does it take to get hemoglobin test results? In many cases, results are available within a few hours to a day. However, the exact timing can vary depending on the laboratory and whether other tests are being performed on the same blood sample.

Remember, preparing adequately for your hemoglobin test can help ensure accurate results and a smooth testing experience. Always follow the specific instructions provided by your healthcare provider, as they may have additional recommendations based on your individual health situation.

Hemoglobin Blood Test – Testing.com

Test Quick Guide

Hemoglobin is an iron-rich protein found in Red Blood Cells (RBC), giving them their unique red color. It is primarily responsible for carrying oxygen from your lungs to the tissues and organs of your body.

A hemoglobin test is often used to detect anemia, which is a deficiency of RBC that can have adverse health effects. While hemoglobin can be tested on its own, it’s more often tested as part of a complete blood count (CBC) test that also measures levels of other types of blood cells.

About the Test

Purpose of the test

A hemoglobin test is used to find out how much hemoglobin is in your blood. It is most often used to determine if you have low levels of RBC, a condition known as anemia.

In addition to identifying anemia, a hemoglobin test can be involved in the diagnosis of other health problems like liver and kidney disease, blood disorders, malnutrition, some kinds of cancer, and heart and lung conditions.

If you have been treated for anemia or other conditions that can affect hemoglobin levels, a hemoglobin test may be ordered to check your response to treatment and monitor the progression of your overall health.

What does the test measure?

A hemoglobin test measures the volume of the protein hemoglobin found in your RBC. It is measured in grams per deciliter (g/dL) of blood or grams per liter (g/L) of blood.

Hemoglobin is one component of RBC and gives these cells their distinct red color. A main function of hemoglobin is to carry oxygen to cells throughout the body. It also has a role in transporting carbon dioxide from the organs and tissues back to the lungs where it can be exhaled.

When measured as part of a CBC test, other blood components may be measured including:

• White blood cells (WBCs), which are involved in immune function
• Platelets that enable the blood to clot when needed
• Hematocrit, the proportion of blood made up of RBC

When should I get this test?

Hemoglobin is one indicator of how much oxygen your body may be getting. Levels can also reflect whether you have enough iron in your blood. Accordingly, your provider may order a CBC to measure hemoglobin if you are experiencing signs and symptoms of low oxygen or iron. These symptoms can include:

• Fatigue
• Shortness of breath during physical activity
• Dizziness
• Skin that is paler or yellower than usual
• Headaches
• Irregular heartbeat

Although less common, high hemoglobin levels can also cause health problems. A hemoglobin test may be ordered if you have signs of abnormally high hemoglobin levels, such as:

• Disturbed vision
• Dizziness
• Headache
• Slurred speech
• Reddening of the face

Your provider may also order a hemoglobin test if you have been diagnosed with or are suspected of having:

• Blood disorders like sickle cell disease or thalassemia
• Diseases affecting the lungs, liver, kidneys, or cardiovascular system
• Significant bleeding from trauma or surgery
• Poor nutrition or a diet that is low in vitamins and minerals, specifically iron
• Significant long-term infection
• Cognitive impairment, especially in the elderly
• Certain types of cancer

You most often see results for a hemoglobin test as part of a CBC test, a common collection of tests often ordered by a provider to assess your overall health. For this reason, having a hemoglobin test does not necessarily mean your provider suspects a health problem.

Finding a Hemoglobin Test

How can I get a Hemoglobin test?

A hemoglobin test is most commonly conducted by a licensed professional in a health care setting. It is usually part of a CBC test done in a doctor’s office, clinic, laboratory, or hospital. The test may be performed with a blood draw or a fingerstick test.

A hemoglobin test is normally prescribed by a doctor, so talk with your health care provider if you have symptoms that could be related to abnormal hemoglobin levels.

Can I take the test at home?

There are options for at-home hemoglobin testing. At-home tests use one or more drops of blood to provide an estimation of hemoglobin levels. The drops of blood are obtained by pricking your finger with a tiny needle.

At-home hemoglobin tests may produce values that are less accurate than laboratory testing, especially for certain patients. For the most accurate results, hemoglobin tests should be administered by trained laboratory personnel.

Your doctor can help you understand if at-home testing is appropriate in your case, and never use at-home tests in place of consultation with your doctor about your health.

How much does the test cost?

Hemoglobin tests are usually part of a CBC. The cost for a CBC panel depends on whether you have health insurance and whether it covers the test. Other factors that can affect the cost include where your blood is drawn and the charges for the laboratory where your provider sends your blood sample.

Check directly with your doctor or your insurance provider to find out about expected costs, including any copays or deductibles.

Taking a Hemoglobin Test

Hemoglobin is measured by taking a blood sample. A hemoglobin test is most often part of a blood draw ordered and conducted by a medical professional in a health care setting.

In infants, hemoglobin tests may be conducted by pricking the heel or finger of the child.

Before the test

Unless specified by your provider, no special preparation is needed for a hemoglobin test. In some instances, hemoglobin is tested along with other blood tests. When you are getting more than one blood test, your provider may ask you to not eat anything for a certain amount of time prior to your test. If you have questions or concerns about any test preparation, contact your health care provider for detailed instructions.

During the test

Most hemoglobin tests involve a blood draw from a vein inside your elbow or at the top of your hand. The steps for taking a blood draw include:

1. The area is cleansed with an antiseptic wipe.
2. A band, called a tourniquet, is placed around your arm to increase the pressure in your arm and make your vein more visible and easier to access with a needle.
3. A needle is placed in your vein. A test tube is attached to the needle and is filled with blood. You may feel a pinch or a little pain, which may result in mild bruising or some bleeding.
4. If you are getting other blood tests in addition to a hemoglobin test you may have more than one tube of blood drawn.

For young children, testing may involve a blood sample taken from the heel or finger. Those tests follow these steps:

1. The finger or heel is cleaned with alcohol or an antiseptic wipe.
2. The finger or heel is stuck with a small needle, resulting in 2-3 drops of blood.
3. The first drops of blood are wiped away.
4. As the next drop of blood is produced, a test strip is prepared for analysis.
5. The blood is applied to the test strip so that it can be analyzed on-site.

After the test

Once blood is drawn, the health care provider may apply pressure to the puncture site with a cotton swab. If you are prone to bleeding, they may place an adhesive bandage over the cotton swab to maintain the pressure.

After any blood draw test, such as hemoglobin, it’s important to watch out for dizziness or lightheadedness. Your provider may want you to stay seated for a few minutes until they can determine that you are safe to get up and walk and/or drive.

Other than possible lightheadedness, side effects from a blood draw may include slight bruising at the puncture site.

Hemoglobin Test Results

Receiving test results

Results from a hemoglobin test are often available within a few days after you have had your blood drawn. You may receive results by mail or electronically. Your doctor’s office may also contact you to discuss your test results.

Interpreting test results

The numbers associated with your result are in grams per deciliter or g/dL. Hemoglobin reference ranges may vary depending on age and sex.

The high and low values of a normal test result, called the reference range, may differ depending on the laboratory and the methods used to conduct the test. For this reason, it is essential to look at the reference range listed on your test report.

An example of potential reference range, provided by the American Board of Internal Medicine, is listed in the following tables:

Hemoglobin Reference Range for Adults

Hemoglobin Reference Range Newborns and Infants

While these provide an example of a potential reference range, your results are only considered abnormal based on the range used by the specific laboratory that performed the test.

Because hemoglobin is affected by many factors, it is important that you discuss your results with your provider if you have any concerns. Only your doctor can clarify if your hemoglobin test results are normal for your situation.

If hemoglobin levels are low, it can be a sign of anemia. There are many potential causes of anemia including blood loss, nutritional deficiencies, and many other conditions.

High hemoglobin can also be a sign of underlying health problems including conditions affecting the lung and heart. Dehydration, smoking, living at a high altitude, and some genetic conditions can also lead to high levels of hemoglobin.

Abnormal hemoglobin levels are not a diagnosis of any of these conditions. Instead, your hemoglobin levels are evaluated in the context of your symptoms, other blood counts, and additional test results to diagnose an underlying cause of high or low levels of hemoglobin.

Abnormal hemoglobin test results may or may not require follow-up testing. Hemoglobin is often evaluated alongside other components of a CBC to look for signs of disease or monitor health conditions.

If they feel it is necessary, your doctor may order additional testing if you have low hemoglobin. Often follow-up testing aims to evaluate the cause or causes of anemia. Testing for anemia may include tests such as a reticulocyte count, a renal panel, a liver panel, hemolysis testing, or a blood smear.

Follow-up testing is based on your symptoms, medical history, and the results of other tests. For questions about follow-up testing, make sure to speak with your doctor.

The following questions may be helpful when reviewing your hemoglobin test results with your doctor:

• Was my hemoglobin level abnormal?
• If it was abnormal, do you consider that level to be concerning in my case?
• Are abnormal hemoglobin levels something I can change?
• Do I need to monitor my hemoglobin levels at home?
• Based on my hemoglobin levels, is there any other testing that is needed?

Resources

• CBC Blood Test (Complete Blood Count)
  Learn More
• Red Blood Cell Count (RBC) Test
  Learn More
• Hematrocit Blood Test
  Learn More
• White Blood Cell Count (WBC Blood Test)
  Learn More
• Platelet Count (PLT) Blood Test
  Learn More
• Blood Smear
  Learn More
• Iron Test
  Learn More
• Hemoglobin A1C (HbA1c) Test
  Learn More
• Reticulocyte Count Test
  Learn More
• The Leukemia & Lymphoma Society
  Learn More
• National Library of Medicine: Anemia
  Learn More

Sources

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Hemoglobin and Hematocrit – Clinical Methods

Definition

Hemoglobin (Hb) is the protein contained in red blood cells that is responsible for delivery of oxygen to the tissues. To ensure adequate tissue oxygenation, a sufficient hemoglobin level must be maintained. The amount of hemoglobin in whole blood is expressed in grams per deciliter (g/dl). The normal Hb level for males is 14 to 18 g/dl; that for females is 12 to 16 g/dl. When the hemoglobin level is low, the patient has anemia. An erythrocytosis is the consequence of too many red cells; this results in hemoglobin levels above normal.

The hematocrit measures the volume of red blood cells compared to the total blood volume (red blood cells and plasma). The normal hematocrit for men is 40 to 54%; for women it is 36 to 48%. This value can be determined directly by microhematocrit centrifugation or calculated indirectly. Automated cell counters calculate the hematocrit by multiplying the red cell number (in millions/mm³) by the mean cell volume (MCV, in femtoliters). When so assayed, it is subject to the vagaries inherent in obtaining an accurate measurement of the MCV (see Chapter 152).

Both the hemoglobin and the hematocrit are based on whole blood and are therefore dependent on plasma volume. If a patient is severely dehydrated, the hemoglobin and hematocrit will appear higher than if the patient were normovolemic; if the patient is fluid overloaded, they will be lower than their actual level. To assess true red cell mass, independent radionuclide evaluation of the red cells and plasma (by ⁵¹Cr and ¹³¹I respectively) must be performed.

Technique

Hematocrit

If the hematocrit must be determined quickly, as is often the case when a patient hemorrhages, it may be necessary to measure the hematocrit directly without the use of an automated counter. The materials needed are:

• Lancets

• Alcohol prep pads

• Gauze pads

• Microhematocrit tubes (heparinized)

• Sealant (“Seal-Ease,” “Crit-Seal,” etc)

• Microhematocrit centrifuge

• Microhematocrit reader

• If venipuncture is required: tourniquet, syringe, tube containing anticoagulant (EDTA, citrate)

For hematocrits obtained by fingerstick, wipe the fingertip pad of the fourth finger of the nondominant hand with the alcohol prep pad. Make certain the area is allowed to dry. Prick the fingertip with the lancet. Place the hematocrit tube near the incision site and allow the blood to flow via capillary action into the hematocrit tube until it is two-thirds to three-fourths full or to a predesignated mark on the tube. Avoid “milking” the finger if possible; this causes the expression of tissue fluids and may result in a falsely low hematocrit. Always fill at least three tubes. For hematocrits obtained by venipuncture, draw a sample of blood into the tube containing anticoagulant and mix well. Dip the hematocrit tube into the blood and allow the blood to rise to the desired two-thirds to three-quarters level. Because blood cells naturally sediment, a prior thorough mixing of the blood in the tube is necessary to ensure accurate reading.

After cleaning the outside of the hematocrit tubes of excess blood, invert the tube slowly so that the blood migrates just short of the bottom end of the tube. Seal the bottom of the tube with sealant. Make certain that little or no air is interspersed in the column of blood. If the seal is incomplete, leakage will occur during centrifugation and false readings will be obtained.

Place the tubes in a microhematocrit centrifuge and spin for 3 to 5 minutes at high speed. A shorter spin will not allow for complete sedimentation.

Using either a hematocrit reader or any ruled apparatus, measure the length of the column of the packed red cells and divide it by the length of the whole column of blood (cells and plasma), as in . To obtain the hematocrit, multiply this number by 100%. Average all readings obtained from the different microhematocrit tubes.

Figure 151.1

Microhematocrit tube after sedimentation. The hematocrit is a ratio of the packed cells to total volume.

Example: If the column of packed red cells measures 20 mm and the whole blood column measures 50 mm, the hematocrit is 20/50 = 0.4 or (0.4 × 100%) = 40%.

Hemoglobin

Hemoglobin determinations will usually be performed by an automated cell counter from a tube of well-mixed EDTA-anticoagulated blood filled to a predetermined level. In this assay, all forms of hemoglobins are converted to the colored protein cyanomethemoglobin and measured by a colorimeter. An inadequate sample, whether due to insufficient volume or inadequate anticoagulation, may give false readings. If it is necessary to determine the level of anemia quickly, the hematocrit is an easier, more convenient test.

Hemoglobin Electrophoresis

Hemoglobin electrophoresis measures the mobility of hemoglobin in an electric field; it can therefore detect only those abnormalities in hemoglobin that alter the charge. Electrophoretic mobilities are affected by pH and by the medium in which the test is conducted. Screening tests typically use a hemolysate of anticoagulated blood electrophoresed on cellulose acetate at pH 8.6 to 8.8. If necessary, a further electrophoresis in starch gel at pH 6.2 to 6.8 is performed. At that stage, the work will usually be performed by a specialized laboratory.

Hemoglobin electrophoresis will not readily assess situations where there are neutral amino acid substitutions or where the hemoglobin is normal but the constituent chains are not produced in equal numbers (thalassemias). The diagnosis of alpha thalassemia of a mild to moderate degree cannot be made by hemoglobin electrophoresis; the diagnosis of beta thalassemia may be made by inference from an increase in the Hb A₂.

A standard electrophoresis would look like .

Figure 151.2

A standard hemoglobin electrophoresis (cellulose acetate, pH 8.6).

Basic Science

The molecular weight of hemoglobin is approximately 64,500 daltons. Hb is composed of two pairs of dissimilar chains, α and β, each defined by a specific amino acid sequence and incorporating an iron-containing heme group. Two α–β dimers combine to form a hemoglobin tetramer. This allows for the “heme–heme” interaction necessary for effective oxygen uptake (deoxyhemoglobin → oxyhemoglobin) and delivery (oxyhemoglobin → deoxyhemoglobin). The oxygen affinity of hemoglobin is a function of this heme–heme interaction and of pH (Bohr effect), and is a measure of how many hemoglobin molecules have oxygen bound to them for a given level of oxygen tension. In a normal individual the major hemoglobin is Hb A, constituting approximately 97% of the total hemoglobin. Variations and/or amino acid substitutions in these chains exist. Some are deleterious to the normal function of hemoglobin, whereas others may have relatively normal oxygen affinity and stability. Hemoglobins containing different types of chains make up the remainder of the hemoglobin content in red cells (α₂δ₂ = Hb A₂ approximately 2%; α₂γ₂ = Hb F approximately 1%).

Substitutions in the normal hemoglobin amino acid sequence may result in hemoglobins that have different sub-unit interactions and varying affinities for oxygen. For example, a substitution of the sixth amino acid on the beta chain causes Hb S, or sickle hemoglobin. Hb S has a lower oxygen affinity and surrenders its oxygen more readily. Hb F, a normal minor hemoglobin constituent, has a higher oxygen affinity.

If the oxygen dissociation curve is abnormal, the body will adjust the hemoglobin level to ensure adequate oxygen distribution to the tissues. Thus in a rare disease like hemoglobin Hotel Dieu, the difficulty in extracting oxygen from a variant hemoglobin with increased oxygen affinity could result in a lack of oxygen for the tissues (tissue hypoxia) and a compensatory erythrocytosis. The smaller fraction of oxygen released from the hemoglobin is thereby offset by the increased number of hemoglobin molecules. Similarly, in sickle cell anemia, the decreased oxygen affinity allows these patients more tissue oxygen at any given hemoglobin level.

Clinical Significance

Many anemias are detected by routine laboratory screening performed before the patient is symptomatic. When the patient does have symptoms from an abnormality in the hemoglobin level, the symptoms are often a nonspecific weakness or fatigue. The only finding on physical examination may be pallor; additional changes in the nail beds (such as spooning), glossitis (red tongue), or hepatosplenomegaly (enlarged liver or spleen) may give a clue to the etiology of the anemia. Symptoms are usually related to the level of hemoglobin, its abruptness of onset and its duration. A patient with pernicious anemia may feel well at the same level of hemoglobin that would cause severe weakness in a patient with acute gastrointestinal hemorrhage. This is due to volume compensation by plasma and shifts in the oxygen dissociation curve which occur over time.

When first confronted with an abnormal hemoglobin or hematocrit level, the next step is to assess the red cell indices (see Chapter 152), peripheral smear (Chapter 155), and the reticulocyte count (Chapter 156) in light of the patient’s history and physical examination.

References

1. Adamson JW, Finch CA. Hemoglobin function, oxygen affinity and erythropoietin. Annu Rev Physiol. 1975;37:351. [PubMed: 235878]

2. Bunn HF. Hemoglobin I. Structure and function. In: Beck WS, Hematology. Cambridge, MA: MIT Press, 1981;129.

3. Scott AF. et al. The molecular basis of hemoglobin.