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Hemoglobin Variants Blood Tests

Last updated Sept. 3, 2018

Approved by: Krish Tangella MD, MBA, FCAP

Microscopic pathology image showing Red Blood Cells on a peripheral smear

What are the other Names for this Test? (Equivalent Terms)

  • HB Variants Blood Tests
  • Hemoglobin Abnormalities Blood Test
  • Hereditary Persistence of Fetal Hemoglobin Blood Test (see HB Variants Blood Tests)

What is Hemoglobin Variants Blood Tests? (Background Information)

  • Hemoglobin is an oxygen-carrying protein that makes up the bulk of red blood cells. Different variants of hemoglobin arise from mutations of the genetic blueprints that give instructions for hemoglobin
  • Oxygen is extremely important in sustaining human life. It is so important that one-third of the body’s 75 trillion cells are red blood cells, which are vehicles for oxygen transport
  • The “bed” of these vehicles, the storage part, is hemoglobin. Each red blood cell is 97% hemoglobin, implying that there is a large amount of hemoglobin needed at any one time – i.e., around 0.75 kg 
  • Hemoglobin is actually an assembly of four individual protein parts, called chains. Two of them are identical to each other. In other words, hemoglobin is formed by two pairs of protein chains. There are several different types of hemoglobin in the body:
    • Hemoglobin A: The most abundant form of hemoglobin, it makes up 95-98% of the hemoglobin in the body. Hemoglobin A consists of 2 alpha chains and 2 beta chains
    • Hemoglobin A2: It is a rare hemoglobin type and makes up 2-3% of the hemoglobin in the body. Hemoglobin A2 consists of 2 alpha and 2 delta chains
    • Hemoglobin F: Also called fetal hemoglobin, it is produced by the fetus during pregnancy and helps transport oxygen to the growing fetus. It makes up only 1-2% of the hemoglobin outside of pregnancy. Hemoglobin F is composed of 2 alpha and 2 gamma chains
  • The blueprints that give instructions for the production of different types of hemoglobin chains are called genes. Four different genes give instructions for alpha chains, and two each give instructions for beta, gamma, and delta chains
  • Alterations or mutations in any of these genes may have harmful effects on hemoglobin function. This is because the resulting protein may take on a suboptimal structure. For example, a tiny mutation in the beta chain of hemoglobin, resulting in a change of one amino acid in the 146 total that make up the protein, is responsible for causing sickle-cell anemia. (This altered protein is called hemoglobin S; S for “sickle”)
  • There are hundreds of known variants of hemoglobin. However, only a handful of these are common enough and cause severe-enough symptoms to have any clinical significance. Other than hemoglobin S, these include hemoglobin C and hemoglobin E
  • Given the fact that hemoglobin makes up for such a large part of the red blood cells (RBCs), alterations in hemoglobin structure may result in RBCs that are misshapen or otherwise unstable. These are readily degraded by the body potentially causing anemia, owing to a shortage of the RBCs
  • Each individual possess two copies of hemoglobin in all of their genes. One of these is inherited from the father and the other from the mother. Thus, having one altered copy of hemoglobin is compensated for by the other healthy copy. Such individuals (with one altered copy of hemoglobin) are called carriers because they do not exhibit any symptoms themselves, but may have children who do. Having two altered copies of hemoglobin is necessary to exhibit symptoms of altered hemoglobin function

The Hemoglobin Variants Blood Tests are a group of tests to help identify the presence of non-standard forms of hemoglobin. These tests include:

  • Complete blood count (CBC): An analysis of the number, composition, and size of all blood cells in circulation at one time
  • Blood smear: Microscopic observation of the size, shape, color, and other visual characteristics of a sample of blood cells
  • Hemoglobinopathy evaluation: An analysis of the relative amounts of the different types of hemoglobin present in red blood cells
  • DNA analysis: Genetic testing, including family studies, to determine if an individual’s genetic blueprint contains mutations in alpha and beta chain genes

What are the Clinical Indications for performing the Hemoglobin Variants Blood Test?

Following are the clinical indications for performing the Hemoglobin Variants Blood Tests:

  • Screening of a fetus during pregnancy (prenatal screening)
  • Routine screening; the test is especially performed in sub-Saharan African populations
  • Family history of sickle cells
  • Family history of hemoglobin mutations
  • Shortness of breath
  • Diffuse pain or pain in the upper abdomen
  • Vision loss
  • Stroke
  • Unexplained tissue destruction
  • Paleness
  • Fatigue
  • Jaundice
  • Developmental problems

How is the Specimen Collected for Hemoglobin Variants Blood Test?

Following is the specimen collection process for Hemoglobin Variants Blood Tests:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected, by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Hemoglobin Variants Blood Test Result?

The presence of significant amounts of altered forms of hemoglobin may indicate:

  • Sickle cell anemia
  • Thalassemia(s)
  • Various other hemoglobinopathies (disorders with abnormal hemoglobin types) 

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The red blood cells with hemoglobin S variant may be induced to sickle during times of stress. This includes oxygen deprivation and exposure to chemicals such as metabisulfite

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: May 15, 2015
Last updated: Sept. 3, 2018