How are they tested?Laboratory Tests
Laboratory testing for hemoglobin variants is an exploration of the “normalness” of the red blood cells (RBCs), an evaluation of the hemoglobin inside the RBCs, and an analysis of relevant gene mutations or deletions. Each test provides a piece of the puzzle, giving the clinician important information about which variants may be present. The tests that are ordered to search for hemoglobin variants are also used for thalassemia workups. Searching for both is important because thalassemia is sometimes inherited along with a hemoglobin variant.
CBC (complete blood count). The CBC is a snapshot of the cells circulating in your bloodstream. Among other things, the CBC will tell the doctor how many red blood cells are present, how much hemoglobin is in them, and give the doctor an evaluation of the size and shape of the red blood cells present. Mean corpuscular volume (MCV) is a measurement of the size of the red blood cells. A low MCV is often the first indication of thalassemia. If the MCV is low and iron-deficiency has been ruled out, the person may be a thalassemia trait carrier or have one of the hemoglobin variants that cause microcytosis (for example, Hb E).
Blood smear (also called a peripheral smear and a manual differential when white cells are examined). In this test, a trained laboratorian looks at a thin layer of blood, treated with a special stain, on a slide, under a microscope. The number and type of white blood cells, red blood cells, and platelets can be assessed and evaluated to see if they are normal and mature. A variety of disorders affect normal blood cell production. The red blood cells may be:
MicrocyticHypochromicVarying in size (anisocytosis) and shape (poikilocytosis)Having a nucleus (not normal in a mature RBC)Having uneven hemoglobin distribution (producing “target cells” that look like a bull’s-eye under the microscope).
The greater the percentage of abnormal-looking red blood cells, the greater the likelihood of an underlying disorder and of impaired oxygen-carrying capability.
Hemoglobin variant testing. These tests identify the type, and measure the relative amount, of hemoglobins present in the red blood cells. Most of the common variants can be identified using one of these tests or a combination. The relative amounts of any variant hemoglobin detected can help diagnose combinations of hemoglobin variants and thalassemia (compound heterozygotes).
DNA analysis. This test is used to investigate deletions and mutations in the alpha and beta globin-producing genes. Family studies can be done to evaluate carrier status and the types of mutations present in other family members. DNA testing is not routinely done but can be used to help diagnose hemoglobin variants, thalassemia, and to determine carrier status.
Is any test preparation needed?
No test preparation is needed.
Why are they done?
Testing for hemoglobin variants is done to:
Screen for common hemoglobin variants in newborns. In all states, this has become a standard part of newborn screening. Infants with variants such as Hb S can benefit from early detection and treatment.
Prenatal screening is also done in some areas on high-risk mothers: those with an ethnic background associated with a higher prevalence of hemoglobin variants (such as those of African descent) and those with affected family members. Screening may also be done in conjunction with genetic counseling prior to pregnancy to determine possible carrier status of parents.
Identify variants in asymptomatic parents with an affected child.Identify hemoglobin variants in those with symptoms of unexplained anemia, microcytosis, and/or hypochromasia. It may also be ordered as part of an anemia investigation.
