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Laboratory tests

FBC (full blood count). The FBC is a snapshot of the cells and fluid in your bloodstream. Among other things, the FBC will tell the doctor how many red blood cells are present, how much haemoglobin is in them, and measure the size and shape of the red blood cells present. These variables are call red cell indices and include the MCH (mean cell haemoglobin) and MCV (mean cell volume), as measurements of the haemoglobin content and size of the red blood cells. A low MCH or MCV is often the first indication of thalassaemia. If the MCH or MCV is low and iron-deficiency has been ruled out, the person may be a thalassaemia trait carrier. if iron deficiency is present it is difficult to rule out thalassaemia.

Find out about the Full Blood Count

Blood film examination (smear). In this test a thin stained layer of blood is examined on a slide, under a microscope. The number and type of white blood cells, red blood cells, and platelets can be manually counted and be evaluated to see if they are normal and mature. A variety of disorders affect normal blood cell production. With thalassaemia, the red blood cells are often microcytic (small) with a low MCV. They may also be:

  • Hypochromic (pale – indicating less haemoglobin than normal)
  • Vary in size (anisocytosis) and shape (poikilocytosis)
  • Be nucleated (not normal in a mature RBC)
  • Be distorted to produce “target cells”, which look like a bull’s-eye under the microscope.

Iron studies. These may include: iron, ferritin, UIBC, TIBC, and percent saturation of transferrin. These tests measure different aspects of the body’s iron storage and usage. They are ordered to help determine whether an iron deficiency is causing and/or exacerbating a patient’s anaemia. One or more of them may also be ordered to help monitor the degree of iron overload in a patient with thalassaemia.

Haemoglobinopathy (Hb) evaluation. This test measures the type and relative amounts of haemoglobins present in the red blood cells. Haemoglobin A, composed of both alpha and beta globin, is the major normal type of haemoglobin found in adults. A greater percentage of HbA2 and/or HbF is usually seen in beta thalassaemia trait. HbH may be seen in alpha thalassaemia, but only when at least two of the four alpha genes are deleted or mutated.

DNA analysis. In many cases DNA analysis is not required because the diagnosis can be made from the results of the above tests. DNA analysis is most commonly used in families affected by alpha-thalassaemia. This test is used to investigate deletions and mutations in the alpha and less commonly the 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 an important tool in establishing an accurate diagnosis of thalassaemia. In particular in alpha thalassaemia it is important to know if a person with alpha thalassaemia trait has two mutated genes on one chromosome or one on each chromosome. DNA analysis is also the only reliable way of diagnosing carriers who have only one of four alpha genes deleted or mutated and who have normal haemoglobin and red cells in the basic blood tests.

For more on inheritance of thalassaemias see this NSW Health Genetics Education Fact Sheet.

Last Review Date: November 23, 2018