Alpha-thalassemia

Diagnosis and Testing

How do I get tested for alpha-thalassemia?

Alpha-thalassemia can be diagnosed by blood analysis. Genetic testing can also be performed to determine the exact changes to the genes involved, HBA1 and HBA2.

Blood testing involves analysis of the size, shape, color and number of red blood cells and is called a complete blood count, or CBC. The hemoglobin is also analyzed to determine how much and which types of hemoglobin are present. The best test for detecting the abnormal hemoglobin of alpha-thalassemia is called high performance liquid chromatography (HPLC) or electrophoresis.

An analysis of red blood cells will show that affected individuals will have blood cells that are unusually shaped, lighter in color, and an increased number of immature blood cells.

People with the most severe form, hemoglobin Bart, will have enlarged red blood cells and an increased amount of hemoglobin in cells. Those with less severe alpha-thalassemia have decreased red blood cell size, a decreased amount of hemoglobin in each red blood cell, and inclusion bodies, which are clumps of abnormal hemoglobin, in the red blood cells.

An analysis of hemoglobin will reveal the presence of abnormal hemoglobin, including hemoglobin Bart in those with hemoglobin Bart syndrome, and hemoglobin H in those with hemoglobin H disease. The presence of a normal level of a type of hemoglobin called hemoglobin A2 would rule out a similar condition, beta-thalassemia, which normally has an increased level of hemoglobin A2. Iron deficiency also must be ruled out since iron deficiency can mimic alpha-thalassemia.

Genetic testing can determine the specific changes of the genes involved, HBA1 and HBA2. Understanding the exact changes involved with these genes will enable more accurate prediction of the severity of the disease and better manage symptoms. DNA testing also allows the health care provider to provide an accurate risk of future pregnancies being affected. Genetic testing is necessary if parents are concerned about a pregnancy being affected and want to have prenatal genetic testing. People who are carriers of alpha-thalassemia may not have symptoms or abnormal blood testing and can only be detectable by genetic testing.

90% of changes to the HBA1 and HBA2 genes are deletions of pieces of the gene. 10% are small changes to just one 'letter' of the gene. It is important to keep in mind that a patient can have more than one type of hemoglobin disease and having a diagnosis of alpha-thalassemia does not rule out having other hemoglobin diseases.

Diagnosis can be made early in a pregnancy with a procedure called chorionic villus sampling (CVS). Because of the complexity of the inheritance of alpha-thalassemia, testing and interpretation of test results is best performed by genetic professionals, including genetic counselors. Genetic counselors can be found on the National Society of Genetic Counselors website.

Origa, R., Moi, P., Galanello, R., & Cao, A. (2013). Alpha-Thalassemia. GeneReviews at GeneTests Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2013. Available at http://www.genetests.org. Accessed (2/29/2016).

Piel, F. & Weatherall, D. (2014). The alpha-thalassemias. The New England Journal of Medicine, 1908-1916. doi: 10.1056/NEJMra1404415

Vichinsky, E. (2012). Advances in the treatment of alpha-thalassemia. Blood Reviews, S31-S34. http://www.sciencedirect.com/science/article/pii/S0268960X12700103

Standard-of-care clinical practice guidelines. (2012). UCSF Benioff Children's Hospital. Northern California Comprehensive Thalassemia Center. Retrieved from http://thalassemia.com/treatment-guidelines-20.aspx#gsc.tab=0

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