MLAB 1415: Hematology Keri Brophy-Martinez Thalassemia Part Two: Alpha Thalassemia

Alpha Thalassemia Predominant cause of alpha thalassemias is large number of gene deletions in the alpha-globin gene. Four types in alpha thalassemia: Silent Carrier State Alpha Thalassemia Trait  (Alpha Thalassemia Minor) Hemoglobin H Disease Bart's Hydrops Fetalis Syndrome

Hemoglobin H Disease Second most severe form alpha thalassemia. Only one alpha gene out of four is functional Results in accumulation of excess unpaired gamma or beta chains. The excess chains pair up to form tetrads Beta: hemoglobin H (adults) Gamma: hemoglobin Bart’s (infants) Unstable Precipitates within RBCs triggers hemolysis High affinity for oxygen which reduces oxygen delivery to the tissues

Laboratory Findings: Hemoglobin H Disease RBCs are microcytic, hypochromic with marked poikilocytosis.  Numerous target cells.

Bart’s Hydrops Fetalis Syndrome or α-Thalassemia major Have no functioning alpha chain genes Baby born with Hydrops Fetalis, which is edema and ascites caused by accumulation of serous fluid in fetal tissues as result of severe anemia.  Hepatosplenomegaly and cardiomegaly are present Pregnancies dangerous to mother.  Increased risk of toxemia and severe postpartum hemorrhage.

Bart’s Hydrops Fetalis Syndrome Predominant hemoglobin is Hemoglobin Bart, along with Hemoglobin Portland and traces of Hemoglobin H. Hemoglobin Bart's has high oxygen affinity so cannot carry oxygen to tissues.  Fetus dies in utero or shortly after birth.

Laboratory Diagnosis of Thalassemia

Laboratory Diagnosis of Thalassemia Need to start with patient's individual history and family history.  Ethnic background important. Perform physical examination: Pallor indicating anemia. Jaundice indicating hemolysis. Splenomegaly due to pooling of abnormal cells. Skeletal deformity, especially in beta thalassemia major.

CBC with Differential Differential Decreased Hemoglobin, hematocrit Mean corpuscular volume (MCV) Mean corpuscular hemoglobin (MCH) Normal to slightly decreased Mean Corpuscular Hemoglobin Concentration (MCHC) Have normal or elevated RBC count with a normal red cell volume distribution (RDW). Elevated RBC count with markedly decreased MCV differentiates thalassemia from iron deficiency anemia Differential Microcytic, hypochromic RBCs (except in carrier states) Mild to moderate poikilocytosis In more severe cases, see marked number of target cells and elliptocytes,polychromasia, basophilic stippling, and NRBCs.

Other Hematology Tests Reticulocyte Count Usually elevated.  Degree of elevation depends upon severity of thalassemia. Osmotic Fragility Have decreased osmotic fragility. Is not very useful fact for diagnosing thalassemia.  Is an inexpensive way of screening for carrier states.

Brilliant Cresyl Blue Stain Incubation with brilliant cresyl blue stain causes Hemoglobin H to precipitate.  Results in characteristic appearance of multiple discrete inclusions -golf ball appearance of RBCs.   Inclusions smaller than Heinz bodies and are evenly distributed throughout cell.

Acid Elution Stain Based on Kleihauer-Betke procedure. Acid pH will dissolve Hemoglobin A from red cells.  Hemoglobin F is resistant to denaturation and remains in cell.  Stain slide with eosin.  Normal adult cells appear as "ghost" cells while cells with Hb F stain varying shades of pink.

Hemoglobin Electrophoresis Important role in diagnosing and differentiating various forms of thalassemias. Can differentiate among Hb A, Hb A2, and Hb F, as well as detect presence of abnormal hemoglobins such as Hemoglobin Lepore, hemoglobin Bart's, or Hemoglobin Constant Spring. Also aids in detecting combinations of thalassemia and hemoglobinopathies.

Hemoglobin Quantitation Elevation of Hb A2 excellent way to detect heterozygote carrier of beta thalassemia.  Variations in gene expression in thalassemias results in different amounts of Hb A2 being produced. Can also quantitate levels of Hb F.

Routine Chemistry Tests Indirect bilirubin elevated in thalassemia major and intermedia. Assessment of iron status, total iron binding capacity, and ferritin level important in differentiating thalassemia from iron deficiency anemia.

Differential Diagnosis of Microcytic, Hypochromic Anemias RDW Serum Iron TIBC Serum Ferritin Iron Deficiency Inc Dec Alpha Thal Norm Beta Thal Hgb E Disease Anemia of Chronic Inflammation Sideroblastic Anemia Lead Poisoning

References Harmening, D. M. (2009). Clinical Hematology and Fundamentals of Hemostasis. Philadelphia: F.A Davis. McKenzie, S. B., & Williams, J. L. (2010). Clinical Laboratory Hematology . Upper Saddle River: Pearson Education, Inc. http://prepgmedicos.redstetho.com/forum/viewtopic.ph p?f=88&t=5166&start=0