Diagnostic Algorithm for Thalassemia

Defective Production	Thalassemia Type
alpha globin	alpha
beta globin	beta
delta and beta globins	delta-beta

 

Thalassemia may occur with:

(1) deletion of the entire globin gene (chromosome 16 for alpha gene, chromosome 11 for beta gene)

(2) small mutations within critical portions of the globin gene that prevent translation into protein

(3) hemoglobin variants (such as Hemoglobin Lepore) with defective production of abnormal globin chains

 

Abnormal tetramers in thalassemia:

(1) hemoglobin H: tetramer of 4 beta globin chains

(2) hemoglobin Barts: tetramer of 4 delta globin chains (hemoglobin F is composed of 2 alpha and 2 delta chains)

 

Screening panel for patients with microcytosis and possible thalassemia:

(1) serum ferritin level initially

Once any iron deficiency has been corrected, then perform

(2) quantitation of hemoglobins A2 and F

(3) hemoglobin electropheresis

(4) hemoglobin H inclusion body screen

 

Hemoglobin A2	Diagnosis
1.5 – 3.5% of total hemoglobin	normal, or mixed iron deficiency and beta thalassemia
4.0 – 8.0%	beta-thalassemia
> 10%	hemoglobin E, hemoglobin C, or hemoglobin O (co-elute with hemoglobin A2)

 

Hemoglobin electropheresis (alkaline pH, acid pH) can identify abnormal hemoglobins (E, Lepore, Constant Spring, H, etc.).

 

Hemoglobin H inclusion body screen:

(1) Examine the Wright stained blood smear to exclude intra-erythrocytic inclusions

(2) 6 drops of blood are mixed with 1 drop of supravital stain (brilliant cresyl blue, new methylene blue) and incubated at 37°C for exactly 1 hour

(3) Smears of sample examined for round, globular, peacock blue bodies within erythrocytes

 

Hemoglobin F	Hemoglobin H Inclusion Bodies	Diagnosis
5.0 – 15%	negative	delta-beta thalassemia trait
normal (0 - 2%)	numerous	hemoglobin H disease
normal (0 - 2%)	negative or occasional	alpha thalassemia trait

 

Confirmatory testing:

(1) alpha thalassemia trait: DNA genotype for alpha globin gene

 

Other conditions to consider once iron deficiency and thalassemia are excluded:

(1) anemia of chronic disease

(2) congenital sideroblastic anemia