Whole Blood

Preferred Minimum: 3 mL whole blood
Absolute Minimum: 2 mL whole blood

14-21 days upon receipt at reference laboratory

Characteristics: Alpha thalassemia is caused by decreased or absent synthesis of the hemoglobin alpha-chain resulting in variable clinical presentations. Alpha (+) thalassemia results from mutation of a single alpha2 globin gene (-/) and is clinically asymptomatic (silent carrier). Alpha (0) thalassemia (trait) is caused by mutation of both alpha2 globin genes (-/-), or mutations in the alpha1 and alpha2 globin genes on the same chromosome, (--/) and results in mild microcytic anemia. Hemoglobin H disease occurs due to mutation of three alpha globin genes (--/-) and results in hemolysis with Heinz bodies, moderate anemia, and splenomegaly. Hb Bart Hydrops Fetalis Syndrome results when mutations occur in all four alpha globin genes (--/--) and is lethal in the fetal or early neonatal period. Alpha globin gene triplications result in three active alpha globin genes on a single chromosome. Non- deletional alpha globin mutations may be pathogenic or benign; both may result in an abnormal protein detectable by hemoglobin evaluation. Pathogenic non-deletional mutations often have a more severe effect than single gene deletions.

Incidence: Carrier frequency in Mediterranean (1:30- 50), Middle Eastern, Southeast Asian (1:20), African, African-American (1:3).

Inheritance: Autosomal recessive.

Cause: Pathogenic mutations in the alpha globin gene cluster.

Clinical Sensitivity: 99 percent.

Methodology: Bidirectional sequencing of the HBA1 and HBA2 coding regions, intron-exon boundaries, proximal promoter regions, 5' and 3' untranslated regions, and polyadenylation signals. Multiplex ligation-dependent probe amplification (MLPA) of the alpha globin gene cluster (HBZ, HBM, HBA1, HBA2, HBQ1) and its HS-40 regulatory region.

Analytical Sensitivity and Specificity: 99 percent.

Please submit a recent CBC and print, complete, and submit the Patient History for Hemoglobinopathy/Thalassemia Testing from ARUP Laboratories with the specimen and the Epic Req.

Diagnostic errors can occur due to rare sequence variations. Sequence analysis will not detect all regulatory region variants or variants in alpha globin cluster genes other than HBA1 and HBA2. Sequencing of both HBA1 and HBA2 may not be possible in individuals harboring large alpha globin deletions on both alleles. This assay is unable to sequence HBA2-HBA1 fusion genes; thus, HBA1 or HBA2 sequence variants occurring in cis with a 3.7 kb deletion or other HBA2-HBA1 hybrid gene will not be detected (e.g., HbG Philadelphia will not be detected when in cis with the 3.7 kb deletion). It may not be possible to determine phase of identified sequence variants. Specific breakpoints of large deletions/duplications will not be determined; therefore, it may not be possible to distinguish variants of similar size. Individuals carrying both a deletion and duplication within the alpha globin gene cluster may appear to have a normal number of alpha globin gene copies. Rare syndromic or acquired forms of alpha thalassemia associated with ATRX variants will not be detected.

Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification.

HBA1 and HBA2 Sequencing - 81259
HBA1 and HBA2 Deletion/Duplication - 81269