Acceptable first-tier genetic test for confirmation of suspected alpha thalassemia or alpha thalassemia trait. Assesses for seven common alpha globin gene deletions.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable
Characteristics: Alpha (+) thalassemia (silent carrier): Mutation of a single alpha2 globin gene (-α/αα); asymptomatic. Alpha (0) thalassemia (trait): Mutation of both alpha2 globin genes, or deletion of alpha1 and alpha2 globin genes in cis (-α/-α;--/αα); mild microcytic anemia possible. Hemoglobin H disease: Mutation of three alpha globin genes (--/-α); hemolysis with Heinz bodies, moderate anemia, and splenomegaly. Hb Bart Hydrops Fetalis Syndrome: Mutation of four alpha globin genes (--/--); lethal in fetal or early neonatal period.
Incidence: Carrier frequency in Mediterranean (1:30-50), Middle Eastern, Southeast Asian (1:20), African, African-American (1:3).
Inheritance: Autosomal recessive.
Cause: Mutations in the alpha globin gene cluster; 95 percent are deletions.
Mutations Tested: -α3.7,-α4.2,-(α)20.5,--SEA,--MED,--FIL,--THAI
Clinical Sensitivity: Varies by ethnicity, may be as high as 90 percent.
Methodology: Polymerase chain reaction and gel electrophoresis.
Analytical Sensitivity and Specificity: Greater than 99 percent.
Limitations: Rare alpha globin gene deletions, non-deletion mutations, gene duplications, and mutations of the regulatory region will not be detected. Diagnostic errors can occur due to rare sequence variations.
|Component Test Code*||Component Chart Name||LOINC|
|0051501||Alpha Thalassemia, 7 Deletions||66502-6|
|2001293||Alpha Thalassemia, Specimen||31208-2|
- alpha globin mutation deletions
- HBA1, HBA2