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 (-a/aa); asymptomatic. Alpha (0) thalassemia (trait): Mutation of both alpha2 globin genes, or deletion of alpha1 and alpha2 globin genes in cis (-a/-a;--/aa); mild microcytic anemia possible. Hemoglobin H disease: Mutation of three alpha globin genes (--/-a); 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: -a3.7,-a4.2,-(a)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.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|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