ARUP's Laboratory Test Directory

Alpha Thalassemia (HBA1 & HBA2) Sequencing : 2001582
[ image for: Patient History for Hemoglobinopathy]
Patient History for Hemoglobinopathy
  


Mnemonic: AG FGS

Methodology: Polymerase Chain Reaction/Sequencing 
Performed: Varies
Reported: Within 21 days
Specimen Required: Collect:  One 3 mL whole blood in lavender (EDTA), pink (K2EDTA) or yellow (ACD Solution A or B) tube.

Transport:  3 mL whole blood at 2-8°C. (Min: 1 mL)

Stability:  Ambient: 3 days; Refrigerated: 1 week; Frozen: Unacceptable
Interpretive Data: Background Information for Alpha Thalassemia (HBA1 & HBA2) Sequencing:
Characteristics:
Alpha thalassemia, caused by insufficient or absent alpha chain production, has a highly variable clinical presentation. Classic deletional alpha thalassemia may result in:
Alpha thalassemia silent carrier; mutation of a single alpha globin gene (-a/aa); typically asymptomatic.
Alpha thalassemia trait; mutation of two globin genes in trans (-a/-a), or cis ( --/aa); mild microcytic anemia possible.
Hemoglobin H disease; mutation of three alpha globin genes (--/-a); hemolysis with Heinz bodies, moderate anemia, splenomegaly.
Hemoglobin Bart hydrops fetalis syndrome; mutation of four alpha globin genes (--/--); lethal in fetal or early neonatal period.
Non-deletional alpha thalassemia may result in more severe phenotypes.
Incidence:
Carrier frequency in Mediterranean (1 in 30 to 1 in 50), Middle Eastern, Southeast Asian (1 in 20), African, African-American (1 in 3).
Inheritance:
Autosomal recessive.
Cause
: Deleterious HBA1 or HBA2 gene mutations.
Clinical Sensitivity:
Up to 10 percent. Most HBA1 and/or HBA2 gene mutations are large deletions not detectable by sequencing.
Methodology:
Bidirectional sequencing of the entire HBA1 and HBA2 coding region and intron-exon boundaries, proximal promoter region, 5' and 3' untranslated regions, and polyadenylation signal.
Analytical Sensitivity and Specificity:
99 percent.
Limitations:
Rare diagnostic errors can occur due to primer site mutations. Large deletions/duplications and some mutations of the regulatory regions, will not be detected. Phase of identified mutations may not be determined. Rare syndromes associated with alpha thalassemia such as ATR-X and ATR-16 will not be detected.





Please refer to Statement C in the Compliance Statements section in the front of the Laboratory Test Directory.
Note: For detection of the seven most common deletions, refer to Alpha Thalassemia, HBA1 & HBA2 Gene Deletions (0051495).
CPT Code(s): 83891 Isolation; 83898 x2 Amplification; 83904 x6 Sequencing; 83909 capillary electrophoresis; 83912 Interpretation and report - Additional CPT code modifiers may be required for procedures performed to test for oncologic or inherited disorders.
 
 

 

 

 
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