Alpha Globin (HBA1 and HBA2) Sequencing
2001582
Ordering Recommendation
Second-tier genetic test for detection of alpha thalassemia. Order if suspicion of alpha thalassemia remains in spite of negative molecular HBA1 and HBA2 gene deletion testing.
Mnemonic
AG FGS
Methodology
Polymerase Chain Reaction/Sequencing
Performed
Varies
Reported
Within 21 days  
New York DOH Approval Status
Specimens from New York clients will be sent out to a New York DOH approved laboratory, if possible.
Specimen Required
Patient Preparation
  
Collect
Contact ARUP's genetic counselor at (800) 242-2787 extension 2141 prior to test submission for collection requirements.  
Specimen Preparation
Transport 3 mL whole blood. (Min: 1 mL)  
Storage/Transport Temperature
Refrigerated.  
Unacceptable Conditions
  
Remarks
  
Stability
Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable  
Reference Interval
   
Interpretive Data
Background Information for Alpha Globin (HBA1 and HBA2) Sequencing:
Characteristics:
Alpha thalassemia, caused by insufficient or absent alpha chain production, has a highly variable clinical presentation. Classic deletional alpha thalassemia is not detected by sequencing; deletional subtypes include:
Alpha thalassemia silent carrier: deletion of a single alpha globin gene (-a/aa); typically asymptomatic.
Alpha thalassemia trait: deletion of two alpha globin genes in trans (-a/-a), or cis (--/aa); mild microcytic anemia possible.
Hemoglobin H disease; deletion of three alpha globin genes (--/-a); hemolysis with Heinz bodies, moderate anemia, splenomegaly.
Hemoglobin Bart hydrops fetalis syndrome; deletion of four alpha globin genes (--/--); lethal in fetal or early neonatal period.
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:
High carrier frequency in Mediterranean (1 in 30 to 1 in 50), Middle Eastern, Southeast Asian (1 in 20), African and African-American (1 in 3) populations.
Inheritance:
Autosomal recessive.
Cause
: Pathogenic HBA1 or HBA2 gene mutations.
Clinical Sensitivity:
Up to 10 percent for sequencing. Most pathogenic HBA1 and/or HBA2 gene mutations are large deletions not detectable by sequencing.
Methodology:
Bidirectional sequencing of theHBA1 and HBA2 coding regions, intron-exon boundaries, proximal promoter regions, 5' and 3' untranslated regions, and polyadenylation signals.
Analytical Sensitivity and Specificity:
99 percent.
Limitations:
Diagnostic errors can occur due to rare sequence variations. Large deletions/duplications and some mutations of the regulatory regions, will not be detected. The phase of identified mutations may not be determined. This test is not able to identify sequence variants in an alpha globin gene in cis with the common 3.7 kb deletion. Therefore, sequencing is not possible in individuals homozygous for the 3.7 kb deletion; individuals heterozygous for the 3.7 kb deletion will appear homozygous for sequence variants present on the non-deleted allele. Rare syndromes associated with alpha thalassemia, such as ATR-X and ATR-16, will not be detected.





See Compliance Statement C: www.aruplab.com/CS
Statement C: The performance characteristics of this test were validated by ARUP Laboratories. The U.S. Food and Drug Administration (FDA) has not approved or cleared this test; however, FDA approval or clearance is currently not required for clinical use of this test. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions. ARUP is authorized under Clinical Laboratory Improvement Amendments (CLIA) and by all states to perform high-complexity testing.

Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
 
Note
For detection of the seven most common deletions, refer to Alpha Thalassemia, HBA1 & HBA2 Gene Deletions (0051495).
CPT Code(s)
81405
Components
Component Test Code*Component Chart NameLOINC
2001583Alpha Globin (HBA) Sequencing Specimen31208-2
2001585Alpha Globin (HBA) Sequencing Interp 
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
Aliases
  • A globin sequencing
  • Alpha Globin
  • HBA1, HBA2 sequencing