β-Thalassemia: HBB (Full Gene Sequencing)

CPT: 81364
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Test Details

Test Includes

This test covers all coding nucleotides of gene HBB, plus at least two and typically 20 flanking intronic nucleotides upstream and downstream of each coding exon, covering the conserved donor and acceptor splice sites, as well as typically 20 flanking nucleotides in the 5′ and 3′ UTR.

Use

Confirm a clinical diagnosis of β-thalassemia; detect carriers; help to establish a prognosis

Limitations

This method does not reliably detect mosaic variants; large deletions; large duplications, inversions, or other rearrangements; or deep intronic variants. It may be affected by allele-dropout; it may not allow determination of the exact numbers of T/A or microsatellite repeats; and it does not allow any conclusion as to whether two heterozygous variants are present on the same or on different chromosome copies.

Methodology

DNA sequencing

Reference Interval

Normal equals reference sequence or variants that are known or predicted to be benign; abnormal equals all other variants.

Additional Information

β-Thalassemia is a typically autosomal-recessive form of severe anemia. Prevalence is estimated at 1:100,000 worldwide and at 1:10,000 in the European Union, reflecting the increased prevalence in Mediterranean populations. Based on disease severity, three types of β-thalassemia are distinguished: β-thalassemia major (also known as Cooley's anemia), β-thalassemia intermedia, and β-thalassemia minor (also known as β-thalassemia trait). β-Thalassemia minor is mostly asymptomatic, but may be accompanied by mild anemia. In contrast, β-thalassemia major is characterized by infancy-onset severe anemia and requires life-long blood transfusions for survival. By definition, the intermediate form requires only intermittent blood transfusions for survival. Bone marrow or cord blood transplantation offers a cure, especially if performed before lasting organ damage has developed. Early diagnosis is, therefore, crucial to allow timely treatment initiation. Distinction between the intermediate and major forms is also important to avoid both unnecessary transfusions and unnecessary delay of required regular transfusions, which can increase the risk that the patient may develop multiple antibodies against donor red blood cells. Genetic testing can help with this diagnosis, since severity of β-thalassemia can partially be predicted from the nature of the causative mutations in HBB, the gene coding for β-globin. In addition, genetic testing can also identify mutations associated with rare cases of dominantly inherited β-thalassemia. Once the mutations causing β-thalassemia in a specific family have been identified, genetic testing for these mutations can also help to diagnose affected siblings of patients prenatally or directly after birth and facilitate genetic counseling in other relatives.

Specimen Requirements

Specimen

Whole blood; DNA is accepted (Call 800-345-4363 for DNA collection information.)

Volume

2 mL

Container

Lavender-top (EDTA) tube

Collection

Samples may be stored for brief periods at 4°C. Ship overnight at room temperature.

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Container broken or leaking; container not labeled or label not legible; use of improper anticoagulant

Clinical Information

Special Instructions

In cases in which a known mutation can be documented, the physician may prefer to order test 252827.

Test orders must include an attestation that the provider has the patient's informed consent for genetic testing. See sample physician office consent form: Consent for Genetic Testing. In the case of family tests (ie, known mutations), please submit the result report of the first patient tested in the family (the index case), if not performed at a LabCorp facility. Other family members are subsequently tested for the specific mutation found in the first patient tested.

References

Cao A, Galanello R. Beta-Thalassemia. GeneReviews. 2010. Available at: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=b-thal. Accessed August 1, 2010. 20301599
Galanello R, Origa R. Beta-thalassemia. Orphanet J Rare Dis. 2010 May 21; 5:11. 20492708
Thein SL. Genetic modifiers of beta-thalassemia. Haematologica. 2005 May; 90(5):649-660. 15921380

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
252823 Beta Thalassemia: HBB 21689-5 252211 Routing 21689-5

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The LOINC® codes are copyright © 1994-2018, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf