Sign in →

Test Code WBSEQ Beta Globin Gene Sequencing, Blood

Secondary ID

62128

Useful For

Diagnosis of beta thalassemia intermedia or major

 

Identification of a specific beta thalassemia mutation (ie, unusually severe beta thalassemia trait)

 

Evaluation of an abnormal hemoglobin electrophoresis identifying a rare beta globin variant

 

Evaluation of chronic hemolytic anemia of unknown etiology

 

Evaluation of hereditary erythrocytosis with left-shifted p50 oxygen dissociation results

 

Preconception screening when there is a concern for a beta hemoglobin disorder based on family history

Testing Algorithm

This is a second-tier evaluation of beta thalassemia minor, intermedia, and major, as well as beta globin variant identification.

 

First-tier testing for beta thalassemia or beta globin variant detection is THEVP / Thalassemia and Hemoglobinopathy Evaluation or HBELC / Hemoglobin Electrophoresis Cascade, Blood.

Method Name

Polymerase Chain Reaction (PCR) followed by DNA Sequence Analysis

Reporting Name

Beta Globin Gene Sequencing, B

Specimen Type

Whole Blood EDTA


Advisory Information


For information on thalassemias and appropriate test ordering, see Thalassemia Tests in Special Instructions.



Necessary Information


1. Patient’s age is required.

2. Include recent transfusion information.



Specimen Required


Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: ACD, sodium heparin

Specimen Volume: 3 mL

Collection Instructions: Do not transfer blood to other containers


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Refrigerated 14 days

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

Moderately to severely clotted

Clinical Information

Beta globin gene sequencing is useful in the evaluation of beta globin chain variants and beta thalassemia. It detects almost all beta globin variants and the most common beta thalassemia mutations, although prevalence is ethnicity-dependent. Because these conditions are often complex, this test should always be interpreted in the context of protein studies, such as hemoglobin electrophoresis and RBC indices.

 

The majority of beta globin chain variants are clinically and hematologically benign; however, some have important clinical consequences, such as erythrocytosis, cyanosis/hypoxia, chronic hemolysis, or unexplained microcytosis. Most of the common clinically significant hemoglobin (Hb) variants (ie, Hb S, Hb C, Hb E, and others) are easily distinguished by hemoglobin electrophoresis and do not require molecular analysis. In addition, they are frequently found in complex hemoglobin disorders due to multiple mutations, and accurate classification requires sequencing data within the context of protein data. In some instances, beta globin sequencing is necessary to identify or confirm the identity of rare variants, especially those associated with erythrocytosis and chronic hemolytic anemia. Rare hyperunstable variants (also termed dominant beta thalassemia mutations) result in hemolytic anemia and do not create protein stable enough to be detectable by protein methods, including stability studies. They are not always associated with elevated Hb A2 or microcytosis and, therefore, can be electrophoretically silent. These require a high degree of clinical suspicion as all electrophoretic testing as well as stability studies cannot exclude this condition.

 

Beta thalassemia is an autosomal recessive condition characterized by decreased or absent synthesis of beta globin chains due to mutations in the beta globin gene (HBB). No abnormal protein is present and diagnosis by electrophoresis relies on hemoglobin fraction percentage alterations (ie, Hb A2 or Hb F elevations).

 

Beta thalassemia can be split into 3 broad classes (categorized by clinical features)

1. Beta thalassemia trait (also called beta thalassemia minor and beta thalassemia carrier) (B[A]B[+] or B[A]B[0]).

2. Beta thalassemia intermedia (B[+]B[+] or B[+]B[0])

3. Beta thalassemia major (B[+]B[0] or B[0]B[0])

 

Beta thalassemia trait is typically a harmless condition with varying degrees of microcytosis and hypochromia and sometimes mild anemia. Transfusions are not required. Beta thalassemia intermedia is a clinical distinction and is characterized by a more severe degree of anemia than beta thalassemia trait with few or intermittent transfusions required. Later in life, these individuals are at risk for iron overload even in the absence of chronic transfusion due to increased intestinal absorption of iron. Beta thalassemia major typically comes to medical attention early in life due to severe anemia, hepatosplenomegaly, and failure to thrive. Skeletal changes are also common due to expansion of the bone marrow. Without appropriate treatment these patients have a shortened lifespan.

 

The majority of beta thalassemia mutations (>90%) are point mutations, small deletions, or insertions, which are detected by beta globin gene sequencing. The remaining beta thalassemia mutations are either due to large genomic deletions of HBB or, very rarely, trans-acting beta thalassemia mutations located outside of the beta globin gene cluster. Some rare beta chain variants can be clinically or electrophoretically indistinguishable from beta thalassemia and cannot be confirmed without molecular analysis.

Reference Values

An interpretive report will be provided.

Interpretation

The alteration will be provided with the classification, if known. Further interpretation requires correlation with protein studies and RBC indices.

Clinical Reference

1. Hoyer JD, Hoffman DR: The thalassemia and hemoglobinopathy syndromes. In Clinical Laboratory Medicine. Second edition. Edited by KD McClatchey. Philadelphia, Lippincott Williams and Wilkins, 2002, pp 866-895

2. Thein SL: The Molecular Basis of Beta-Thalassemia. Cold Spring Harb Persepct Med 2013;1;3(5):a011700

3. Hoyer JD, Kroft, SH: Color Atlas of Hemoglobin Disorders: A Compendium Based on Proficiency Testing. Northfield, IL. CAP, 2003

4. Merchant S, Oliveira JL, Hoyer JD, Viswanatha DS: Molecular diagnosis in hematopathology. In Hematopathology: A Volume in Foundations in Diagnostic Pathology Series. Second edition Edited by J Goldblum.  Volume Editor E Hsi. Churchill Livingstone, 2012

Day(s) and Time(s) Performed

Monday, Wednesday, Friday

Analytic Time

2 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81404-HBB (hemoglobin, beta) full sequence

LOINC Code Information

Test ID Test Order Name Order LOINC Value
WBSEQ Beta Globin Gene Sequencing, B 79401-6

 

Result ID Test Result Name Result LOINC Value
62128 Beta Globin Gene Sequencing, B 79401-6
43922 Interpretation 69047-9

Forms

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. Thalassemia/Hemoglobinopathy Patient Information (T358) in Special Instructions.