Hemoglobin (Hb) A2, Quantitative

CPT: 83021
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Test Details

Synonyms

  • A2, Quantitative
  • Hb A2, Quantitative

Use

Investigate for hemolytic anemia, hemoglobinopathies, and thalassemia

Limitations

Blood transfusion prior to hemoglobin analysis may cause inconsistent interpretation.

Methodology

High-pressure liquid chromatography (HPLC)

Reference Interval

See table.

Age

Percentage

<7 mo

Not established

7 mo to 1 y

1.9% to 2.8%

≥2 y

1.8% to 3.2%

Additional Information

Hemoglobin A2 levels have special application to the diagnosis of β-thalassemia trait, which may be present even though peripheral blood smear is normal. (This reflects the underlying genetic spectrum of β-thalassemia, which in reality is a complex of 20 to 30 distinct conditions.) The microcytosis and other morphologic changes of beta-thalassemia trait must be differentiated from iron deficiency. Low MCV may include the majority of β-thalassemia trait patients but does not differentiate iron deficient individuals. Low Hb A2 levels occur in untreated iron deficiency. If the β-thalassemia is associated with iron deficiency, the Hb A2 level falls, making the differentiation even more difficult (corrected after iron therapy).1 The most definitive evidence for presence of β-thalassemia trait is genetic (family study). Offspring of a person with thalassemia major will have beta-thalassemia trait. Hb A2 may be increased in megaloblastic anemia and may be decreased in sideroblastic anemia, Hb H disease, and erythroleukemia.

Specimen Requirements

Specimen

Whole blood

Volume

1 mL

Minimum Volume

0.5 mL

Container

Lavender-top (EDTA) tube, blue-top (sodium citrate) tube, or green-top (heparin) tube

Patient Preparation

Fasting or fluid restriction is not necessary.

Collection

Pediatric: heelstick. To avoid delays in turnaround time, please submit a separate lavender-top tube for each test requiring a lavender-top.

Storage Instructions

Refrigerated specimens may be stored at 4°C for seven days. Do not store as hemolysate.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Clotted specimen

Clinical Information

Special Instructions

Specify on the request form the patient's race or ethnic origin (if known) as well as the date of any transfusions administered within the preceding three months.

Footnotes

1. Wasi P, Disthasongchan P, Na-Nakorn S. The effect of iron deficiency on the levels of hemoglobins A2 and E. J Lab Clin Med. 1968 Jan; 71(1):85-91. 5635011

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
121020 Hgb A2, Quant 34660-1 121705 Hgb A2 % 34660-1

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