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Test ID: A2F    
Hemoglobin A2 and F, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Assisting in the diagnosis of beta-thalassemia

 

Quantitating the percent of hemoglobin F (Hgb F) present

 

Assisting in the diagnosis of disorders with elevated levels of Hgb F

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Hemoglobin F (Hgb F), composed of 2 alpha and 2 gamma globin chains, is the normal hemoglobin of the fetus and newborn. Normally in the second trimester, gamma chain production (and Hgb F levels) decrease and beta chain production increases, resulting in increasing levels of Hgb A, the major normal adult Hgb (2 alpha and 2 beta globin chains). Hgb A2 (2 alpha and 2 delta globin chains) also comprises a small amount (<3.3%) of Hgb normally found in adults. Hgb A2 values at birth are <1%.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

HEMOGLOBIN A2

1-30 days: 0.0-2.1%

1-2 months: 0.0-2.6%

3-5 months: 1.3-3.1%

> or =6 months: 2.0-3.3%

 

HEMOGLOBIN F

1-30 days: 22.8-92.0%

1-2 months: 7.6-89.8%

3-5 months: 1.6-42.2%

6-8 months: 0.0-16.7%

9-12 months: 0.0-10.5%

13-17 months: 0.0-7.9%

18-23 months: 0.0-6.3%

> or =24 months: 0.0-0.9%

Interpretation Provides information to assist in interpretation of the test results

Hemoglobin A2 (Hgb A2) values of 3.5% to 9% are found in beta-thalassemia trait.

 

In beta-thalassemia major, hemoglobin F (Hgb F) may be 30% to 90% or even more of the total hemoglobin.

 

Hgb F concentration is usually between 5% to 15% of the total hemoglobin in delta/beta-type thalassemia trait (F-thalassemia).

 

Higher concentrations of Hbg F occur in hemoglobin S (Hgb S)/beta zero-thalassemia, in patients who are doubly heterozygous for the Hgb S gene, and in patients who have a gene for hereditary persistence of fetal hemoglobin (HPFH). These disorders may be differentiated by family studies or by flow cytometry studies for Hgb F (HPFH/8270 Hemoglobin F, Red Cell Distribution, Blood), which reveals uniform intraerythrocytic distribution of Hgb F in HPFH and nonuniform distribution in Hgb S/beta thalassemia.

 

The electrophoretic finding of small quantities of Hgb A in a patient who has mostly Hgb S and a moderate increase in Hgb F is strong evidence of Hgb S/beta thalassemia (if the patient has not had a transfusion).

 

Hgb F values greater than normal (2%) may be seen in chronic anemias, beta-thalassemia, and HPFH

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Hemoglobin F (Hgb F) is elevated in newborns, reaching adult levels by 12 months.

 

Hgb F is commonly increased to as much as 5% to 10% in normal pregnancy.

 

Slight elevation in hemoglobin A2 may also occur in hyperthyroidism or when there is deficiency of vitamin B12 or folate.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

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

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test