Hemoglobin A2 and F, Blood
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Hemoglobin F (Hb 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 hemoglobin A (Hb A), the major normal adult hemoglobin (2 alpha and 2 beta globin chains). Hemoglobin A2 (Hb A2) (2 alpha and 2 delta globin chains) also comprises a small amount (<3.3%) of hemoglobin normally found in adults. Hb A2 values at birth are <1%.
Assisting in the diagnosis of beta-thalassemia
Quantitating the percent of hemoglobin F (Hb F) present
Assisting in the diagnosis of disorders with elevated levels of Hb F
Hemoglobin A2 (Hb A2) values of 3.5% to 9% are found in beta-thalassemia trait.
In beta-thalassemia major, hemoglobin F (Hb F) may be 30% to 90% or even more of the total hemoglobin.
Hb F concentration is usually between 5% to 15% of the total hemoglobin in delta/beta-type thalassemia trait (F-thalassemia).
Higher concentrations of Hg F occur in hemoglobin S (Hb 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 / 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 Hb A in a patient who has mostly Hgb S and a moderate increase in Hb F is strong evidence of Hgb S/beta thalassemia (if the patient has not had a transfusion).
Hb 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 (Hb F) is elevated in newborns, reaching adult levels by 12 months.
Hb 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.
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.
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%
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%
Clinical References 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