Hemoglobin A2 and F, Blood
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
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%.
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%
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.
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