Fetal hemoglobin (Hb), or Hb F, is a normal Hb produced in the red blood cells of a fetus and in smaller amounts in infants. It constitutes 50% to 90% of the Hb in a newborn; the remaining Hb consists of Hb AI and Hb Az, the Hb in adults.
Under normal conditions, the body ceases to manufacture fetal Hb during the first years of life, and from that point on manufactures adult Hb. If this changeover doesn't occur and fetal Hb continues to constitute more than 5% of the Hb after age 6 months, an abnormality should be suspected, particularly thalassemia.
Procedure and posttest care
Normal values for fetal Hb range as follows:
In beta-thalassemia major, fetal Hb may be 30% or more of the total Hb. Slight increases in fetal Hb concentration appear in a variety of unrelated hematologic disorders, such as aplastic anemia, homozygous sickle cell disease, and myeloproliferative disorders. Fetal Hb commonly increases to as much as 5% during normal pregnancy.
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