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Home :: Fetal hemoglobin

Fetal Hemoglobin

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.


  • To diagnose thalassemia

Patient preparation

  • Explain to the patient that this test is used to detect thalassemia disease.
  • Tell him that a blood sample will be taken, Explain who will perform the venipuncture and when.
  • Reassure him that drawing the sample will take less than 3 minutes.
  • Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
  • If the patient is a child, explain to his parents that a small amount of blood will be taken from the finger or earlobe.
  • Inform the patient or his parents that food or fluids need not be restricted before the test.

Procedure and posttest care

  • Perform a venipuncture and collect the sample of blood in a 15-ml lavender­top tube.
  • For a young child, collect capillary blood in a micro collection device.
  • If a hematoma develops at the venipuncture site, apply warm soaks.
  • Completely fill the collection tube, and invert it gently several times to mix the sample and the anticoagulant thoroughly.
  • To avoid hemolysis, don't shake the tube vigorously.

Reference values

Normal values for fetal Hb range as follows:

  • ages 0 to 30 days: 60% to 90%
  • ages 1 to 23 months: 2%
  • age 24 months to adult: 0% to 2%.
Abnormal findings

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.

Interfering factors

  • Hemolysis due to rough handling of the sample
  • Delay in analyzing the specimen for more than 2 to 3 hours (possible false­high)

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