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Introduction ⬇

Hb F is a normal Hb manufactured in the RBCs of the fetus and infant; it makes up 50%–90% of the Hb in the newborn. The remaining portion of the Hb in the newborn is made up of HbA1 and HbA2, the adult types.

Under normal conditions, the manufacture of Hb F is replaced by the manufacture of adult Hb types during the first year of life. But if Hb F persists and constitutes more than 5% of the Hb after 6 months of age, an abnormality should be expected.

Determination of Hb F is used to evaluate thalassemia (an inherited abnormality in the manufacture of Hb), hemolytic anemias, hereditary persistence of fetal Hb, and other hemoglobinopathies.

Normal Findings ⬆ ⬇

Adults: 0%–2% or 0–0.02 mass fraction Hb F

Newborns: 60%–90% or 0.60–0.90 mass fraction Hb F

By 6 months of age: 2% or 0.02 mass fraction Hb F

Procedure ⬆ ⬇

  1. Use a 5-mL venous blood EDTA-anticoagulated sample for Hb electrophoresis.

  2. A blood smear stain may also be done to identify cells containing Hb F (Kleihauer–Betke stain).

Clinical Implications ⬆ ⬇

Increased Hb F is found in:

  1. Thalassemias (major and minor)

  2. Hereditary familial fetal hemoglobinemia (persistence of Hb F)

  3. Hyperthyroidism

  4. Sickle cell disease

  5. Hb H disease

  6. Anemia, as a compensatory mechanism (pernicious anemia, PNH, sideroblastic anemia)

  7. Leakage of fetal blood into the maternal bloodstream

  8. Aplastic anemia (acquired)

  9. Juvenile myeloid leukemia with absence of Philadelphia chromosome

  10. Myeloproliferative disorders, multiple myeloma, lymphoma

Clinical Alert

In thalassemia minor, continued production of Hb F may occur on a minor scale (5%–10% or 0.05–0.10), and the patient usually lives. In thalassemia major, the values may reach 40%–90% or 0.40–0.90. This continued production of Hb F leads to severe anemia, and death usually ensues

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

  2. Ensure that the test is done before transfusion.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for thalassemia and anemia.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. If analysis of the specimen is delayed for more than 2–3 hours, the level of Hb F may be falsely increased.

  2. Infants small for gestational age or with chronic intrauterine anoxia have persistently elevated Hb F.

  3. Hb F is increased during anticonvulsant drug therapy.