Fetal Hemoglobin (Hb F) Test: Why It’s Important?

Hemoglobin found in red blood cells binds oxygen. The three types of hemoglobin present in humans are embryonic, fetal, and adult.

Importance of Fetal Hemoglobin (Hb F), Quantitative Test

The fetal hemoglobin (Hb F) test is conducted to determine the concentration of fetal hemoglobin in the blood sample.

Hemoglobin F is a type of hemoglobin that exists in fetuses and infants but is replaced by a different form of hemoglobin (Hb A) at about two years of age. However, Hb F levels may become elevated due to sickle cell anemia, beta-thalassemia, leukemia, or any hereditary blood disorder. A quantitative test for fetal hemoglobin is therefore recommended to screen for these types of blood disorders in both children and adults.

Indications for HbF Testing

A Hb F test may be necessary if there is a suspicion of diseases like beta-thalassemia, myeloid leukemia, or sickle cell disease. Where there is a family history of such conditions, it is advisable to have the Hb F test done, as they are commonly hereditary.

Most of a newborn’s hemoglobin is Hb F, but this goes down over the first few months; by 1 year, it is <2%, and by 2 years, it is <1%.

Hb F is present in a subgroup of red blood cells called 'F-cells.' The percentage of these unique cells in the RBCs of adults can range from 0.3% to 4.4%, being much higher in early infancy, and this varies widely among individuals. Elevated levels of Hb F may be due to increased F-cell numbers or increased Hb F concentration within the F cell.

Patients with beta-thalassemia major or other beta-thalassemia combinations may have up to 90% of their total Hb as Hb F.

Elevated levels of Hb F are seen in sickle cell disease, aplastic anemia, acute leukemia, and myeloproliferative disorders. It is also frequently increased in hemoglobinopathies where there is associated hemolysis. Certain medications like hydroxyurea, decitabine, and lenalidomide may be a cause of raised Hb F levels. In the course of pregnancy, Hb F can elevate up to 10%. A fetal hemoglobin test in pregnancy can aid in detecting fetal-maternal hemorrhage, which refers to the loss of fetal blood cells in the maternal blood circulation.

Symptoms of Common Blood Disorders

Symptoms of common blood disorders such as sickle cell anemia vary from person to person and may change over time. Symptoms can include:

Fatigue: Normal red blood cells live about 120 days in the bloodstream before dying, while sickle-shaped cells typically die after just 10–20 days. The resulting shortage of red blood cells is referred to as anemia. The lack of red blood cells prevents the body from receiving sufficient oxygen, resulting in fatigue.

Pain: Sickle cell anemia can cause extremely painful episodes called pain crises. Pain crises occur when the sickle-shaped red blood cells block blood flow through tiny blood vessels to your chest, abdomen, and joints.

Swelling of hands and feet: The blocked blood flow can cause swelling in the hands and feet.

Recurrent infections: The spleen is an organ that helps your body fight infections. Sickle cells can damage the spleen and make you more likely to get infections. Infants and young children with sickle cell anemia may begin routine vaccinations and take antibiotics to prevent life-threatening infections, such as pneumonia.

Growth problems or delayed puberty: Red blood cells are needed to deliver oxygen and nutrients throughout the body for growth. A shortage of red blood cells can slow growth in infants and children and delay puberty in teenagers.

Vision problems: Tiny blood vessels that supply your eyes may become plugged with sickle cells. This can damage the part of the eye that processes visual images (retina) and lead to vision problems.

Fetal Hemoglobin Test Procedure and General Information

The HbF test usually does not need any specific preparation. It is important to inform your healthcare provider about any medications you are taking, as they could impact the test results.

Fetal Hemoglobin Normal Range

Test results can vary depending on your age, gender, and health history. The lab that does the test may also affect the results. Abnormal results do not always mean you have a health problem. You will need to talk with your doctor about what your test results mean for you.

Healthy adults have very little HbF in their blood. Higher levels of HbF could mean you have a blood disorder, such as thalassemia or sickle cell anemia, or another condition that causes high HbF levels.

The Hb F test measures the amount of fetal hemoglobin in your blood. Fetal hemoglobin is one of several types of hemoglobin. A baby developing in the womb has high levels of HbF. The level of HbF usually drops to a very low level by 6 months after birth. In an adult or child, a higher than normal level of HbF may mean you have a blood disorder such as thalassemia, myeloid leukemia, or sickle cell anemia.