Alpha Fetoprotein

Alpha-fetoprotein (AFP) is a glycoprotein produced by fetal tissue and tumors that differentiate from midline embryonic structures. During fetal development, AFP levels in serum and amniotic fluid rise. AFP crosses the placenta and appears in maternal serum.

High maternal serum AFP levels may suggest fetal neural tube defects, such as spina bifida and anencephaly, but positive confirmation requires amniocentesis and ultrasonography. Other congenital anomalies, such as Down syndrome and other chromosomal disorders, may be associated with low maternal serum AFP concentrations.

Elevated AFP levels in patients who aren't pregnant may occur in cancers, such as hepatocellular carcinoma, or certain nonmalignant conditions, such as ataxia-telangiectasia. In these conditions, AFP assays are more useful for monitoring response to therapy than for diagnosis. AFP levels are best determined by enzyme immunoassay on amniotic fluid or serum.

Purpose

• To monitor the effectiveness of therapy in malignant conditions, such as hepatomas and germ cell tumors, and certain nonmalignant conditions, such as ataxia-telangiectasia
• To screen for the need for amniocentesis or high-resolution ultrasonography in a pregnant woman

Patient preparation

• Explain to the patient that this test monitors her response to therapy by measuring a specific blood protein. Advise her that further testing may be necessary.
• Tell her that she needn't restrict food, fluids, or medications before the test.
• Tell her that this test requires a blood sample and who will perform the venipuncture and when.
• Reassure her that although she may experience transient discomfort from the needle puncture and the tourniquet, collecting the sample takes less than 3 minutes.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml red-top tube.
• Record the patient's age, race, weight, and gestational period on the laboratory slip.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Handle the sample gently to prevent hemolysis.

Reference values

When testing by immunoassay, AFP values are less than 15 ng/ml in men and nonpregnant women. Values in maternal serum are less than 2.5 multiples of median (Mom) for fetal gestational age.

Abnormal findings

Elevated maternal serum AFP levels may suggest neural tube defects or other tube anomalies. Maternal AFP levels rise sharply in the maternal blood of about 90% of women carrying a fetus with anencephaly and in 50% of those carrying a fetus with spina bifida. Definitive diagnosis requires ultrasonography and amniocentesis. High AFP levels may indicate intrauterine death. Sometimes high levels indicate other anomalies, such as duodenal atresia, omphalocele, tetralogy of Fallot, and Turner's syndrome.

Elevated serum AFP levels occur in 70% of nonpregnant patients with hepatocellular carcinoma. Elevated levels are also related to germ cell tumor of gonadal, retroperitoneal, or mediastinal origin. Serum AFP levels rise in ataxia-telangiectasia and sometimes in cancer of the pancreas, stomach, or biliary system and in nonseminiferous testicular tumor. Transient modest elevations can occur in nonneoplastic hepatocellular disease, such as alcoholiccirrhosis and acute or chronic hepatitis. Elevation of AFP levels after remission suggests tumor recurrence.

In hepatocellular carcinoma, a gradual decrease in serum AFP levels indicates a favorable response to therapy. In germ cell tumors, serum AFP levels and serum human chorionic gonadotropin levels should be measured concurrently.

Low serum AFP values correlate with chromosomal disorders but require further investigation. Failure of the AFP value to return to normal by about 1 month after cancer therapy suggests the presence of residual tumor.

Interfering factors

• Hemolysis due to rough handling of the sample
• Multiple pregnancies (possible false­positive)