II. Indications
- Pregnancy screening for congenital defect
- See Triple Screen
-
Tumor Marker
- Cirrhosis with liver mass (Hepatocellular Carcinoma)
- Nonseminomatous germ cell tumor monitoring
- AFP used in combination with bHCG
III. Background
- Fetal Glycoprotein with molecular weight of 70,000
- Sites of synthesis
- Embryonic Yolk Sac
- Developing Gastrointestinal Tract
- Liver
- AFP is major Protein in developing fetus
- Decreases to undetectable level after birth
IV. Interpretation
- Non-pregnant
- Normal AFP <5.4 ng/ml (5.4 ug/L)
- AFP >500 ng/ml unlikely to be from benign cause
- Nonseminomatous germ cell tumor
- Poor prognosis if AFP > 10,000 ng/ml at diagnosis
- AFP >10,000 associated with 50% five year survival
- Normal pregnancy
- See Triple Screen for interpretation
- Fetal serum AFP: Peaks at 3 mg/ml at 13 weeks
- Amniotic fluid AFP: Peaks at 30 ug/ml at 13 weeks
- Maternal Serum AFP: Peaks at 100 ng/ml at 30 weeks
V. Causes: Increased AFP in Non-Pregnant States
- Benign causes of increased AFP
- Cirrhosis
- Acute or chronic active Viral Hepatitis
- Pregnancy (see below)
- Malignant causes of increased AFP
- Hepatocellular Carcinoma (usually AFP >1000 ng/ml)
- Testicular Cancer (non-seminomatous germ cell tumor)
- Gastric Cancer
- Biliary cancer
- Pancreatic Cancer
VI. Causes: Abnormal Maternal Serum AFP (MSAFP) in Pregnancy
- Accurate Pregnancy Dating is critical
- AFP interpreted per Gestational age
- Incorrect dates is most common cause for abnormal AFP
- AFP increases by Gestational age in normal pregnancy
- Increased: Fetal malformation
- Neural Tube Defect
- Sacrococcygeal Teratoma
- Exomphalos
- Gastroschisis
- Cystic Hygroma
- Placental abnormalities
- Renal abnormalities
- Osteogenesis imperfecta
- Threatened Abortion or Fetal death in utero
- Decreased maternal weight or IUGR
- Multiple Pregnancy (Twin Gestation)
- Decreased
- Incorrect Gestational age (older than calculated)
- Trisomy 21 (Down Syndrome)
- Trisomy 18 (Edward's Syndrome)
- Hydatiform mole
- Fetal demise
- Increased maternal weight
VII. Efficacy: Congenital defect detection in pregnancies
- Multiple of median (MOM) cut-off over 2.0 to 2.5
- False Positive Rate in normal pregnancies: 5%
- Trisomy 21 sensitivity: 21%
- Only marker in Triple Screen for Neural Tube Defect
- Anencephaly sensitivity: 90%
- Spina bifida sensitivity: 80%
VIII. Efficacy: Hepatocellular Carcinoma
- Increased in 80% of Hepatocellular Carcinoma cases
- Over 1000 ng/ml in 40% of Hepatocellular Carcinoma
IX. Monitoring: Non-seminomatous germ cell tumor
- Initial: AFP with bHCG q1-2 months for 1 year
- Later: AFP with bHCG q3 months for 1 year