Patient's gestational age must be at least 12 weeks for interpretation of α-fetoprotein. State gestational age by ultrasound and/or last menstrual period (LMP) on the request form. Note that AChE false-positive and false-negative results are more frequent at gestational ages of less than 13 weeks. Optimal gestational age for detection of AChE is 14 to 18 weeks.
Expected Turnaround Time
2 mL (discard first 2 mL)
Small AFP tube
Avoid contamination of amniotic fluid with maternal or fetal blood. As little as one drop of fetal blood can cause false-positive results during assay of amniotic fluid. Amniotic fluid should be collected by the attending physician.
Causes for Rejection
Specimen found not to be amniotic fluid; gross contamination of amniotic fluid with maternal or fetal blood; quantity not sufficient for analysis
Diagnose fetal open neural tube defects and some ventral wall defects.
Immunochemiluminometric assay (ICMA); acrylamide gel electrophoresis; isoelectric focusing
Note: AChE will be reflexively performed and billed when amniotic fluid α-fetoprotein (AFAFP) is elevated and/or gestational age is out of range of normative values.