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Test ID: ACHE_ Acetylcholinesterase, Amniotic Fluid

Reporting Name

Acetylcholinesterase, AF

Useful For

Diagnosing open neural tube defects and, to a lesser degree, ventral wall defects

Specimen Type

Amniotic Fld

Additional Testing Requirements

If chromosome studies are also requested, see CHRAF / Chromosome Analysis, Amniotic Fluid for specimen requirements. When requested with chromosome analysis, the specimen cannot be frozen.

Necessary Information

Gestational age at amniocentesis is required.

Second Trimester Maternal Screening Alpha-Fetoprotein (AFP)/QUAD Screen Patient Information (T595) is required.

Specimen Required

Container/Tube: Amniotic fluid container

Specimen Volume: 1 mL

Collection Instructions: A specimen from the 14- to 18-week gestational period of pregnancy is preferred. Amniotic fluid from the 14- to 21-week gestational period is acceptable.

Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Amniotic Fld Refrigerated (preferred) 365 days
  Frozen  365 days
  Ambient  14 days

Reference Values

Negative (reported as negative [normal] or positive [abnormal] for inhibitable acetylcholinesterase)


Reference values were established in conjunction with alpha-fetoprotein testing and include only amniotic fluids from pregnancies between 14 and 21 weeks gestation.

Day(s) Performed

Tuesday, Thursday

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
ACHE_ Acetylcholinesterase, AF 30106-9


Result ID Test Result Name Result LOINC Value
9287 Acetylcholinesterase, AF 30106-9
GACHE Gestational Age (ACHE) 18185-9

Clinical Information

Neural tube defects (NTD) are a type of birth defect involving openings along the brain and spine. They develop in the early embryonic period when the neural tube fails to close completely. NTD can vary widely in severity. Anencephaly represents the most severe type of NTD, which occurs when the cranial end fails to develop properly, resulting in an absence of the forebrain, the area of the skull that covers the brain, and the skin. Most infants with anencephaly are stillborn or die shortly after birth. NTD along the spine are referred to as spina bifida. Individuals with spina bifida may experience hydrocephalus, urinary and bowel dysfunction, club foot, lower body weakness, and loss of feeling or paralysis. Severity varies depending upon whether the NTD is covered by skin, whether herniation of the meninges and spinal cord are present, and the location of the lesion. NTD not covered by skin are referred to as open NTD and are typically more severe than closed NTD. Likewise, those presenting with herniation and higher on the spinal column are typically more severe.


Most NTD occur as isolated birth defects with an incidence of approximately 1 to 2 in 1000 live births in the United States. Rates vary by geographic region with lower rates being observed in the North and West than the South and East. A fetus is at higher risk when the pregnancy is complicated by maternal diabetes, exposed to certain anticonvulsants, or there is a family history of NTD. Studies have shown a dramatic decrease in risk as a result of maternal dietary supplementation with folic acid. The March of Dimes currently recommends that all women of childbearing age take 400 mcg of folic acid daily, increasing the amount to 600 mcg/day during pregnancy. For women who have had a prior pregnancy affected by an NTD, the recommended dose is at least 4000 mcg/day starting at least 1-month preconception and continuing through the first trimester.


When an NTD is suspected based upon maternal serum alpha-fetoprotein (AFP) screening results or diagnosed via ultrasound, analysis of AFP and acetylcholinesterase (AChE) in amniotic fluid are useful diagnostic tools. AChE is primarily active in the central nervous system with small amounts of enzyme found in erythrocytes, skeletal muscle, and fetal serum. Normal amniotic fluid does not contain AChE, unless contributed by the fetus as a result of an open NTD.


The presence of acetylcholinesterase in amniotic fluid is consistent with open neural tube defects and, to a lesser degree, ventral wall defects.

Clinical Reference

1. Wilson RD, Audibert F, Brock JA, et al: Prenatal screening, diagnosis, and pregnancy management of fetal neural tube defects. J Obstet Gynaecol Can 2014 Oct;36(10):927-939

2. Palomaki GE, Bupp C, Gregg AR, et al: Laboratory screening and diagnosis of open neural tube defects, 2019 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Genet Med 2020 Mar;22(3):462-474

Report Available

5 to 8 days

Method Name

Polyacrylamide Electrophoresis


1. Second Trimester Maternal Screening Alpha-Fetoprotein (AFP)/QUAD Screen Patient Information (T595) is required; see Special Instructions.

2. Biochemical Genetics Patient Information (T602) in Special Instructions.

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: