Home
HelpTest Code ACHE_ Acetylcholinesterase, Amniotic Fluid
Reporting Name
Acetylcholinesterase, AFUseful For
Diagnosing open neural tube defects and, to a lesser degree, ventral wall defects
Method Name
Polyacrylamide Electrophoresis
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Amniotic FldAdditional 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
1. Gestational age at amniocentesis is required.
2. If not ordering electronically, provide gestational age on Second Trimester Maternal Screening Alpha-Fetoprotein / Quad Screen Patient Information (T595) and send with specimen.
Specimen Required
Container/Tube: Amniotic fluid container
Specimen Volume: 1 mL
Collection Instructions: Specimen must be collected between 14 to 21 weeks gestation; 14 to 18 weeks is preferred.
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 |
Reject Due To
| Gross hemolysis | OK |
| Gross icterus | OK |
Special Instructions
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
CPT Code Information
82013
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 in 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 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 red blood cells, skeletal muscle, and fetal serum. Normal amniotic fluid does not contain AChE, unless contributed by the fetus as a result of an open NTD.
Interpretation
The presence of acetylcholinesterase in amniotic fluid is consistent with open neural tube defects and, to a lesser degree, ventral wall defects.
Cautions
False-positive acetylcholinesterase results may occur when blood is present in the amniotic fluid specimen or due to contamination from fetal calf serum.
Method Description
Acetylcholinesterase (AChE) and pseudocholinesterase (PChE) catalyze the deesterification of acetylthiocholine iodide to form a white copper thiocholine precipitate. The white precipitate is acted upon by dithiooxamide to provide a dark-green color. If 1,5 bis (4-allyldimethylammoniumphenyl) pentane-3-1 dibromide is present, it will inhibit the action of AChE on acetylthiocholine iodide but will not inhibit the activity of PChE. AChE and PChE are separated by polyacrylamide gel electrophoresis and then reacted with the inhibitor and substrate while remaining in the gel.(Barlow RD, Cuckle HS, Wald NJ. A simple method for amniotic fluid gel-acetylcholinesterase determination, suitable for routine use in the antenatal diagnosis of open neural tube defects. Clin Chim Acta. 1982;119:137-142); Cowan T, Pasquali M. Laboratory Investigations of Inborn Errors of Metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw Hill; 2017:1139-1158)