Indications for Acetylcholinesterase (AChE) Assay
Acetylcholinesterase (AChE) is a neural enzyme present in cerebral spinal fluid and fetal blood. AChE is not present in maternal blood and is not normally measurable in amniotic fluid. The abnormal presence of acetylcholinesterase in amniotic fluid is indicative of an open fetal defect. When AChE is detected, the ratio of AChE to pseudocholinesterase (PChE), a non-specific cholinesterase usually found in amniotic fluid, may help distinguish open neural tube defects from open ventral wall defects or fetal blood contaminated fluid.
Specimen Requirements
Amniotic fluid, 2-5 ml, obtained between 14 – 24 weeks gestation. Results for specimens obtained prior to 14 weeks or after 24 are less reliable.
All specimens must be labeled with the patient’s name, Date of birth and include a completed test requisition.
Methodology
Acetylcholinesterase testing is performed on all amniotic fluid samples for which there is an increased risk of a neural tube defect or other fetal abnormalities. Increased risk is defined by abnormal AF-AFP results or abnormal ultrasound findings.
Amniotic fluid is examined for the presence of acetylcholinesterase and pseudocholinesterase by using slab gel electrophoresis. When acetylcholinesterase is detected, the ratio of acetylcholinesterase to pseudocholinesterase may help distinguish an open neural tube defect from an open ventral wall defect or fetal blood contaminated fluid.
Transport Temperature
Transport amniotic fluid samples at ambient temperature by same day or overnight courier. In high temperatures, the specimen should be packed with a cold-pack and shipped at 2°-8°C.
Causes for Rejection
Amniotic fluid: Frozen specimen, excessive amounts of blood, inappropriate container
Turnaround Time
Approximately one week is required for the AChE assay