Acetylcholinesterase, Amniotic Fluid (AChE-AF), Amniotic Fluid
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Diagnosing open neural tube defects, and to a lesser degree, ventral wall defects
Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
Because false-positive acetylcholinesterase (AChE) may occur from a bloody tap, specimens with positive AChE results will also be tested for the presence of fetal hemoglobin at no additional charge.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
AChE-AF (Acetylcholinesterase, Amniotic Fluid)
Amniotic Fluid, Acetylcholinesterase
Amniotic Fluid, Acetylcholinesterase
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube: Amniotic fluid container
Specimen Volume: 1 mL
1. 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.
2. Do not centrifuge.
1. Gestational age at amniocentesis is required.
2. If chromosome studies are also requested, see AF/8426 Chromosome Analysis, Amniotic Fluid. The specimen for acetylcholinesterase testing, when requested with chromosome analysis, cannot be frozen.
1. Second Trimester Maternal Screening Alpha-Fetoprotein (AFP)/QUAD Screen Patient Information Sheet (Supply T595) is required; see Special Instructions.
2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.
3. If not ordering electronically, please submit the following forms with the specimen:
-Cytogenetics/AFP Congenital Disorders Request Form (Supply T238)
-Biochemical Genetics Request Form (Supply T439)
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Mild OK; Gross OK
Mild OK; Gross OK
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
|Amniotic Fld||Refrigerated (preferred)||365 days|
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Neural tube defects (NTDs) 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 completely close. NTDs can vary widely in severity. Anencephaly represents the most severe end of the spectrum and occurs when the cranial end fails to form, 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. NTDs 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. NTDs not covered by skin are referred to as open NTDs and are typically more severe than closed NTDs. Likewise those presenting with herniation and higher on the spinal column are typically more severe.
Most NTDs occur as isolated birth defects with an incidence of approximately 1 in 1,000 to 2 in 1,000 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 NTDs. 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 micrograms of folic acid daily, increasing the amount to 600 mg/day during pregnancy. For women who have had a prior pregnancy affected by an NTD, the recommended dose is at least 4,000 mg/day starting at least 1 month preconception and continuing through the first trimester.
When a 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.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
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.
The presence of acetylcholinesterase in amniotic fluid is positive for a neural tube defect if fetal hemoglobin contamination can be ruled out.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
False-positive acetylcholinesterase (AChE) results may occur when blood is present in the amniotic fluid specimen. For this reason, fetal hemoglobin analysis is performed on all specimens with a positive AChE result.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Muller F: Prenatal biochemical screening for neural tube defects. Childs Nerv Syst 2003 Aug;19(7-8):433-435 Epub 2003 Jul 12
2. March of Dimes: Neural tube defects. [Accessed 7/19/12] Available from URL: http://www.marchofdimes.com/baby/birthdefects_neuraltube.html
Method Description Describes how the test is performed and provides a method-specific reference
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 (BW284C51) 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)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Tuesday, Thursday; 8 a.m. (not reported on Saturday and Sunday)
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
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 U.S. Food and Drug Administration.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
|Result ID||Reporting Name||LOINC Code|
|GACHE||Gestational Age (ACHE)||18185-9|