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HelpTest Code AFPA Alpha-Fetoprotein, Amniotic Fluid
Reporting Name
Alpha Fetoprotein, AFUseful For
Screening for open neural tube defects or other fetal abnormalities
Follow-up testing for patients with elevated serum alpha-fetoprotein results or in conjunction with cytogenetic testing
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| ACHE_ | Acetylcholinesterase, AF | Yes | No |
Testing Algorithm
If alpha-fetoprotein is positive, then acetylcholinesterase will be performed at an additional charge.
Method Name
AFPA: Immunoenzymatic Assay
ACHE_: Polyacrylamide Electrophoresis
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Amniotic FldNecessary Information
The following information is required:
1. Estimated due date by ultrasound
2. Collection date
3. Gestational age must be between 13 and 24 weeks; 16 to 18 weeks preferred.
If not ordering electronically, provide information 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: 0.75 mL
Collection Instructions: Do not centrifuge.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Amniotic Fld | Refrigerated (preferred) | 7 days | |
| Ambient | 7 days |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Special Instructions
Reference Values
< 2.0 multiples of median (MoM)
Day(s) Performed
Monday through Friday
CPT Code Information
82106
82013 (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| AFPA | Alpha Fetoprotein, AF | 58735-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 6739 | Collection Date | 58734-5 |
| DAT15 | EDD by US Scan | 11781-2 |
| 6740 | Last Menstrual Period (LMP) | 8665-2 |
| 24233 | EDD by LMP | 11779-6 |
| 24239 | GA at Collection by Scan | 11888-5 |
| 24240 | GA at Collection by Dates | 11885-1 |
| 24234 | GA Used | 21299-3 |
| 9950 | Alpha Fetoprotein, AF | 1832-5 |
| 24241 | Results | 29595-6 |
| 24235 | Interpretation | 59462-2 |
| 24236 | Additional Comments | 48767-8 |
| 24237 | Follow up | 80615-8 |
| 24238 | General Test Info | 48767-8 |
Clinical Information
Alpha-fetoprotein (AFP) is a single polypeptide chain glycoprotein with a molecular weight of approximately 70,000 Da. Synthesis of AFP occurs primarily in the liver and yolk sac of the fetus. It is secreted in fetal serum, reaching a peak at approximately 13 weeks gestation, after which it rapidly declines until about 22 weeks gestation and then gradually declines until term. Transfer of AFP into maternal circulation is accomplished primarily through diffusion across the placenta. Maternal serum AFP levels rise from the normal non-pregnancy level of 0.20 ng/mL to about 250 ng/mL at 32 weeks gestation.
If the fetus has an open neural tube defect, AFP is thought to leak directly into the amniotic fluid, causing unexpectedly high concentrations of AFP. Other fetal abnormalities such as omphalocele, gastroschisis, congenital kidney disease, and esophageal atresia; and other fetal distress situations such as threatened abortion, prematurity, and fetal demise, may also show AFP elevations. Decreased amniotic fluid AFP values may be seen when gestational age has been overestimated.
Interpretation
A screening alpha-fetoprotein (AFP) cutoff level of 2.0 multiples of median (MoM), followed by acetylcholinesterase (AChE) confirmatory testing on positive results, is capable of detecting 96% of open spina bifida cases with a false-positive rate of only 0.06% in non-blood-stained specimens.
AChE analysis is an essential confirmatory test for all amniotic fluid specimens with positive AFP results. Normal amniotic fluid does not contain AChE, unless contributed by the fetus as a result of open communication between fetal central nervous system (eg, open neural tube defects) or, to a lesser degree, fetal circulation. All amniotic fluid specimens testing positive for AFP will have the AChE test performed. False-positive AChE may occur from a bloody tap, which may cause both elevated AFP and AChE levels.
Cautions
This test is for screening only.
Increases in alpha-fetoprotein (AFP) are not specific for neural tube defects, and the test must be used in combination with other procedures, such as ultrasonography and acetylcholinesterase measurements.
Elevated AFP levels also can be caused by benign factors and incorrect gestational dating.
Negative results do not guarantee the absence of defects.
In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results, and the laboratory should be alerted if the result does not correlate with the clinical presentation.
Method Description
The Access AFP (alpha-fetoprotein) assay is a 2-site immunoenzymatic sandwich assay. A sample is added to a reaction vessel with mouse monoclonal anti-AFP alkaline phosphatase conjugate and paramagnetic particles coated with a second mouse monoclonal anti-AFP antibody. The AFP in the sample binds to the immobilized monoclonal anti-AFP on the solid phase while, at the same time, the monoclonal anti-AFP-alkaline phosphatase conjugate reacts with different antigenic sites on the sample AFP. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. The chemiluminescent substrate Lumi-Phos530 is added to the reaction vessel and light generated by the reaction is measured by a luminometer. The light production is directly proportional to the amount of AFP in the sample. The amount of analyte in the sample is determined by means of a multipoint calibration curve.(Package insert: Access AFP. Beckman Coulter Inc; 04/2020)