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Epic Code LAB692 Alpha-Fetoprotein, Amniotic Fluid

Additional Codes

Mayo Code: AFPA

Interface Order Alias: 10080

Epic: LAB692

CDM: 3421581

Cerner code: 1066

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful 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

Specimen Type

Amniotic Fld


Necessary 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.

Day(s) Performed

Monday through Friday

Reference Values

< 2.0 multiples of median (MoM)

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.

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.

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.

Reporting Name

Alpha Fetoprotein, AF

Method Name

AFPA: Immunoenzymatic Assay
ACHE_: Polyacrylamide Electrophoresis

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)

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

Report Available

2 to 19 days

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

Clinical Reference

1. Clinical Laboratory Standards Institute (CLSI): Maternal Serum Screening: Approved Standard. 2nd ed. I/LA25-A2 CLSI; 2011

2. Cuckle H. Prenatal screening using maternal markers. J Clin Med. 2014;3(2):504-520. doi:10.3390/jcm3020504

3. Bernard JP, Cuckle HS, Bernard MA, Brochet C, Salomon LJ, Ville Y. Combined screening for open spina bifida at 11-13 weeks using fetal biparietal diameter and maternal serum markers. Am J Obstet Gynecol. 2013;209(3):223.e1-5

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
ACHE_ Acetylcholinesterase, AF Yes No
Laboratory Test Directory | West Additional Information:

Mandatory Reflex Testing:

  • AFP >2.0 MOM, Acetylcholinestrase (sent to Mayo) will be performed.

Interface Order Information

Order Alias: 10080

Result Alias Result Name
21491 AFP Amniotic Collection Date
21492 AFP Amniotic EDD by US Scan
22984 AFP Amniotic Last Menstrual period
22985 AFP Amniotic EDD by LMP
22986 AFP Amniotic GA at Collection by Scan
22987 AFP Amniotic GA at Collection by Dated
22988 AFP Amniotic GA used
22989 Alpha Fetoprotein, AF
22990 AFP Amniotic Results
22991 AFP Amniotic Interpretation
22992 AFP Amniotic Additional Comments
22993 AFP Amniotic Follow Up
22994 AFP Amniotic General Test Info