Sign in →

Epic Test Code LAB663 Alpha-Fetoprotein, Amniotic Fluid

Additional Codes

MML Code: AFPA

 

NY State Approved

Yes

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Reporting Name

Alpha Fetoprotein, AF

Method Name

AFPA: Immunoenzymatic Assay

ACHE_: Polyacrylamide Electrophoresis

Specimen Stability Information

Specimen Type Temperature Time Special Container
Amniotic Fld Refrigerated (preferred) 7 days
  Ambient  7 days


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


Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Container/Tube: Plain, plastic, screw-top tube

Specimen Volume: 0.75 mL

Collection Instructions: Do not centrifuge.


Specimen Type

Amniotic Fld

Specimen Minimum Volume

0.5 mL

Reference Values

< 2.0 multiples of median (MoM)

Report Available

2 to 19 days

Day(s) Performed

Monday through Friday

CPT Code Information

82106

82013 (if appropriate)

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

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

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.

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.

 

Acetylcholinesterase 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.

Specimen Retention Time

2 weeks