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Test ID AFPA Alpha-Fetoprotein, Amniotic Fluid

Reporting Name

Alpha Fetoprotein, AF

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 (AFP) is positive, then acetylcholinesterase (AChE) will be performed at an additional charge.

Specimen Type

Amniotic Fld


Specimen Required


Container/Tube: Amniotic fluid container

Specimen Volume: 1 mL

Collection Instructions: Do not centrifuge.

Additional Information:   

1. The following information is required:

a. Date ultrasound performed

b. Estimated due date by ultrasound

c. Collection date

d. Gestational age must be between 13 and 24 weeks; 16 to 18 weeks preferred.

2. If chromosome studies are also requested, see AF / Chromosome Analysis, Amniotic Fluid. The specimen for AFP-AF testing, when requested with chromosome analysis, cannot be frozen.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Amniotic Fld Refrigerated 7 days

Reference Values

≤2.0 multiples of median (MoM)

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-5 p.m., Saturday; 6 a.m.-1 p.m.

Test Classification

This test has been cleared or approved by the U.S. 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.

CPT Code Information

82106-AFP

82013-Acetylcholinesterase (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 29595-6
24241 Results 43798-8
24235 Interpretation 59462-2
24236 Additional Comments 55107-7
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 daltons. 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 nonpregnancy 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 renal 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 diagnostic 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.

Clinical Reference

Assessing the Quality of Systems for Alpha-Fetoprotein (AFP) Assays Used in Prenatal Screening and Diagnosis of Open Neural Tube Defects: Approved Guideline. NCCLS I/LA17-A Vol 17. No 5. April 1997

Analytic Time

2 days

Method Name

AFPA: Immunoenzymatic Assay
ACHE_: Polyacrylamide Electrophoresis