2T Maternal Serum Alpha Fetoprotein (AFP) Build info

Synonyms

• 2T MATERNAL SERUM AFP
• MSAFP
• LAB14033

Procedure Name

2T MATERNAL SERUM AFP

Procedure Master Number

LAB14033

Cerner Name

2T Maternal Serum AFP

Procedure ID

182869

Clinical Info

Maternal serum AFP is a screening test for Open Neural Tube Defects (ONTD’S) such as
Open Spina Bifida (OSB) and Anencephaly. 
The test may also detect approximately 60% of Ventral Wall Defects
(VWD). A positive result means that further diagnostic testing may be offered
to the pregnant woman to determine if a structural defect is present.
MS-AFP is a screening test. 

Specimen Sources

Specimen Types

Container

Gold Top Tube

Collection Instructions

Container/Tube Gold Top Tube( prefered)  or Red Top Tube
Collection Instructions
Specimen Rejection Criteria:  Incorrect tube type,  Insufficient volume,
                                               Fetal/maternal blood contamination
                                                Out of gestational age range
Special Instructions:
The following Ask on Order Entry (AOE) patient information must be provided:
 1: Maternal Weight
 2: Race/Ethnicity
 3: Estimated Date of Delivery (EDD)
 4: Gestational Age Method
 5: Current Smoker
 6: Multiple Pregnancy Status
 7: Insulin Dependent Diabetes
 8: Family History of ONTD
 9: Valproic Acid
10: Carbamazepine 
Complete information is necessary to interpret the test. Patient information may be
provided to the laboratory using the Maternal Prenatal Screening request form
(0900).
  Specimens must be collected before amniocentesis.
 
Maternal serum AFP screening is offered for gestational ages 15.0 to 21.9 weeks.
The optimal gestational age for maternal serum AFP is 16.0 to 18.9 weeks.  

Specimen Volume

3 mL serum ( 0.5 mL min)

Transport Instructions

Room Temperature
Refrigerated for overnight delivery.

Specimen Stability

6 Days Room Temperature
14 Days Refrigerated

Methodology

Time-Resolve Amplified Cryptate Emission (TRACE)
This test was developed, and its performance
characteristics determined by Northwell Health Laboratories. It has not been
cleared or approved by the Food and Drug Administration. The methods and
performance characteristics have been reviewed and approved by the New York
State Department of Health.

Days Performed

Monday - Friday   TAT: 1-2 Days upon receipt

Performing Laboratory

Northwell Core Lab at CFAM

CPT

82105

PDM

Only Orderable at Locations:

Results

Result Interpretation

The MS-AFP level is converted into a multiple of the GA specific median (MoM) and is then adjusted based on the patient's race, weight, diabetic status, and smoking status. The ONTD cut-off is 2.5 MoM but is adjusted to account for the patient’s prior risk factors such as African America/Caribbean race, IDDM, twin pregnancy, family history and use of valproic acid or Carbamazepine. The interpretation is based on the patient's analyte adjusted AFP MoM result compared to the risk adjusted cut-off.

    Interpretation:

If the patient's MoM is less than the cut-off the test is considered "Within Normal Range". If the patient’s MoM is greater than or equal to the cut-off the test is considered "Increased Risk". Patients at increased risk are offered detailed ultrasound and diagnostic amniocentesis.

 A screen negative result indicates low risk for ONTD’s but does not guarantee the absence of neural tube defects (NTD). A screen-positive result indicates an increased risk for ONTD’s. The actual risk depends on the level of AFP and the individual's pretest risk of having a child with NTD based on family history, diabetic status, race, and use of certain seizure medications.

An interpretive risk report including the patients AFP MoM, MoM cut-off and risk for open spina bifida will be provided.

 A screen-positive result does not infer a definitive diagnosis of an ONTD but indicates that further evaluation should be considered.

Approximately 80% of pregnancies affected with an ONTD have elevated AFP MoM values greater than 2.50.

Regardless of risk results, extreme analyte results (AFP MoM > 2.5 or < 0.25), will be flagged and valuable comments and references will be provided regarding the risk of other potential adverse pregnancy outcomes such as preterm birth (<37 weeks), spontaneous abortion, fetal loss < 24 weeks, fetal loss > 24 weeks, low birth weight, placenta accreta and preeclampsia.

  Follow up: Upon receiving maternal serum screening results, all information used in the risk calculation should be reviewed for accuracy  (ie, weight, diabetic status, gestational dating). If any information is incorrect, the laboratory should be contacted for recalculation of the estimated risks. Screen-negative results typically do not warrant further evaluation. Ultrasound is recommended to confirm dates for NTD screen-positive results. If ultrasound yields new dates that differ by at least 7 days, a recalculation should be considered. The screen results are dependent on accurate information for gestation, race, IDD, and weight. Inaccurate information can lead to significant alterations in the estimated risk. In particular, erroneous assessment of gestational age can result in false-positive or false-negative screen results. Because of its increased accuracy, the determination of gestational age by ultrasound is recommended, when possible, rather than by last menstrual period.

 A screen-negative result does not guarantee the absence of fetal defects.

A screen-positive result does not provide a diagnosis but indicates that further diagnostic testing should be considered such as high-resolution  ultrasound and amniocentesis (including amniotic fluid AFP and acetylcholinesterase measurements for NTD.

 Cautions: Valid measurements of AFP in maternal serum cannot be made after amniocentesis. Triplet and higher multiple pregnancies cannot be interpreted. 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.

 Each center offering maternal serum screening to patients should establish a standard screening protocol, which provides pre- and post-screening education and appropriate follow-up for screen-positive results.

    Clinical References

1.         Maternal serum-alpha-fetoprotein measurement in antenatal screening for anencephaly and spina bifida in early  pregnancy: Report of U.K. Collaborative study on Alpha-fetoprotein in Relation to Neural-tube defects.  Lancet, 1977 Jun 25; 309(8026):1323-1332.
2.        Estimating an individual's risk of having a fetus with open spina bifida and the value of repeat alpha-fetoprotein testing. Fourth report of the UK collaborative study on alpha-fetoprotein in relation to neural tube defects. J Epidemiol Community Health. 1982 Jun;36(2):87-95. doi: 10.1136/jech.36.2.87.

3.         Stability of first- and second-trimester serum markers after storage and shipment. Lambert-Messerlian GM, Eklund EE, Malone FD, Palomaki GE, Canick JA, and  D’Alton ME. Prenat Diagn 2006; 26: 17–21.

4.         Bradley LA, Palomaki GE, McDowell GA. Technical standards and guidelines: prenatal screening for open neural tube defects. ONTD Working Group, ACMG Laboratory Quality Assurance Committee. Genet Med 2005;7:355–69.

5.         Palomaki GE,Bupp C, Gregg AR, Norton ME, Oglesbee D, Best RG.  Laboratory screening and diagnosis of open neural tube defects, 2019 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Gen Med 2020 Mar. 22(3) 462-474.

6.         ACOG Practice Bulletin No. 187 - Neural Tube Defects. Obstet Gynecol 2017 Dec. 130(6) 279-290

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