Test Description:
Neural tube defects such as spina bifida or anencephaly result when the embryonic neural tube fails to close properly at approximately 4 weeks gestation. Prenatal screening for an open neural tube defect (ONTD) is possible by measuring the level of alpha fetoprotein (AFP) in maternal serum. Screen positive results are defined as those with an AFP MoM of 2.2 or greater. The optimal time for screening is 16 to 18 weeks geatation, however, results can be provided on samples between 15 and 22 weeks 6 days. The detection rate is 85% with less than a 3% screen positive rate. Ultrasound dating (especially the use of biparietal diameter) increases the detection rate and lowers the screen positive rate. Obtaining a second specimen for repeat testing at least seven days after the first may be beneficial when the initial specimen has a slightly elevated AFP (below 3.5 MoM) and a gestational age early enough to allow time for appropriate follow-up (below 19 weeks gestation).
Conditions other than an ONTD associated with positive screening results include a multiple gestation, recent fetal demise or ventral wall defects such as omphalocele or gastroschisis. Unexplained elevated AFP levels are associated with an increased incidence of poor pregnancy outcome (e.g., low birth weight, pre-term delivery).
The Quadruple and Integrated Tests are screens that include MSAFP for ONTD screening. MSAFP screening alone should be offered to patients who have had a First Trimester Test or chorionic villus sampling as these do not include screening or diagnostic testing for ONTDs.
Methods:
Quantitative determination of AFP in serum by chemiluminescent immunoassay using the Beckman Coulter Access System.
Specimen Requirements:
10 ml of whole blood (5 ml minimum) or 2 ml serum drawn in a plain red top tube or a red corvac tube containing separation gel. Specimen must be drawn between 15 weeks, 0 days and 22 weeks, 6 days gestation.
Shipping Instructions:
Refrigeration and centrifugation are not required. Mail within 3 days of draw date to the MSU Prenatal Screening Program, Michigan State University, B-123 Life Sciences Building, East Lansing, MI 48824. Please call (517) 353-2032 or (877) TEST-DNA with any questions.
Turnaround Time: 1-2 days following receipt of sample
Test CPT Code: 82105
Relevant Links: