SequentialScreen Part 1

CPT [MAAA: 81508] or 84163; 84702
  • Down Syndrome
  • Nuchal Translucency (NT)
  • PAPP-A

Test Details


Screening test for open neural tube defects, Down syndrome, and trisomy 18

Special Instructions

For test inquiries, call CMBP genetic services at 800-345-4363. Client must provide fetal nuchal translucency (NT) measurement and crown rump length measurement. The NT measurement must be performed by a sonographer credentialed by the Fetal Medicine Foundation or other equivalent entity. The sonographer's credential/certification number must be provided. The following information also must be provided: patient's race, patient's weight, patient's date of birth, patient's insulin-dependent diabetic status, and the number of fetuses. Also indicate patient history (i.e. prior Down syndrome pregnancy, ultrasound anomalies). Complete information is necessary to interpret the test. Patient information may be provided to the laboratory using the Maternal Prenatal Screening requisition 0900. Serum testing is provided from 10.0 to 14.0 weeks of gestation. NT can be assessed when the CRL is 45 to 84 mm.


Sequential screening requires two specimens: one collected in the first trimester and one in the second trimester. This test number is for the first trimester portion of the test. Result interpretation for the first trimester portion will be provided only for screen-positive specimens. Result interpretation for all others will be provided only when the second trimester specimen is received and tested. This is a screening test. A positive result means that diagnostic testing may be offered to the pregnant woman to determine if a neural tube defect or chromosome abnormality is present.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


Chemiluminescent immunoassay

Specimen Requirements

Information on collection, storage, and volume




3 mL

Minimum Volume

1 mL


Gel-barrier tube

Storage Instructions

Room temperature

Causes for Rejection

Gross hemolysis; gross lipemia; quantity not sufficient for analysis; improper specimen type


Collect in serum separator tube with gel barrier. Allow blood to clot, avoiding hemolysis. Separate serum from cells by centrifugation. Transport spun tube to testing laboratory.

Pour-off is not advised. Maternal serum specimens must be drawn prior to amniocentesis to avoid contamination with fetal blood.