Sequential 1

Alphabetical Test listing

Sequential 1-13500

Sequential 1
Down Syndrome
Nuchal Translucency (NT)

Screening test for Open Spina Bifida/ONTD, Trisomy 21/Down syndrome, and Trisomy 18/Edwards syndrome.

3.0 mL
1.0 mL
  • Collect between 10.0 and 13.9 weeks of gestation.
    • NT can be assessed when the CRL is 45 - 84 mm

  • Maternal serum specimens must be drawn prior to amniocentesis to avoid contamination with fetal blood.



  1. Allow blood to clot
  2. Separate serum from cells by centrifugation - pour off is not advised



Gold serum separator (SST) tube


Ambient (preferred) - 7 days

Refrigerated - 14 days

Frozen - 14 days

  • Gross hemolysis
  • Gross lipemia
  • Quantity not sufficient for analysis (QNS)
  • Improper specimen type
LabCorp RTP (017700): R-LC
Mo - Sa
2 - 5 days

Chemiluminescent immunoassay immunoassay (EIA)


An interpretive report will be provided


Sequential screening provides a first trimester risk assessment.

Following the Sequential 1 blood draw, the PAPPA-A, hCG, NT, and other provided demographics are used to give a risk for Down syndrome and trisomy 18. If the risk is greater than 1 in 45 for Down syndrome or 1 in 100 for T18, then it is considered screen positive and it is recommended to offer diagnostic testing. If the risks are less than those cut offs then it is recommended to draw for the Sequential 2.

After the 2nd draw, a new risk is calculated for Down syndrome, trisomy 18 and open spina bifida using data from the first and second draws.

Result 77202-0