What Is The Serum Integrated Screen?
The Serum Integrated Test helps determine the risk of having a pregnancy affected by Down syndrome and Open Neural Tube Defects (ONTD). The test is performed in two stages. The first stage can be performed between 11 weeks and 13 weeks and 6 days. The second stage can be performed between 15 and 22 weeks.
In the first stage, an ultrasound scan is used to precisely determine the gestational age of the pregnancy (to ensure that testing is being performed at the proper time.) A blood sample is taken to measure the level of pregnancy-associated plasma protein-A (PAPP-A).
In the second stage, a second blood sample is taken to measure levels of four markers:
- Alpha-fetoprotein (AFP)
- Total beta-human chorionic gonadotropin (total ß-hCG)
- Unconjugated Estriol (uE3)
In pregnancies affected by Down syndrome, the levels of PAPP-A, AFP, and uE3 tend to be lower than normal while the levels of inhibin and total ß-hCG are elevated.
In a pregnancy affected by ONTDs such as open spina bifida or anencephaly, the level of AFP tends to be elevated.
What Is The Difference Between the Integrated Test and Serum Integrated Test?
- The Serum Integrated Test includes the same serum markers as the Integrated Test, but it does not use a Nuchal Translucency (NT) ultrasound measurement. The Serum Integrated Test is useful when NT ultrasound is not available, and it is more accurate than the AFP+Quad Test (a detection rate of 86% vs. 79%.)
What Does A Screen Negative Test Result Mean?
- If the risk of Down syndrome based on age and the level of the markers is lower than 1 in 270, then the result is considered screen negative and a diagnostic test such as amniocentesis would not usually be offered.Although a screen negative test result means that the patient is not at high risk for having a baby with Down syndrome, a screen negative result does not completely rule out the possibility of a pregnancy with Down syndrome
What Does A Screen Positive Result Mean?
- A screen positive result for the Serum Integrated means there is a risk of greater than or equal to 1 in 270 of a Down syndrome pregnancy. About 5% of patients who have the Serum Integrated receive a screen positive result.
Why Wait Until The Second Stage To Have A Risk Estimate?
- Using information from the first and second trimester yields a higher detection rate than a test using information from the first stage alone. Additionally, a test using only information from the first trimester cannot assess risk for ONTDs.