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Integrated Screen, Full or Serum

First Trimester - PAPP-A (SINTI), Second Trimester - AFP, hCG, uE₃, Inhibin A (SINT2)

Test Codes

First Trimester Serum: EPIC: LAB5778, SOFT: SINTI, Second Trimester/Final Serum: EPIC: LAB5779, SOFT: SINT2, First Trimester Full: EPIC: LAB5780, SOFT: INT1, Second Trimester/Final Full: EPIC: LAB5781, SOFT: INT2

Department

Special Chemistry

Instructions

• The full integrated screen requires nuchal translucency (NT) measured by an ultrasonographer approved by Clinical Pathology. 
• A completed prenatal screening requisition form must accompany all samples to obtain risk interpretation.

Specimen Collection Criteria

Collect: This test requires:

• One Gold-top SST tube at 11-13 weeks gestational age. (Minimum Whole Blood: 4.0 mL) 
• One Gold-top SST tube at 15-22 weeks gestational age. (Minimum Whole Blood: 4.0 mL)

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged collection tube within two hours of collection. Specimens for uE₃ (15-22 weeks gestational age) should not be frozen as this may have a detrimental effect on the assay. (Minimum Serum: 1.0 mL)

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2-8°C or 36-46°F). (Minimum Serum: 1.0 mL)

Rejection Criteria

• Plasma specimens. 
• Severely hemolyzed, lipemic or icteric specimens.  
• Specimens not collected and processed as indicated. 

 

In-Lab Processing

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Room temperature is acceptable for a maximum of two hours. Specimens for uE₃ (15-22 weeks gestational age) should not be frozen as this may have a detrimental effect on the assay. (Minimum Serum: 1.0 mL)

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 24 hours
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Special Testing Laboratory.

Performed

First Trimester Testing (PAPP-A) performed Monday - Friday.
Final results are not available until the 2^nd trimester sample has been tested.

Second Trimester Testing (AFP, hCG, uE₃, Inhibin A) performed Monday - Friday.
Results available the next business day.

Reference Range

The screen includes quantitation of PAPP-A (pregnancy-associated plasma protein A) in the 1^st trimester and AFP, hCG, unconjugated estriol (uE₃), and inhibin A in the second trimester. The result of each test is reported as an MoM (multiple of the median) that is adjusted for the weight, race when appropriate and gestational age. An adjustment for insulin-dependent diabetes is made when appropriate. The risk cut off for Down's syndrome is 1:270. The risk of an open neural tube defect is determined by comparing to the absolute cut-off for AFP of 2.2 MoM.

Test Methodology

Chemiluminescence Immunoassay.

Interpretation

Down's Syndrome
In comparison to a normal pregnancy, Down's syndrome results in lower PAPP-A, AFP and uE₃ results and higher hCG and Inhibin A results. The risk of Down's syndrome is calculated based on serum markers, and the age of the pregnant woman. If a nuchal translucency (NT) measurement has been performed, an NT MoM will be calculated and the information incorporated with the lab tests to give a final Down's syndrome risk. The NT in Down's syndrome is greater than in an unaffected fetus. Because the calculated MoM for each test takes into account the patient's gestational age, it is essential that gestational age information is based on ultrasound. Because this is a screen for Down's syndrome, a number of positive results will be determined to be false positives. However, use of the Full Integrated screen should yield a lower number of false positives than the Quad screen.

Trisomy 18
A Trisomy 18 fetus results in decreased levels of AFP, hCG and uE₃ compared to a normal pregnancy. Levels of these three biochemical markers together with patient age are used to calculate a risk of Trisomy 18. This is considered increased when the risk is greater than 1:100. Only increased Trisomy 18 risks will be reported.

Smith Lemli Opitz syndrome (SLOS)
A fetus with SLOS results in a decreased level of uE₃. The risk is considered to be increased when the risk is greater than 1:50.

Donated Eggs
If a pregnancy has resulted from use of a donated ovum, the age of the egg donor is used to calculate Down syndrome and Trisomy 18 risk assessments. It is therefore essential that the egg donor's date of birth or age is given to the lab with other patient information.

Women Aged 35 Years and Older
Because this screen cannot detect all chromosomal abnormalities, the college of American Obstetrics and Gynecologists still recommends amniocentesis and cytogenetics in women of this age.

Open Neural Tube Defect (ONTD)
ONTD risk assessment is also reported as part of the Full or Serum Integrated screen. A fetus with an open neural tube defect (open spina bifida or anencephaly) frequently results in an increased level of AFP in maternal blood. Other conditions may also result in increased AFP levels (e.g., undiagnosed multiple gestation, fetal ventral wall defects, congenital nephrosis, fetal distress or death or maternal liver disease).

Clinical Utility

The Integrated screen is a screen used to determine the risk of a woman having a Down's syndrome fetus. It is not a diagnostic test. The AFP level alone is used to calculate the risk of the fetus having an open neural tube defect (ONTD). Although screening for ONTD can be performed between 15 and 22 weeks gestational age, the optimal time is between 16 and 18 weeks gestational age. Screening for Down's syndrome can only be performed between 14 and 22 weeks. The risk of Trisomy 18 is also calculated from patient age and test results; the risk is reported as increased if it is greater than 1:100.

Reference

1. Malane, F.D. et al. First-Trimester or Second-Trimester Screening, or both, for Down's syndrome. New England J. Med (2005). 353: 2001-2011.

CPT Codes

LOINC:  PAPP-A 48407-1

Contacts

Last Updated

1/11/2023