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Obstetric Quad Screen

Quad Screen

Test Codes

Antrim #31362, EPIC: LAB5777, SOFT: QUAD

Department

Special Chemistry

Specimen Collection Criteria

Collect: One Gold-top SST tube. (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

Monday – Friday.
Results available next business day once all patient results and history have been completed.

Reference Range

The screen includes quantitation of AFP, hCG, unconjugated estriol (uE₃), and inhibin A. The result of each test is reported as an MoM (multiple of the median) that is adjusted for the weight, race and is calculated for the appropriate gestational age. An adjustment for insulin-dependent diabetes is made when appropriate. The risk of Down syndrome is compared to that of a 35-year-old in the 2^nd trimester (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

Chemiluminescent Immunoassay.

Interpretation

In comparison to a normal pregnancy, Down syndrome is associated with lower AFP and uE₃ results and higher hCG and Inhibin A results. The risk of Down syndrome is calculated based on levels of AFP, hCG, uE₃ and inhibin A and the age of the pregnant woman. Because the calculated MoM for each test takes into account the patient's gestational age, it is essential that gestational age information (based on ultrasound or last menstrual period) is accurate. Overestimation of gestational age commonly results in a false positive Down syndrome risk assessment. Beaumont Laboratory has chosen to use a risk cut-off of 1:270 (age-related risk of a 35-year-old woman having a Down syndrome fetus). Other labs may use a different cut-off. Because this is a screen for Down syndrome, a number of positive results will be determined by further investigation to be false positives. However, use of the Quad screen should yield a lower number of false positives than the Triple 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.

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.

Open Neural Tube Defect (ONTD)
ONTD risk assessment is also reported as part of the Quad 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 Quad Screen is a screen used to determine the risk of a woman having a Down 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 syndrome can only be performed between 15 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.

Contacts

Last Updated

1/12/2023