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Test Code QUAD Quad Screen (Second Trimester) Maternal, Serum

Reporting Name

QUAD SCRN (2nd Tri) MATERNAL, S

Useful For

Prenatal screening for open neural tube defect (alpha-fetoprotein only), Down syndrome (alpha-fetoprotein, human chorionic gonadotropin, estriol, and inhibin A) and trisomy 18 (alpha-fetoprotein, human chorionic gonadotropin, and estriol)

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Container/Tube: 

Preferred: Red top

Acceptable: Serum gel

Specimen Volume: 1 mL

Collection Instructions:

1. Do not draw specimen after amniocentesis, as this could affect results.

2. Immediately spin down.

Additional Information:

1. For an assessment that includes neural tube defect results, gestational age must be between 15 weeks, 0 days and 22 weeks, 6 days.

2. Assessments for Down syndrome and Trisomy 18 only are available between 14 weeks, 0 days and 22 weeks, 6 days.

3. Initial or repeat testing is determined in the laboratory at the time of report and will be reported accordingly. To be considered a repeat test for the patient, the testing must be within the same pregnancy and trimester, with interpretable results for the same tests, and both tests are performed at Mayo Clinic.

4. Patient education brochures in English (T522) and Spanish (T534) are available upon request.


Specimen Minimum Volume

0.75 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Frozen  90 days

Reference Values

NEURAL TUBE DEFECTS

An AFP multiple of the median (MoM) <2.5 is reported as screen negative. AFP MoMs ≥2.5 (singleton and twin pregnancies) are reported as screen positive. 

 

DOWN SYNDROME

Calculated screen risks <1/270 are reported as screen negative, risks ≥1/270 are reported as screen positive.

 

TRISOMY 18

Calculated screen risks <1/100 are reported as screen negative, risks ≥1/100 are reported as screen positive.

 

An interpretive report will be provided.

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-5 p.m.

Saturday; 6 a.m.-1 p.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81511-Fetal congenital abnormalities, biochemical assays of four analytes (AFP, uE3, hCG [any form], DIA) utilizing maternal serum, algorithm reported as a risk score (may include additional results from previous biochemical testing)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
QUAD QUAD SCRN (2nd Tri) MATERNAL, S 48800-7

 

Result ID Test Result Name Result LOINC Value
7058 Recalculated Maternal Serum Screen 49092-0
3009 Collection Date 33882-2
7823 Birthdate 21112-8
7834 Calculated age at EDD 43993-5
26717 Maternal Weight 29463-7
26718 Maternal Weight 29463-7
IDD Insulin dependent diabetes 44877-9
RACE Black race 32624-9
MULTF Number of Fetuses 55281-0
IVFP IVF pregnancy 47224-1
7816 Gestation (GA) by U/S 11888-5
7817 Date of U/S 34970-4
10054 EDD by U/S scan 11781-2
2907 Last Menstrual Period (LMP) 8665-2
7753 EDD by LMP 11779-6
7206 Gestation (GA) by dates 11885-1
7200 Date of estimate 80395-7
7201 Gestation (GA) by physical exam 11884-4
7202 Date of physical exam No LOINC Needed
7203 GA on collection by U/S scan 11888-5
7204 GA on collection by dates 11885-1
7205 GA on collection by physical exam 11884-4
7830 GA used in risk estimate 21299-3
10351 AFP 31993-9
10352 uE3 27259-1
10353 hCG, TOTAL 2116-2
10354 INHIBIN 2478-6
10334 Down syndrome screen risk estimate 43995-0
10335 Down syndrome maternal age risk 49090-4
10337 Trisomy 18 screen risk estimate 43994-3
10356 INTERPRETATION 59462-2
10248 Additional comments 55107-7
10357 RECOMMENDED FOLLOW UP 80615-8
10358 GENERAL TEST INFORMATION 62364-5
32284 Other Information 52535-2

Clinical Information

Multiple marker serum screening has become a standard tool used in obstetrical care to identify pregnancies that may have an increased risk for certain birth defects, including neural tube defects (NTDs), Down syndrome, and trisomy 18. The screen is performed by measuring analytes in maternal serum that are produced by the fetus and the placenta. The analyte values along with maternal demographic information such as age, weight, gestational age, diabetic status, and race are used together in a mathematical model to derive a risk estimate. The laboratory establishes a specific cutoff for each condition, which classifies each screen as either screen-positive or screen-negative. A screen-positive result indicates that the value obtained exceeds the established cutoff. A positive screen does not provide a diagnosis, but indicates that further evaluation should be considered.

 

Analytes:

Alpha-Fetoprotein (AFP)

AFP is a fetal protein that is initially produced in the fetal yolk sac and liver. A small amount also is produced by the gastrointestinal tract. By the end of the first trimester, nearly all of the AFP is produced by the fetal liver. The concentration of AFP peaks in fetal serum between 10 to 13 weeks. Fetal AFP diffuses across the placental barrier into the maternal circulation. A small amount also is transported from the amniotic cavity.

 

The AFP concentration in maternal serum rises throughout pregnancy, from a nonpregnancy level of 0.2 to about 250 ng/mL at 32 weeks gestation. If the fetus has an open NTD, AFP is thought to leak directly into the amniotic fluid causing unexpectedly high concentrations of AFP. Subsequently, the AFP reaches the maternal circulation, thus producing elevated serum levels. Other fetal abnormalities such as omphalocele, gastroschisis, congenital renal disease, esophageal atresia, and other fetal distress situations such as threatened abortion, and fetal demise also may show AFP elevations. Increased maternal serum AFP values also may be seen in multiple pregnancies and in unaffected singleton pregnancies in which the gestational age has been underestimated.

 

Lower maternal serum AFP values have been associated with an increased risk for genetic conditions such as trisomy 21 (Down syndrome) and trisomy 18.

 

Estriol (uE3)

Estriol, the principal circulatory estrogen hormone in the blood during pregnancy, is synthesized by the intact feto-placental unit. Estriol exists in maternal blood as a mixture of the unconjugated form and a number of conjugates. The half-life of unconjugated estriol in the maternal blood system is 20 to 30 minutes because the maternal liver quickly conjugates estriol to make it more water soluble for urinary excretion. Estriol levels increase during the course of pregnancy. Decreased unconjugated estriol has been shown to be a marker for Down syndrome and trisomy 18. Low levels of estriol also have been associated with overestimation of gestation, pregnancy loss, Smith-Lemli-Opitz, and X-linked ichthyosis (placental sulfatase deficiency).

 

Human Chorionic Gonadotropin (Total Beta-hCG: ThCG)

hCG is a glycoprotein consisting of 2 noncovalently bound subunits. The alpha subunit is identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH), while the beta subunit has significant homology to the beta subunit of LH and limited similarity to the FSH and TSH beta subunits. The beta subunit determines the unique physiological, biochemical, and immunological properties of hCG.

 

The CGA gene (glycoprotein hormones, alpha polypeptide) is thought to have developed through gene duplication from the LH gene in a limited number of mammalian species. hCG only plays an important physiological role in primates (including humans), where it is synthesized by placental cells, starting very early in pregnancy, and serves to maintain the corpus luteum, and hence, progesterone production, during the first trimester. Thereafter, the concentration of hCG begins to fall as the placenta begins to produce steroid hormones and the role of the corpus luteum in maintaining pregnancy diminishes.

 

Increased total hCG levels are associated with Down syndrome, while decreased levels may be seen in trisomy 18. Elevations of hCG also can be seen in multiple pregnancies, unaffected singleton pregnancies in which the gestational age has been overestimated, triploidy, fetal loss, and hydrops fetalis.

 

Inhibin A

Inhibins are a family of heterodimeric glycoproteins, primarily secreted by ovarian granulosa cells and testicular Sertoli cells, which consist of disulfide-linked alpha and beta subunits. While the alpha subunits are identical in all inhibins, the beta subunits exist in 2 major forms, termed A and B, each of which can occur in different isoforms. Depending on whether an inhibin heterodimer contains a beta A or a beta B chain, they are designated as inhibin A or inhibin B, respectively. Together with the related activins, which are homodimers or heterodimers of beta A and B chains, the inhibins are involved in gonadal-pituitary feedback and in paracrine regulation of germ cell growth and maturation. During pregnancy, inhibins and activins are produced by the feto-placental unit in increasing quantities, mirroring fetal growth. Their physiological role during pregnancy is uncertain. They are secreted into the coelomic and amniotic fluid, but only inhibin A is found in appreciable quantities in the maternal circulation during the first and second trimesters.

 

Maternal inhibin A levels are correlated with maternal hCG levels and are abnormal in the same conditions that are associated with abnormal hCG levels (eg, inhibin A levels are typically higher in Down syndrome pregnancies). However, despite their similar behavior, measuring maternal serum inhibin A concentrations in addition to maternal serum hCG concentrations further improves the sensitivity and specificity of maternal multiple marker screening for Down syndrome.

Interpretation

Neural Tube Defects (NTD):

A screen-negative result indicates that the calculated alpha-fetoprotein (AFP) multiple of the median (MoM) falls below the established cutoff of 2.50 MoM. A negative screen does not guarantee the absence of NTD.

 

A screen-positive result indicates that the calculated AFP MoM is ≥2.50 MoM, and may indicate an increased risk for open NTD. The actual risk depends on the level of AFP and the individual's pretest risk of having a child with NTD based on family history, geographical location, maternal conditions such as diabetes and epilepsy, and use of folate prior to conception. A screen-positive result does not infer a definitive diagnosis of NTD, but indicates that further evaluation should be considered. Approximately 80% of pregnancies affected with NTD have elevated AFP, MoM values >2.5.

 

Down Syndrome and Trisomy 18:

A screen-negative result indicates that the calculated screen risk is below the established cutoff of 1/270 for Down syndrome and 1/100 for trisomy 18. A negative screen does not guarantee the absence of trisomy 18 or Down syndrome.

 

When a Down syndrome second trimester risk cutoff of 1/270 is used for follow-up, the combination of maternal age, AFP, estriol, hCG, and inhibin A has an overall detection rate of approximately 77% to 81% with a false-positive rate of 6% to 7%. In practice, both the detection rate and false-positive rate increase with age. The detection rate ranges from 66% (early teens) to 99% (late 40s), with false-positive rates of between 3% and 62%, respectively. The detection rate for trisomy 18 is 60% to 80% using a second trimester cutoff of 1/100.

 

Follow-up:

Upon receiving maternal serum screening results, all information used in the risk calculation should be reviewed for accuracy (maternal date of birth, gestational dating, etc). If any information is incorrect, the laboratory should be contacted for a recalculation of the estimated risks.

 

Screen-negative results typically do not warrant further evaluation.

 

Ultrasound is recommended to confirm dates for NTD or trisomy 21 screen-positive results. Many pregnancies affected with trisomy 18 are small for gestational age. Recalculations that lower the gestational age may decrease the detection rate for trisomy 18. If ultrasound yields new dates that differ by at least 7 days, a recalculation should be considered. If dates are confirmed, high-resolution ultrasound and amniocentesis (including amniotic fluid AFP and acetylcholinesterase measurements for NTD) are typically offered.

Clinical Reference

1. Christensen RL, Rea MR, Kessler G, et al: Implementation of a screening program for diagnosing open neural tube defects: selection, evaluation, and utilization of alpha-fetoprotein methodology. Clin Chem 1986;32:1812-1817

2. Wald NJ, Densem JW, Smith D, Klee GG: Four marker serum screening for Down's syndrome. Prenat Diagn 1994;14:707-716

3. Florio P, Cobellis L, Luisi S, et al: Changes in inhibins and activin secretion in healthy and pathological pregnancies. Mol Cell Endocrinol 2001;180:123-130

4. Benn PA: Advances in prenatal screening for Down syndrome: I. General principles and second trimester testing. Clin Chim Acta 2002;324:1-11

5. Wald NJ, Cuckle HS, Densem JW, et al: Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in pregnancies with insulin-dependent diabetes: implications for screening for Down's syndrome. Br J Obstet Gynaecol 1992;99:51-53

6. American College of Obstetricians and Gynecologists: Screening for fetal chromosomal abnormalities. Obstet Gynecol 2007;109:217-227

7. Malone FD, Canick JA, Ball RH, et al: First-trimester or second-trimester screening, or both, for Down’s syndrome. N Engl J Med 2005;353:2001-2011

8. Wald NJ, Rodeck C, Hackshaw AK, et al: SURUSS in perspective. Semin Perinatol 2005;29:225-235

Analytic Time

1 day

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross OK

Icterus

NA

Other

NA

 

Method Name

Immunoenzymatic Assay

Testing Algorithm

See Prenatal Aneuploidy Screening and Diagnostic Testing Options in Special Instructions

Forms

Second Trimester Maternal Screening Alpha-Fetoprotein (AFP)/QUAD Screen Patient Information (T595) is required in Special Instructions.