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QNatal Advanced™

Test code(s) 92777

Question 1. How is the QNatal Advanced™ test performed?

The QNatal Advanced test is performed on cell-free DNA (cfDNA) isolated from maternal blood. This cfDNA contains both maternal DNA as well as fetal DNA, which is derived from apoptotic placental cells (trophoblasts). Once isolated, the cfDNA is sequenced using massively parallel shotgun sequencing (MPSS); this is followed by quantitative bioinformatics analysis. In this way, the fetal copy number of chromosomes 21, 18, 13, X, Y and select microdeletion regions are calculated.

Question 2. What does the QNatal Advanced™ test detect?

QNatal Advanced can detect the most common autosomal fetal abnormalities: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). It can also detect abnormalities of the sex chromosomes. These include Turner syndrome (monosomy X) and Klinefelter syndrome (XXY) as well as XXX and XYY syndromes. In addition, microdeletions that are too small to be detected by standard cytogenetic analysis can be detected. These include microdeletions of chromosomes 1p (1p36 syndrome), 4p (Wolf-Hirschhorn syndrome), 5p (Cri-du-chat syndrome), 8q (Langer-Giedion syndrome), 11q (Jacobsen syndrome), 15q (Prader-Willi/Angelman syndromes), and 22q (DiGeorge syndrome).

Question 3. Can the fetal sex be determined?

Yes, fetal sex can be determined based on the presence or absence of Y chromosome cfDNA. However, if the clinician and patient do not wish to know the fetal sex, the healthcare provider can ‘opt out’ of having it reported.

Approved for use in the USA only, not for use in India or countries where it is illegal to do testing for gender.

Question 4. Are QNatal Advanced™ positive results diagnostic?

Like all noninvasive prenatal screening (NIPS) tests, the QNatal Advanced test does not provide a diagnostic result. Should a positive result be reported, a follow-up diagnostic test such as CVS or amniocentesis should be considered for definitive confirmation.

Question 5. Which disorders are not detected by the QNatal Advanced™ test?

Copy number abnormalities of chromosomes other than 21, 18, 13, X, or Y and abnormalities involving only a portion of a chromosome outside the microdeletion regions of interest are not detected. Additionally, the QNatal Advanced test, like other NIPS tests, cannot identify nonsyndromic congenital anomalies (i.e. birth defects). For example, a neural tube defect cannot be detected.

Question 6. When should the QNatal Advanced™ test be considered for a patient?

Consider testing patients at high risk for aneuploidy due to:

1.     Advanced maternal age (ie, 35 years of age or older at the time of delivery)

2.     Positive maternal serum screen (MSS)

3.     Abnormal ultrasound finding

4.     Positive personal or family history

Question 7. When would the QNatal Advanced™ test not be considered for a patient?

Testing should not be performed prior to 10 weeks gestational age.

Question 8. Can the QNatal Advanced™ test be performed on specimens from a multiple gestation pregnancy or a pregnancy with a donor ovum?

Yes, the QNatal Advanced test can be performed on specimens from both of these types of pregnancy.

Question 9. How does the QNatal Advanced™ test differ from CVS or amniocentesis?

The QNatal Advanced test is an NIPS test that can be performed as early as 10 weeks′ gestation and any time thereafter throughout pregnancy. It only requires two full tubes of blood (20 ml total) collected from a pregnant woman and therefore carries no risk for the fetus.

Question 10. How reliable are NIPS tests?

NIPS tests have been shown to be very reliable in validation studies.1-3

Table for Question 10 Positive Results, Sensitivity and Specificity

 

False positives and negatives do occur; causes include, but are not limited to, confined placental mosaicism, co-twin demise/vanishing twin, fetal mosaicism, maternal mosaicism, possible fibroids, and maternal malignancy.

Question 11. What is the turnaround time (TAT) for the QNatal Advanced™ test?

Results are typically reported within 7 to 10 days from time of specimen collection. Results are sent to the ordering physician’s office or to the electronic medical record (EMR).

Question 12. What is included in the QNatal Advanced™ test report?

The report includes a “negative” or “positive” result for trisomy 21, 18, and 13. When suspected, sex chromosome abnormalities and microdeletion syndromes will report as “increased risk” (unless microdeletion testing has been opted out). Fetal sex is reported as well, if not opted out. If the physician initially indicated that the fetal sex was not desired, he/she can request it later by contacting Quest Genomics Client Services at 866-GENE-INFO.

Question 13. When might I not receive a result?

Some specimens do not contain sufficient fetal cfDNA. Test results cannot be obtained, interpreted, or reported for these specimens. This can be due to several factors including, but not limited to, maternal obesity, inadequately filled tubes or only one tube. The test can be repeated using newly-collected maternal blood specimens. If no result is obtained on the second specimen, consideration of a diagnostic test may be appropriate.

Question 14. What is the follow up after a QNatal Advanced™ test?

No specific follow up is needed when the test is negative. However, if ultrasound examination of the fetus reveals anomalies, then further fetal studies might be indicated.4

Implications of a positive or increased risk result should be discussed with the patient. Diagnostic confirmation using amniocentesis or chorionic villus sampling (CVS) should be offered.4

 

References

  1. Palomaki GE, Kloza EM, Lambert-Messerlian GM, et al. DNA sequencing of maternal plasma to detect Down syndrome: an international clinical validation study. Genet Med. 2011;13:913-920.
  2. Palomaki GE, Deciu C, Kloza EM, et al. DNA sequencing of maternal plasma reliably identifies trisomy 18 and 13 as well as Down syndrome: an international collaborative study. Genet Med 2012;14:296-305.
  3. Canick, JA, Kloza EM, Lambert-Messerlian GM, et al. DNA sequencing of maternal plasma to identify Down syndrome and other trisomies in multiple gestations. Prenat Diag. 2012;32:730-734.
  4. Committee Opinion No. 640: Cell-free DNA screening for fetal aneuploidy. Obstet Gynecol. 2015;126(3):e31-e37. http://www.acog.org/-/media/Committee-Opinions/Committee-on-Genetics/co640.pdf?dmc=1&ts= 20151020T1255068154
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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Effective 10/28/2015 to present