Better results born of better science
Proprietary, noninvasive technology enables the detection and analysis of circulating cell-free fetal (ccff) nucleic acids (DNA) in a pregnant woman’s blood sample. Rather than harvesting placental tissue cells or entering the uterus to sample the amniotic fluid, circulating cell-free fetal nucleic acid can be obtained from maternal blood.
Ccff DNA in maternal plasma is thought to derive from apoptosis of placental and fetal cells and possibly through the breakdown of fetal cells in circulation22 , 23 , 24. Recent studies have shown >10% circulating fetal DNA concentration in maternal plasma9.
This test method is designed to detect circulating cell-free fetal DNA from maternal blood and examine multiple regions of the gene that is known to be the most common genetic basis of RhD negative phenotypes. The test interrogates targets within 3 exons located on the RHD gene in chromosome one. The test also incorporates male-specific targets on the Y chromosome because it has been demonstrated that Rh alloimmunization occurs more frequently in male fetuses23. There are quality control metrics added to the reaction to ensure accuracy and a quality control test is used to facilitate the distinction between maternal and female fetal DNA.
Summary of Test Design
This test detects targets within 3 exons of the RHD gene located on chromosome one.
Assay Targets: Exons 4, 5, 7
Psi (Ψ) pseudogene in exon 4
4 Assay Controls: 3 targets on Y chromosome (SRY, TTTY, DBY)
- Extraction Control (TGIF)
- A positive control for successful DNA extraction must be detected to issue a report. Presence or absence of RHD exon targets determines if the specimen will be reported as RHD positive or negative.
- All RHD negative results are confirmed on a second 4 mL aliquot of submitted plasma.
- For specimens that generate a fetal RHD negative female result (and thus in need of differentiating mother and fetus), a fetal identifier (FI) control is performed to compare maternal and fetal genotypes.
- In the FI control, 92 potentially informative DNA markers (single nucleotide polymorphisms) are examined for markers present in the fetal DNA fraction that are absent in the maternal genomic DNA fraction. These markers must therefore be paternally inherited. If six or more markers are observed, the RHD negative female result can be attributed to the true presence of fetal DNA.
An easy-to-read one page lab reported will be faxed to your office.