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Free DNA Fetal Kit<sup>®</sup> RhD


The « Free DNA Fetal Kit® RhD » is used to determine the fetal RHD genotype
in maternal blood from RhD-negative pregnant women.





Cell free fetal DNA (cffDNA) in the pregnant woman plasma may be detectable as early as the 7th gestational week (g.w.), but there is large variability among individuals related to the quantity and timing of fetal DNA in maternal plasma. Indeed, the range of plasma levels was 3.3 to 69.4 geq/ml and 76.9 to 769 geq/ml at the first and third trimester, respectively (Lo et al, 1998).

Because of the limited levels of cffDNA in plasma of pregnant woman, an efficient method of DNA extraction is required. Sensitivity of our kit has been evaluated in the course of CE marking and found to be between 50-100 geq/ml using a manual DNA extraction method (Qiagen columns), which is in the range of fetal DNA concentration in maternal plasma.

All the preanalytical steps must be checked, to ensure they meet the mandatory requirements according to the instructions for use. If the identification and tracability of samples are perfectly ensured, the sensitivity of the test is 100% on a blood maternal sample taken after 18 weeks of gestation.

An evaluation on the analysis of 120 plasma samples, from a documented library of plasmas collected from blood of RhD-negative pregnant women (C.H.I. Poissy St Germain - France, retrospective study) was performed using the kit Free DNA Fetal Kit® RhD (exons 5, 7 and 10). Five of these patients carried RHD silent gene in her genome. The gestational age of samples was as follows: 12-18 g.w. (27.5%), 19-26 g.w. (53.3%) and 27-35 g.w. (19.2%). The results were compared to the phenotype of the child at birth, with a correlation of 100%. No false negative results, defined by the absence of amplification of the three exons of the RHD gene were found in children with RhD positive phenotype.

Another evaluation on the analysis of 28 plasma samples, from a documented library of plasmas collected from blood of RhD-negative pregnant women (C.H.I. Poissy St Germain - France, retrospective study) was also performed using the kit Free DNA Fetal Kit® RhD (exons 5, 7 and 10) with the DX Real System BioRad. Two of these patients carried a RHD silent gene in her genome (16 and 19 g.w.). The gestational age of samples was as follows: 12-18 g.w. (50%), 19-26 g.w. (50%) and 27-35 g.w. (0%). No false negative result, defined by the absence of amplification of the three exons of the RHD gene was found in children with RhD positive phenotype.

Some automated DNA extraction methods can be used :

  • MagNapure Compact (Roche) : plasma volume 1000µl – élution volume 70µl
  • EasyMag (Biomérieux) : plasma volume 1000µl – élution volume 70µl
In conclusion, we assume that the medical device « Free DNA Fetal Kit® RhD » is a robust, specific and sensitive method to perform fetal RHD genotyping in maternal plasma.

 

CE IVD
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