RhD/SRY plasma DNA sensitivity standard for non-invasive maternal screening

The determination of foetal RHD genotype using foetal DNA contained in the maternal circulation is increasingly used to manage pregnancies at risk for haemolytic disease of the newborn (HDN) caused by maternal anti-D (OMIM #111680). 

The test offers significant advantages over previous procedures which relied on foetal DNA extracted from amniotic fluid or chorionic villi obtained from invasive procedures.

The detection of RHD sequences is usually carried out by quantitative PCR techniques (QPCR) and a positive result is used to predict foetal D status.

At the same time laboratories usually test for sequences unique to the Y chromosome, where any positive result indicates that (male) foetal DNA has been extracted and was present in the sample. However, there is no confirmatory test for female foetuses.

The test is becoming increasingly reliable and routine clinical services have been established in some centres. However, laboratories currently have no materials with which to determine the performance of their tests. 

We are in the process of developing a material that can be used as a minimum sensitivity reagent.

The material consists of RhD-positive male plasma diluted in an excess of RhD-negative female plasma. It is intended that the material will be used as a QPCR minimum sensitivity standard. It will be of importance for laboratories setting up new in-house methods or commercial techniques for the detection of RHD sequences and for validating existing techniques after a change of reagents, operator or equipment.

Reference

Metcalfe P et al. (2012) An international reference reagent for the detection of RHD and SRY DNA in plasma. Vox Sanguinis 102: 243-249 

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