Thread by @TransfusionWM

Next, Dr Edwin Massey talking on the implementation of foetal RHD screening @NHSBT #BSH2019

Dr Massey reminds us that _RHD_ is the gene which may or may not be translated into RhD or D protein #BSH2019

Assay for screening 'over diagnoses' D negativity. Performed after 11 weeks gestation #BSH2019

False negative rate <0.1%. Risk of D pos baby in a 'missed' woman who is then alloimmunised AND has a further baby who is affected is so low that screening is deemed effective #BSH2019

For women already alloimmunised, different screening test is used and at 16+/40 as false negative has greater consequences #BSH2019

Can also test ffDNA for kell but done at 20 and 28/40 due to higher risk of false negativity. Recent audit shows only 22% repeated at 28/40 and 0.5% false neg rate. False negatives not always fed back so likely underestimate #BSH2019

ffDNA not done for HPA typing at @NHSBT - right shifted like kell so high risk of false negative rate. Rare occurrence (20/year in England) means QA would not be feasible; samples sent to Sanquin #BSH2019

Not all ffDNA tests are equal says Dr Massey. Important to know the sensitivity of the test and understand implications of false negative to inform clinical decision making (the same as for any test!) #BSH2019