Referring samples to RCI for Fetal Maternal Haemorrhage (FMH) by Flow Cytometry (FC)

When sending samples to RCI for measurement of FMH volume, it is important to send a separate maternal EDTA sample that has not been used for other tests. Samples should not be centrifuged or tested on a blood group analyser.

The larger fetal cells separate from maternal cells during centrifugation. This can affect the accuracy of FMH testing if the same sample is used, as it is difficult to re-mix effectively. If the sample has already been used for blood grouping, the larger fetal red cells sitting closer to the plasma/red cell interface may have been sampled preferentially, reducing the volume remaining and leading to underestimation of the fetal bleed. See the recently updated British Society for Haematology guidance

If only one maternal sample is available and this has been centrifuged, please discuss the case with the RCI laboratory. If the sample is irreplaceable (e.g. anti-D immunoglobulin has already been given, or the woman has already been discharged) then testing under concession may be considered, but the results will be issued with a caution about their accuracy. Clinical advice can be sought from a NHSBT consultant (telephone numbers are listed in appendix 1 of the RCI user guide).

Wisdom Musabaike - Assistant Director of RCI