P14 Hereditary Persistence of Fetal Haemoglobin Leading to Inappropriate Anti‐D Prophylaxis at Delivery

Fetal maternal haemorrhage (FMH) during pregnancy or delivery can lead to maternal RhD immunisation. Using the Kleihauer-Betke test, which detects fetal Hb (HbF) in cells, the necessary dose of prophylactic anti-D can be given to prevent immunisation. Hereditary persistence of fetal haemoglobin (HPFH) is a benign condition where HbF production continues into adult life. Classification is pancellular when HbF levels are elevated in all red cells or heterocellular when HbF is confined to a sub-population of cells. This is a rare condition, but these HbF cells may be mistaken for fetal cells in the Kleihauer test; we report such a case. Post-partum samples from an RhD negative woman and her RhD positive infant were tested the day following delivery. 500 iu of prophylactic anti-D was issued and a Kleihauer test performed to assess FMH volume and additional anti-D requirement. The FMH was estimated as 33 mL, however the HbFcells appeared as ‘intermediates’ or partially eluted, raising suspicion of HPFH. A total of 4500 iu of prophylactic anti-D was issued, since although HPFH was suspected, fetal origin of the HbF containing cells could not be excluded due to weekend unavailability of confirmatory testing. Subsequent flow cytometric (FACS) testing for FMH and haemoglobinopathy testing showed the patient to have previously undiagnosed HPFH. The timing of receipt and testing of these samples prevented confirmation of HPFH within the 72-h deadline for anti-D maximum effectiveness, leading to administration of precautionary additional anti-D doses. The likelihood of HPFH was considered because of the appearance of the HbF cells as ‘intermediates’, however not all laboratory staff will be familiar with such cells, particularly if they have not had experience in a haemoglobinopathy laboratory. This possibility should be highlighted.