False positive Kleihauer results: an unusual cause in a postnatal patient in remission from acute myeloid leukaemia.

A 34-year-old woman, in remission from acute myeloid leukaemia, had a positive postnatal Kleihauer result. Following our standard local protocol for positive Kleihauer tests in Rh-D negative patients, the specimen was referred for confirmatory testing, which proved the result to be false positive. Hereditary persistence of foetal haemoglobin was excluded as a Kleihauer test performed in a pregnancy prior to the development of leukaemia was negative. Further testing confirmed mild elevation of foetal haemoglobin (HbF) and increased F-cells. Elevated-HbF levels have been widely reported in patients with haematological malignancy. In this case, the patient was confirmed to be in a true molecular remission from leukaemia and yet appeared to have a residual clonal population of HbF erythrocytes; the significance of this finding remains unclear. This case also highlights the importance of confirmatory testing of suspected foeto-maternal haemorrhage, as not all positive Kleihauer tests are true positives.