Kleihauer testing Need not be abandoned

EDITOR, - We recently conducted a survey of Kleihauer testing in the North Western region, and our findings are similar to those of Jennifer K M Duguid and Imelda Bromilow,1 confirming the poor reproducibility and variability of the test as currently performed. We agree with Elizabeth A Letsky and Mahes de Silva that the reasons for the greater failure rate of prophylaxis with anti-D immunoglobulin in Britain compared with other countries require further investigation.2 We do not automatically conclude, however, that the recommended standard dose of 500 IU for postpartum prophylaxis in Britain should be reviewed.

Our study entailed a comparison of Kleihauer testing in hospital with analysis by flow cytometry for the investigation of fetomaternal haemorrhage when the perceived volume was over 4 ml of fetal red cells. Flow cytometry measured Rh D positive cells rather than fetal haemoglobin, which the Kleihauer test measures.

Over 12 months we analysed 43 maternal samples, and in 18 cases the results of the Kleihauer test were in considerable excess of the results of flow cytometry. When a calibrated microscope was used for the Kleihauer test this excess occurred in only 12 cases. In 15 cases the dose of anti-D immunoglobulin required was calculated from the result of flow cytometry. So far none of the women followed up six months after delivery has been immunised. A simple calculation showed that use of flow cytometry saved 55 000 IU of anti-D immunoglobulin in these 15 cases alone. The potential for savings in cases of fetomaternal haemorrhage exceeding 4 ml is obviously greater.

For routine testing the Kleihauer test is simple and inexpensive and can be performed by any hospital laboratory. Its poor reproducibility and variability do not imply that it should be abandoned and a higher standard dose of anti-D immunoglobulin given …