Interference of plasma fluorophores on the red blood cell zinc protoporphyrin: haemoglobin ratio as determined on a haematofluorimeter.

Direct measurement of the zinc protoporphyrin:haemoglobin ratio (ZPP:Hb ratio) in blood samples is performed by using a haematofluorimeter. Interference by non-specific fluorophores can be eliminated by removing the plasma and making the measurement on washed red blood cells (RBCs). After re-suspending RBCs in isotonic saline, haematofluorimeter readings for the ZPP:Hb ratios revealed higher stability in the course of time whereas a good relationship was found with results obtained by application of an extraction method. Separate reference ranges were established for adult male and female subjects. After washing, the mean values calculated for ZPP:Hb ratios of subjects belonging to the reference groups demonstrated a reduction of 0.04 mumol ZPP mol Hb, corresponding with approximately 30%. In the patients' group, application of washing resulted in a variable decrease of ZPP:Hb ratios.