The aim of this retrospective study was to determine whether variations in the enumerated white cell contamination of leucocyte-depleted products was caused by the filter batch, the processing centre or by counting technology related issues. The influence of donor variation is also considered. The results suggest that for some red cell processes, variation is mainly the result of counting technology differences. Other products do not display similar trends though all leucodepletion processes may give rare high white count failures due to donor related issues, though defective filter batch cannot be excluded requiring continual review.