A statistical study of the sensitivity of the haematocrit centrifuge technique in the detection of trypanosomes in blood

The sensitivity of the haematocrit centrifuge technique in detecting trypanosomes was investigated using both old laboratory and freshly isolated strains.Two alternative methods of analysing the results are suggested, based on the binomial and Poisson distributions.The analysis shows that the H.C.T. can detect about 85% of the trypanosomes present in capillary samples of Trypanosoma brucei, T. rhodesiense and T. evansii, and 30% of T. congolense group trypanosomes. The technique is therefore much more sensitive than previous wet preparation or thick smear techniques.Graphs are provided showing the minimum number of tubes that would have to be examined for 95% and 99% detection of low infections (i.e., in the range up to 500 trypanosomes per ml.).Analysis of the results using the Poisson model includes details of a simple method that estimates the efficiency of the H.C.T. from the slope of a graph.The present results do not show any significant relationship between the probability that a trypanosome will be missed by the H.C.T. and trypanosome density.