A quantitative approach to the relationship between Wuchereria bancrofti microfilaria counts by venous blood filtration and finger-prick blood films.

Counts of nocturnally periodic Wuchereria bancrofti microfilariae (mf) in 20 mm3 finger-prick blood films were compared with membrane counts after filtration of 1 ml of venous blood for their efficacy in determining the prevalence of Bancroftian filariasis. The technique used for spreading and staining the blood films was critically important to the sensitivity of this screening procedure. There was good agreement between the 2 methods. Four statistical approaches were used to measure the correlation between the 2 sampling methods: 2 linear regression methods using untransformed and transformed data, and 2 non-parametric rank correlation methods. Based on the statistical analyses, this study strongly supports the general observation that finger-prick blood samples tend to contain more mf than equivalent volumes of venous blood, at mf densities high enough to be detectable by the finger-prick technique. It also demonstrates that finger-prick samples provide good estimates of mf densities and prevalence of infection except in areas of very low mf densities, where the membrane filtration method would provide a more accurate estimate of prevalence. Regression analyses using untransformed and transformed data, and the rank correlation tests, demonstrated a strong statistically significant correlation (P less than 0.001) between venous and finger-prick mf counts.