Utility of intradermal smear in the diagnosis of malaria

The objective of this preliminary study was to evaluate the usefulness of the intradermal smear test in the diagnosis of malaria. One hundred cases of suspected malaria (having received no prior antimalarials) were investigated. Both peripheral blood film (PBF) and intradermal smears (IDS) were simultaneously prepared and patients placed on antimalarial therapy. The slides were repeated for the next 2 days. At admission, 70 cases were positive on PBF--59 were Plasmodium falciparum (PF) and 11 were Plasmodium vivax (PV) whereas surprisingly 62 cases were positive on IDS at admission--61 were PF, one was PV. IDS identified two more cases of PF [P value (not significant)] but failed to identify any new cases of PV (P value NS). On subsequent days IDS positivity for PF was higher than for PBF (P < 0.05 for day 1 and P < 0.001 for day 2). However, the PV yield was poor for any further statistical evaluation on subsequent days. We conclude that IDS is simple, easy to perform, requires no special infrastructure compared to PBF, and is a helpful diagnostic tool in cases where malaria is strongly suspected but peripheral blood slides are repeatedly negative due to prior use of antimalarial therapy. IDS may be added to routine PBF in malaria (especially PF).