A comparative study of thick and thin blood films in the diagnosis of scanty malaria parasitaemia.

In an attempt to explain the shortcomings of the routine thick-film examination in the diagnosis of scanty malaria parasitaemias, a direct comparison, in terms of positivity and parasite counts, was made between the results of routine thick-film study and long-term examination of thin films taken at the same time from the same individuals. Calculation of the average thickness of the thick and thin films prepared allowed these comparative results to be corrected according to the actual volume of blood examined. From these corrected figures it was observed that both parasite counts and positivity were significantly higher in the thin-film series, and it has been deduced that heavy losses in parasites, varying from 60% to 90%, occurred during the dehaemoglobinization and staining of thick films.The epidemiological implications of this finding in malaria practice are discussed. Emphasis is laid on the importance of further research in order to improve the sensitivity of the routine thick film in the diagnosis of the scanty parasitaemias met with in the later stages of malaria-eradication programmes.