Thick or thin blood film: counting one hundred WBCs (or more), report the number of parasites per 100 WBCs on the smear. In some cases (especially malaria) quantification of parasites yields clinically useful information. To quantify malaria parasites against RBCs, count the parasitized RBCs among 500-2,000 RBCs on the thin smear and express the results as % parasitemia.
For Plasmodium and Haemoproteus, scanning at 1000 x is necessary. Immersion oil is placed directly on the smear and the lens is lowered into the oil for scanning. (Be sure to use the immersion oil manufactured for the 1000x lens being used.) The oil will not harm the smear.