A blood smear is often used as a follow-up test to abnormal results on a complete blood count (CBC) to evaluate the different types of blood cells. The test lends information on the number and shape of these cells, which further help doctors diagnose medical conditions based on the blood conditions like malaria. Thick and thin blood smears help doctors know the quantitative percentage of red blood cells that are infected (parasite density) and what type of parasites are present. Thick blood smears are most useful for detecting the presence of parasites, because they examine a larger sample of blood Thin blood smears help doctors discover what species of malaria is causing the infection