Objectives: To characterize the number of granulocytes needed to count on peripheral smear to identify diagnostic anaplasmosis morulae.
Methods: Retrospective case study where the peripheral smears of 14 confirmed cases of anaplasmosis were examined. The granulocytes were counted up to 100 and 200 until a morula was identified. The mean counts of three pathologists were calculated to determine the minimum number of granulocytes needed to count for identifying diagnostic morulae.
Results: Morulae were identified before a count of 100 granulocytes in 11 (78.6%) cases and between 100 and 200 granulocytes in 3 (21.4%) cases. All 14 (100%) cases had morulae identified before counting 200 granulocytes.
Conclusions: Peripheral smears are a useful, cost-effective, and time-effective tool for diagnosing anaplasmosis. In positive cases, diagnostic morulae can be identified with a count of 200 granulocytes.
Keywords: Human granulocytic anaplasmosis; Morula; Peripheral blood smear.