Complete blood count (CBC) tests are rapid, inexpensiveand universally available, and often aid primary clinicianswith decision making about patients with severaldisorders. Thus the rapid availability of the results of CBCcould provide considerable advantage for both patientsand clinicians. Furthermore, physicians can also avoidunnecessary peripheral blood smear examination usingCBC parameters. Many hematology analyzers, which enabledus simultaneously, measure several different CBCparameters, are available for early diagnosis. Herein theimpact of both pre and post analytic variations on the interpretationof the CBC results with case reports are reviewedin the light of the latest literature.Key words: Complete blood count, interpretation