Platelet count measures the number of platelets in circulation, with a typical reference range of about 150,000–400,000/μL. Platelets are essential for primary clot formation and vascular repair.

Low platelets increase bleeding risk, though the degree of risk depends on how low the count is and the overall clinical context. High platelets may be reactive—seen with inflammation, infection, or iron deficiency—or less commonly due to a bone marrow disorder. In healthy individuals, mild abnormalities are often incidental, but persistent changes deserve follow-up.