Normal Platelet Levels
Normal platelet count ranges from 150,000 to 450,000 platelets per microliter (μL) of blood. 1, 2
Standard Reference Range
- The established normal range is 150,000-450,000/μL in adults, representing the threshold beyond which thrombocytopenia (low) or thrombocytosis (high) is diagnosed 1, 2
- In healthy pediatric subjects, normal platelet count ranges between 250,000/μL and 450,000/μL, which is slightly higher than the adult lower threshold 3
- Some sources cite a narrower range of 150,000-400,000/μL as the typical concentration in healthy humans 4
Clinical Significance of Deviations
Thrombocytopenia (Low Platelet Count)
- Thrombocytopenia is defined as platelet count <150,000/μL 5
- Bleeding risk increases progressively as counts decline: counts <5,000/μL are associated with frequent and severe hemorrhage, 5,000-10,000/μL with moderate bleeding risk, 10,000-20,000/μL with bleeding in 8% of hospital days, and >20,000/μL with bleeding in only 4% of hospital days 1
- Only 10,000 platelets/μL are actually needed for basic vessel wall repair and wound healing, though this is far below the normal range 4
Thrombocytosis (High Platelet Count)
- Thrombocytosis is defined as platelet count >450,000/μL (>2 standard deviations above mean) 1, 3
- Mild thrombocytosis: 500,000-700,000/μL 3
- Moderate thrombocytosis: 700,000-900,000/μL 3
- Severe thrombocytosis: >900,000/μL 3
- Extreme thrombocytosis: >1,000/μL 3
Key Clinical Caveats
- Platelet count alone is a weak indicator of bleeding or thrombotic risk—platelet function is equally important, particularly in trauma and uremic patients 1
- Modern automated cell counters are accurate at low platelet counts, but modest variations can occur due to technological limitations, so clinical context should guide transfusion decisions rather than precise trigger levels 6
- The normal range applies to circulating platelets; additional platelets are sequestered in the spleen and may be released during physiologic stress 5