Mean Platelet Volume (MPV)
The lab test that measures the volume of platelets is Mean Platelet Volume (MPV), which is routinely reported as part of the automated complete blood count using hematologic analyzers such as the Sysmex XN-10 or Hemavet 950. 1
What MPV Measures
- MPV quantifies the average size of platelets in femtoliters (fL), providing information about platelet production and turnover 1
- The measurement is performed automatically by impedance-based hematology analyzers during routine complete blood counts 2, 3
- Normal reference ranges are 7.2-10.8 fL in EDTA and 6.1-9.5 fL in citrate anticoagulated samples 4
Clinical Significance
- High MPV indicates increased platelet production and is associated with hyperdestructive causes when combined with thrombocytopenia, myeloproliferative disorders, thalassemia, or iron deficiency 2
- Low MPV suggests decreased production and correlates with cytotoxic drug use, marrow hypoplasia, sepsis, or chronic renal failure 2
- MPV improves diagnostic accuracy beyond platelet count alone, allowing detection of subtle disorders even when platelet counts are normal 2, 5
Critical Preanalytical Considerations
Timing is crucial: MPV should be measured 120 minutes after venipuncture for optimal accuracy 4
- Platelets swell over time - reaching maximum size at 120 minutes in EDTA and 60 minutes in citrate 4
- EDTA produces significantly larger MPV values (8.0 ± 0.8 fL) compared to citrate (7.0 ± 0.69 fL) 4
- The same anticoagulant must be used consistently within any study or serial measurements 6
- Samples should be processed promptly, as delays between collection and analysis affect platelet concentration and functional activity 6
Important Caveats
- Do not measure MPV in hemolyzed samples, or interpret results with extreme caution if unavoidable 6
- Cell fragments from erythrocytes or leukemic blasts can spuriously alter both platelet count and MPV; examination of platelet-rich plasma or manual phase counting may be required for accuracy 7
- MPV demonstrates an inverse relationship with platelet count in normal subjects, with the most pronounced changes at lower platelet counts 7
- While MPV is superior to manual megathrombocyte counting (sensitivity 80% at MPV ≥8.4 fL with 71% specificity), it cannot replace peripheral blood film examination in the complete evaluation of thrombocytopenia 5