Nowadays, turbidimetric platelet aggregation is the gold standard test for evaluation of platelet function, and platelet indices including mean platelet volume (MPV) were not correlated with the results of turbidimetric platelet aggregation. Also, measurement of MPV cannot be performed completely because of standardization problems. MPV progressively increases with time in anticoagulated samples. Optimal measurement time with citrate should be 60 minutes after venipuncture in the determination of MPV. Another important problem regarding MPV measurement is that different technologies reveal different results up to 40%. As a result, MPV may not be a useful predictor for arterial stiffness in newly diagnosed hypertensive patients.