Potassium Reference Intervals: A Need for Separate Reference Intervals for Serum and Plasma

Although potassium measurements are relatively well standardized, laboratory RIs for potassium vary considerably. Most laboratories use the same RI for serum and plasma potassium, although serum and plasma measurements usually differ by 0.2-0.4 mmol/L, exceeding acceptable limits for bias. Consequently, serum-derived RIs are suboptimal RIs for plasma. Testing of plasma specimens is common in acute care settings, but most laboratory RIs and clinical guidelines are based on serum measurements. Outcome studies show that there is a narrow optimal range for potassium levels and that outcomes improve with careful management of potassium levels. Separate RIs and clinical guideline values for plasma and serum potassium offer better assessment of potassium levels.