Potassium reference range is reported in which unit?

• A. mg/dL
• B. mEq/L
• C. mmol/L
• D. g/L

Answer: (C)

Concentrations of potassium in blood are expressed as a molar quantity per liter, not as a mass. Using millimoles per liter (mmol/L) directly reflects how many potassium ions are present in a given volume, which is the most physiologically relevant way to assess electrolyte status. For a monovalent ion like potassium, milliequivalents per liter (mEq/L) would match mmol/L, but modern clinical practice standardizes on mmol/L for consistency across electrolytes and to avoid any confusion tied to atomic weight. Mass-based units such as mg/dL or g/L depend on the ion’s weight and don’t translate cleanly to ion concentration, making comparisons less straightforward. So the reference range for potassium is reported in mmol/L (commonly around 3.5–5.0 mmol/L in adults).