Arterial versus venous potassium: clinical implications.

A difference between potassium concentrations in arterial plasma and venous serum was evaluated. The difference was 0.5 mM/litre, with a range of 0.1 to 1.1 mM/liter. Multiple factors operating primarily upon the venous sample are responsible for this difference. The value for arterial plasma potassium is stable and preferable, but a revised normal for arterial plasma K+ is necessary.