The basis for common reference intervals for serum potassium

In order to investigate the relevance of the currently used lower reference limit for S-Potassium in Danish hospital laboratories, analytical bias in the measurement of S-Potassium was compared with the lower reference limit in each of 52 Danish hospital laboratories. The acceptable bias range was estimated according to Gowans et al on the basis of the result of two different reference sample groups. The estimated acceptable 0.95 bias range was 0.24 mmol/L, so the observed bias range of 0.23 mmol/L was within this limit. As all preanalytical errors tend to increase the measured S-Potassium, all acceptable bias should be in the direction of decreasing the measured value. It can be concluded that analytical performance allows for more uniform (even common) reference interval(s) in all Danish and perhaps Nordic hospital laboratories, provided that preanalytical errors can be controlled.