Correction and reporting of potassium results in haemolysed samples

Potassium is usually the most important analyte affected by in vitro haemolysis and the result obtained may falsely indicate or disguise a life-threatening abnormality and so give rise to inappropriate treatment. The purpose of the study was to provide a solution to the problem of reporting potassium on haemolysed samples, taking into account both clinical needs and analytical concerns (inter-individual and inter-sample variability).

Using a new procedure that mimics the collection process in an actual clinical setting, haemolysed samples were prepared from 41 volunteers with a range of inter-individual factors - haemoglobin 80-173 g/L, red blood cells 2.42-6.77 x 10(12)/L, leucocytes 3.0-306 x 10(9) /L and platelets 31-710 x 10(9)/L - in order to develop a more accurate correction equation using a haemolytic index (HI) corresponding to g Hb/L in plasma.

The mean (range) potassium increase was 0.0036 mmol/L (0.0029-0.0053 mmol/L) per unit HI. The following equation was developed to estimate potassium increase per HI, in order to compensate approximately for potassium leakage in haemolysed samples: Corrected K+ = Measured K+ -(HI x 0.004).

The balanced solution is this: instead of reporting the post-haemolysis corrected potassium result a qualitative comment is given, indicating the likely range of the potassium concentration. If the potassium result is in a critically low or high range, it is communicated promptly to the requesting clinician.