Correction and reporting of potassium results in haemolysed samples

Abstract

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.