INTRINSIC AND ROUTINE QUALITY OF SERUM TOTAL POTASSIUM MEASUREMENT ASINVESTIGATED BY SPLIT SAMPLE MEASUREMENT WITH AN ION CHROMATOGRAPHY CANDIDATE REFERENCE METHOD

We evaluated the intrinsic quality of eight routine test systems for t he measurement of serum total potassium (K+), as well as the routine q uality of four of these systems, using a group of 60 single-donation s erum samples that had been certified with an ion chromatography refere nce method. The intrinsic quality of the tests was evaluated by analys is of the sera in the manufacturers' application laboratories under st rict internal quality control. The routine quality was evaluated by an alysis of the same sera in five (per system) routine laboratories unde r daily working conditions. The results of the study were interpreted in light of the most stringent specifications derived from the biologi cal variation of K+, which require limits of 6.3% for total error and 1.6% for systematic error. The study revealed that the intrinsic quali ty of all systems was excellent. None of the test systems yielded a su bstantial number of results outside the 6.3% total error limit, and on ly one test system exceeded the 1.6% systematic error limit. The major ity of the routine laboratories reproduced the manufacturers' intrinsi c quality. In particular, most laboratories satisfied the 6.3% total e rror limit. However, several laboratories exceeded the 1.6% systematic error limit. Generally, there was a considerable difference in qualit y between the participating laboratories. This showed that the major p roblems for serum K+ analysis (for samples with no unusual matrices an d with concentrations within the reference interval) are at the routin e laboratory.