engleski

Critical points of acid-base balance and electrolytes testing in external quality control assessment in Croatia

Background: External quality assessment (EQA) for analysis of pH, blood gases and electrolytes in Croatia is conducted through two modules with two different sample types. The aim of this study was to present inter- laboratory comparability of these analyses and to identify critical points in sample types used in EQA and/or laboratory work. Materials and Methods: Control samples used during three cycles in 2014 and one in 2015 were commercial, but different origin (sample A, human origin and sample B, aqueous solution) in three different concentration ranges (normal, pathological low and high).They were used in ‘one cycle-one range’ manner. According to Tukey's model outliers were excluded and mean, standard deviation (SD) and coefficient of variation (CV) were calculated. According to quality specifications established in Croatian EQA, the allowable CVs were as follows: CVpH=±1%, CVpO2=±12%, CVpCO2=±12%, CVNa+=±3%, CVK+=±5% and CVCa2+=±5%. Criteria used in assessing preferable sample type and laboratory work were CVs and success rate (SR) of all participating laboratories, regardless of method and instrument. Results: Both samples indicated equal presence of unacceptable CVs according to established criteria (5/24 ; 21%) for following parameters: pO2 (low range-2A, B), ionized potassium (low range-A, B ; high range-B), ionized calcium (low range–B ; high range–A, B). For all these parameters, SR was unaceptable (<67%, depending of analysis). Normal concentration range regardless of the sample type for all analysis indicates acceptable CVs and good inter- laboratory comparability. pH, pCO2 and ionized sodium in all concentration ranges and for both sample types had acceptable CVs and high SR. Conclusions: According to our results, sample type does not represent a critical point in the implementation of EQA for examined analytes. Our observational study indicates that a critical point is pathological range of both commercial controls. On the other hand, preanalytical and analytical factors in laboratory work should also be concerned.

external quality control, acid base balance, electrolytes, inter-laboratory comparability

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