POINT OF CARE ANALYSIS OF ELECTROLYTES AND CALCIUM IN CRITICALLY ILL PATIENTS: COMPARISON WITH CENTRAL LABORATORY INSTRUMENTS DATA

Last generation Point of Care Testing (POCT) emogas-analyzers provide measurements of electrolytes and Ca2+. Therefore the appropriate use of POCT systems assume a very important clinical significance, allowing a continuous monitoring of those parameters in critically ill patients. Verifying the alignment of POCT results with those obtained from Central Laboratory(CLab) instruments is essential. In this study we compared POCT Na+, K+, Cl-, Ca2+ results with those measured with CLab instruments. MATERIALS AND METHODS Instruments: A(RapidPoint500,Siemens), B(DxC880,BeckmanCoulter), C(Modular,Roche) used in POCT, emergency Lab and routine Lab, respectively. Methods: Na+, K+, Cl- by direct ion-selective electrode(ISE) method in A and by indirect ISE method in B and C; Ca2+ by direct ISE method in A, while B and C measured total calcium by colorimetric method, then the Ca2+ values were calculated. Samples: 36 serum samples were collected and analyzed by A, B and C; for the same 36 patients also heparin plasma samples were collected and analyzed by A. Statistics: Passing-Bablok regression, Bland-Altman, R coefficient. RESULTS OF COMPARISON STUDIES Na+: slope=1.06,1.07,1.05; intercept=-9.83,-11.4,-6.18; R=0.96,0.96,0.93; Syx=1.0,1.09,1.44 for AvsB, AvsC and CvsB respectively. K+: slope=1.04,1.02,1.0; intercept=-0.13,-0.12,0.1; R=0.99,0.99,0.99 Syx=0.045,0.045,0.073 for AvsB, AvsC and CvsB respectively. Cl-: slope=0.98,1.0,1.03; intercept=1.05,1.0,-4.87; R=0.90,0.89,0.93; Syx=1.28,1.22,1.07 for AvsB, AvsC and CvsB, respectively. Ca2+slope=1.09,0.91,1.29; intercept=-0.41,0.37,-1.30; R=0.75,0.76,0.85; Syx=0.20,0.21,0.13 for AvsB, AvsC and CvsB, respectively. Plasma vs serum correlations: Na+, K+, Cl- and Ca2+ R=0.98,0.98,0.93,0.82 respectively. CONCLUSION Correlations data between A, B and C serum samples showed an excellent result for K+, a good result for Na+ and Cl- and a less acceptable value for Ca2+. In addition, we observed a good correlation between plasma and serum samples for Na+, K+and Cl-, but less for Ca2+. We consider that verifying the correlation between POCT and CLab instruments and informing clinicians about the observed results is essential to reduce errors and improve quality and patient safety. Point of care testing BMJ 2001;322:1285–8