A comparison of measurements of sodium, potassium, haemoglobin and creatinine between an Emergency Department-based point-of-care machine and the hospital laboratory.

Blood gas analysers provide electrolyte and metabolic data. In the author's institution, these values were not used clinically because of the risk of inaccuracy. To discover whether this approach was warranted, we compared values from our Radiometer point-of-care (POC) analyser and the laboratory. A total of 207 patients from an urban Emergency Department received venepuncture for sodium, potassium, creatinine and haemoglobin. Two samples were drawn; one analysed in the laboratory, the other on the POC machine. The results were: sodium: n=182, mean difference (MD) (lab-POC) 3.36, 95% limits of agreement (LOA) 0.18-6.54; potassium: n=171, MD 0.46, 95% LOA -0.12 to 1.03; creatinine: n=183, MD 1.6, 95% LOA -16.2 to 18.7; haemoglobin: n=191, MD -0.29, 95% LOA -1.71 to 1.12. Thus, sodium and potassium showed negative bias on the Radiometer compared with the laboratory. Creatinine and haemoglobin agreed well. We advocate the clinical use of POC values when taken in clinical context.