Biological Variation of Blood Acid-Base Status: Consequences for Analytical Goal-Setting and Interpretation of Results

Analytical, intra-individual, and interindividual components of variation have been determined for pH, pco2, bicarbonate, base excess, and total CO2 in capillary specimens of whole blood from a cohort of 14 healthy subjects. Calculated analyticalgoals (SD) are pH O.008, p2 ‘cO.9 mmHg, bicarbonatecO.5 mmol/L, base excess cO.5 mmol/L, and totalCO2 0.5 mmol/L. Because pH and base excess vary littleb tween individuals, population-based reference values forthem willbe of utilityin interpretationf results;pco2, bicarbonate, and total CO2 show more marked variation between individuals, and reference values for them will be of more limited use. The generally applicabledifferences re-quired for two results to be significantly different (P 0.05) when goals are met-which is currently feasible-are pH: 0.04, o2: 0.745 kPa (5.6 mmHg), bicarbonate: 2.6 mmol/L