The Journal of laboratory and clinical medicine
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The effect of changes in bicarbonate ion concentration on calcium ion concentration was examined in vitro in serum and protein-free solution. The findings in this study support the formation of a calcium-bicarbonate complex (CaHCO3+) that has a KA of 5.20 in protein-free solution. [Ca++] varied inversely with [HCO3-] in both serum and protein-free solution. This variation was independent of the known variation of [Ca++] with pH. ⋯ These findings indicate that abnormal bicarbonate concentrations should be considered when ionized calcium concentrations are estimated from total plasma calcium values in acid-base disorders. In metabolic acid-base disorders, the bicarbonate effect adds to the pH effect on calcium ion concentration. In compensated respiratory acid-base disorders, the bicarbonate effect subtracts from the pH effect on calcium ion concentration.