Increase in plasma lactate at the menopause and its relation to the "anion gap".

The mean plasma anion gap (Na + K + Ca + Mg)--(Cl + HCO3(-) + HPO4(2-) + protein), was significantly higher in post-menopausal women compared with pre-menopausal women (8.04 mEq/l compared with 7.03 mEq/l). This change was due, in part, to an increase in the plasma lactate concentration and to smaller increases in citrate and pyruvate concentrations. There were also changes in bicarbonate and chloride concentrations which suggested an increase pH of approximately 0.02 U. Together, these changes accounted for 46% of the increase in the "anion gap", leaving 54% unexplained. It is suggested that the rise in plasma lactate concentration may be due to mild alkalosis and that this change may account for the rise in plasma urate concentration which also occurs at the menopause.