Relationship between plasma calcium fractions, other bone-related variables, and serum follicle-stimulating hormone levels in premenopausal, perimenopausal, and postmenopausal women.

The study comprises 186 untreated normal premenopausal, perimenopausal, and postmenopausal women in whom we measured serum follicle-stimulating hormone and a number of bone-related plasma and urinary variables. The calcium fractions in the plasma were calculated from the total calcium, albumin, globulin, anion gap, and bicarbonate concentrations. With a level of follicle-stimulating hormone within the reference range (up to 20 U/L) to define the premenopausal state, we confirmed previously reported menopausal rises in plasma calcium, phosphate, alkaline phosphatase, and bicarbonate, and in urinary calcium and hydroxyproline. However, inspection of the data, and t testing at different follicle-stimulating hormone criteria showed that these changes in bone-related variables did not generally occur until the level of follicle-stimulating hormone exceeded approximately 50 U/L. The plasma alkaline phosphatase level rose earlier than the other variables and was significantly elevated in subjects with follicle-stimulating hormone values above 30 U/L. The rise in plasma calcium was mainly a result of a rise in the ultrafiltrable fraction, which in turn was accounted for by rises in the ionized and complexed fractions, of which the complexed fraction was the most significant and proportionately the largest. The rise in the complexed fraction was accounted for by the increase in plasma bicarbonate.