Plasma concentrations of parathyroid hormone-related protein (PTHrP), parathyroid hormone, alkaline phosphatase, osteocalcin and albumin-adjusted calcium were measured along with nephrogenous cyclic adenosine monophosphate (NcAMP) in 10 normal women longitudinally through pregnancy. In addition, an assessment of bone resorption was made in these same subjects by the measurement in true fasting urine specimens of the calcium/creatinine ratio (Ca/Cr), hydroxyproline/creatinine ratio (HP/Cr), pyridinoline/creatinine ratio (Pyr/Cr) and deoxypyridinoline/creatine ratio (Dpyr/Cr). The PTHrP level rose through pregnancy from (mean +/- SEM) 0.8 +/- 0.2 pmol/l in the first trimester to 2.7 +/- 0.2 pmol/l 6 weeks postpartum (p < 0.0001). Serum alkaline phosphatase rose from 94 +/- 8 U/l (first trimester) to 347 +/- 25 U/l at term (p < 0.0001). A significant positive correlation was evident between PTHrP and alkaline phosphatase up to term (r = 0.44, p < 0.005). Parathyroid hormone concentrations remained unchanged during pregnancy but rose significantly postpartum from 1.8 +/- 0.2 pmol/l (first trimester) to 3.1 +/- 0.5 pmol/l (p < 0.0001). Similarly, osteocalcin, a marker of bone formative activity, remained unchanged through pregnancy but rose significantly at 6 weeks after delivery to 0.38 +/- 0.05 nmol/l from 0.19 +/- 0.03 nmol/l (first trimester) (p = 0.019). No significant change was noted in serum-adjusted calcium or NcAMP, either through pregnancy or at the postpartum assessment. Fasting urinary Ca/Cr fell through pregnancy from 0.70 +/- 0.11 (first trimester) to a nadir of 0.19 +/- 0.04 6 weeks postpartum (p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)
SUMMARY The algorithms used in this hospital to assess calcium status are calculated ionised serum calcium and the serum calcium concentration adjusted for albumin. In order to establish their clinical usefulness, they were compared with the ionised calcium concentration measured on the Nova 2 instrument in patients with various calcium and protein abnormalities. Good correlation was found between the measured and calculated values. The predictive values for the calculated results and for total serum calcium concentrations are presented. In this series, the derived values were useful in predicting the serum ionised calcium concentration of the patients studied.
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