Hypocalciuria in pre-eclampsia and gestational hypertension due to decreased fractional excretion of calcium

Introduction: This study investigated whether reduction in urinary calcium excretion is due to decreased fractional excretion of calcium, and evaluated the potential of urinary calcium to creatinine ratio as a screening test for pre-eclampsia.
Material and methods: This prospective study involves 83 pregnant subjects: 29 with pre-eclampsia, 27 with chronic hypertension and 27 normotensive pregnant controls. Serial blood and urine specimens were obtained and analyzed in the third trimester (32 weeks to term).
Results: The serum levels of calcium, phosphate, urea and uric acid were not different among the groups. In contrast, the serum albumin was significantly reduced in pre-eclamptic women and chronic hypertensive women, compared with normotensive pregnant controls. Pre-eclamptic women had the lowest urinary calcium excretion rate (1.70 ±0.26 mmol/day) compared with chronic hypertensive women (4.23 ±0.59 mmol/day, p < 0.05) and normotensive pregnant women (4.43 ±0.60 mmol/day, p < 0.05). Hypocalciuria in pre-eclamptic women was associated with decreased fractional excretion of calcium of 1.45 ±0.05 mmol/day compared with 4.02 ±0.09 mmol/day in normotensive women (p < 0.05). There was decreased urinary calcium to creatinine ratio (0.17 ±0.03 mmol/mmol) in pre-eclamptic women compared with normotensive women (0.45 ±0.08 mmol/mmol, p < 0.05).
Conclusions: These findings suggest that hypocalciuria in pre-eclampsia is associated with decreased fractional excretion of calcium, suggesting a mechanism which may involve increased tubular reabsorption of calcium. Urinary calcium to creatinine ratio may be a useful potential screening test for pre-eclampsia.