Hypocalciuria of preeclampsia is independent of parathyroid hormone level

Hypocalciuria is a feature of preeclampsia. The roles of parathyroid hormone (PTH) and vitamin D 1,25(OH)₂D₃ (calcitriol) in its pathogenesis have not yet been determined. Fourteen preeclamptic women were compared with 12 women with chronic hypertension and 11 normotensives, all in the third trimester. Preeclamptics had the lowest urinary calcium excretion rate (62.1 ± 32.8 mg/24 hours) compared with chronic hypertensive women (162.6 ± 97.8 mg/24 hours) and normotensive controls (225.6 = 146.9 mg/24 hours) (P < .05). Serum PTH was lowest in preeclamptics (9.8 ± 5.5 pg/mL), in contrast to the chronic hypertensives (18.5 ± 2.7 pg/mL) and normotensives (16.4 ± 3.2 pg/mL) (P < .005). Similarly, urinary cyclic adenosine monophosphate (cAMP) excretion was 2.9 ± 1.4 μmol/24 hours in the preeclamptics, 5.1 ± 1.7 μmol/24 hours in the chronic hypertensives, and 4.6 ± 1.3 μmol/24 hours in the normotensive group (P < .05). These data suggest that the mechanism of hypocalciuria in preeclampsia is independent of the PTH-calcitriol axis. Therefore, it is suggested that the hypocalciuria of preeclampsia is due to intrinsic renal tubular dysfunction.