PATHOPHYSIOLOGY OF HYPOCALCIURIA IN PREECLAMPSIA - MEASUREMENT OF INTESTINAL CALCIUM-ABSORPTION

Objective: To analyze calcium absorption using stable isotopes in pati ents with preeclampsia and in normotensive controls. Methods: Fifteen pregnant subjects were studied: eight with preeclampsia (hypertension and proteinuria) and seven normotensive controls. All patients were in gesting their normal diet. The subjects received two stable calcium is otopic tracers. An oral tracer (Ca-44, 0.0124 mmol/kg) was given with milk, while an intravenous tracer (Ca-42, 0.00249 mmol/kg) was infused over 7-10 minutes. Calcium concentration was determined by atomic abs orption spectrophotometry, and isotope ratios by thermal ionization ma ss spectrometry from pooled 24-hour urine samples. Results: No differe nce was noted in fractional intestinal absorption between preeclamptic subjects (0.282 +/- 0.051) and normotensive controls (0.306 +/- 0.079 ) (P = .49). However, the fraction of dietary calcium appearing in the urine differed significantly (0.06 for preeclamptic subjects and 0.08 7 for normotensive controls; P = .008). Conclusions: Despite the indir ect evidence of others, calcium absorption does not appear to be impai red in patients with preeclampsia. The retention site of the unexcrete d calcium is unidentified.