• R Comtois, S Bertrand, H Beauregard, and P Vinay.
• Département de médecine, hôpital Notre-Dame, Université de Montréal, Québec, Canada.
• Union Med Can. 1990 Nov 1; 119 (6): 317-21.

AbstractDehydrated patients usually present with an elevated serum urea level, owing in part to increased renal reabsorption of urea mediated by antidiuretic hormone (ADH). This study was carried out in order to examine whether, during dehydration, the variations in the serum urea level could discriminate patients with central diabetes insipidus (CDI) from those with dehydration due to other causes. We studied retrospectively 27 episodes of dehydration in 23 patients with CDI and 14 episodes in 14 patients without CDI. The mean serum urea level was 2.9 mmol/L in the CDI group and 15.4 mmol/L in the patients without CDI (p less than 0.001) while the mean serum sodium level was 155 mmol/L in both groups. During dehydration, patients with CDI decreased their serum urea level (4.0 +/- 2.3 vs 2.9 +/- 1.5 mmol/L, p less than 0.001). In addition, a positive correlation was found in the patients with CDI between the magnitude of diuresis and the percentage decrease in the serum urea level compared with the level before dehydration (r = 0.70, p less than 0.001). A striking increase in the clearance of urea (0.8 +/- 1 vs 2.1 +/- 1 ml/s, P less than 0.01), which exceeded the creatinine clearance (1.8 +/- 0.5 ml/s), was observed during dehydration in the six patients in whom clearance studies were done. Therefore, our results suggest that serum urea values can be used to distinguish patients dehydrated because of CDI from those with hypertonic dehydration but without ADH deficiency and that during dehydration the reabsorption of urea is mainly dependent on the renal action of ADH.

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