Random Urinary Calcium/Creatinine Ratio in Dehydration and Hypercalcemic States

Background, Objective, and Hypothesis Dehydration is considered to be a rare etiology of hypercalcemia. In this study, we aimed to investigate the urinary calcium-to-creatinine ratio (urine Ca/Cr) in patients with dehydration-induced hypercalcemia and in patients with dehydration without hypercalcemia. Methods: A prospective cohort of 97 patients admitted to the internal medicine ward for dehydration and/or hypercalcemia in a tertiary medical center was included in our study. Data collected included basic demographics, comorbidities, serum and urine biochemistry, and endocrine investigations (25-hydroxyvitamin D and parathyroid hormone levels). Continuous variables were described by their average ± standard deviation and range. The variables were compared using non-parametric tests and the Chi-square test. We compared dehydrated patients with non-dehydrated patients and further compared patients with dehydration and hypercalcemia to patients with dehydration without hypercalcemia. Results: Overall, 97 patients were included in our analysis, of whom 38 (39.1%) were non-dehydrated, and 59 (60.8%) were dehydrated. The average level of albumin in blood was normal – 3.5 mg/dl in both dehydrated and non-dehydrated patients, but with a wider range and higher maximum value in dehydrated patients (3.5±1, 2-7.7 vs. 3.5±0.6, 2-4.6, p = 0.534). The urine Ca/Cr was significantly lower in the dehydrated patients in comparison to the non-dehydrated patients (0.4±0.5 mmol/mmol vs. 1.4±0.9 mmol/mmol, p< 0.001). Overall, 79 patients were hypercalcemic based on a cutoff of ionized calcium 1.2 mmol/l. Dehydration was considered the etiology of hypercalcemia in 36 (45.6%) patients. We analyzed the distribution and the mean of urine Ca/Cr by etiology in the hypercalcemic patients. Lower values of urine Ca/Cr were demonstrated again in the dehydrated patients. Patients with dehydration without hypercalcemia had the lowest urine Ca/Cr, compared with hypercalcemic patients with dehydration and without dehydration (0.1±0.1 vs. 0.5±0.6, and 1.4±0.9 p < 0.001). Using a cutoff of urine Ca/Cr < 0.2 to predict dehydration, the specificity was 100% and the sensitivity was 60.5%, with a positive predictive value of 100% and a negative predictive value of 64%. The ROC analysis demonstrated an area under the curve (AUC) of 0.802, which was statistically significant (p < 0.001). Discussion and Conclusion: Our study is the first comprehensive prospective cohort study designed to understand the relationship between urine calcium and dehydration. Hypocalciuria, defined by random urine Ca/Cr < 0.2 mmol/mmol, might predict dehydration. We demonstrated that the higher serum albumin in dehydration is not the only cause for the hypercalcemia. The very low urine Ca/Cr ratio in dehydrated patients without hypercalcemia strengthens our hypothesis that hypocalciuria might be an independent predictor of dehydration. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.