Urine concentration in elderly women and men

Background: Concentrated urine reflects high degree of renal fluid conservation, which is of relevance to healthcare. Middle-aged women have less concentrated urine than men. The present observational study evaluated whether this difference remains in elderly hospital patients and in acute medical conditions. Methods: Urine sampling was performed in 1,316 subjects for analysis of urine-specific gravity, osmolality, creatinine, and color. Patients were recruited from three hospital settings (median age, 78 years), while 27% of the subjects were healthy controls (median age, 43 years). Results: Biomarker values were significantly higher in men than in women in all settings, indicating less intense renal water conservation in women. Statistically significant sex differences were found in 354 healthy volunteers, in 286 patients who delivered a urine sample just before surgery, in 311 patients seeking acute care, and in 360 patients who underwent in-hospital geriatric care. The average difference was 6% for urine-specific weight, 14% for osmolality, 25% for creatinine, and 19% for urine color. The biomarker values decreased with age and with the occurrence of albuminuria. Female sex was independently associated with significantly lower values of all four biomarkers, whereas age and albuminuria showed mixed results. More dilute urine was found in patients seeking medical attention for heart conditions, including angina pectoris and heart failure. Conclusion: Women in the hospital setting have less concentrated urine than men even after correction for age and albuminuria.