PURPOSE: We propose a criterion to clarify the underlying etiologies of nocturia. MATERIALS AND METHODS: Frequency-volume charts were recorded for 24 hours by 35 men and 32 women who were subjectively free of lower urinary tract symptoms and had no evidence of voiding disorders. At least 5 subjects were included in each of 5 age groups of 20 to 49, 50 to 59, 60 to 69, 70 to 79, 80 to 89 years for both genders. The charts were used to make a tentative criterion, which was validated in 39 elderly individuals with nocturnal frequency. RESULTS: Correlation and regression analyses indicated that the quotients of nocturnal urine output divided by body weight (U(N)/BW) and largest voided volume divided by body weight (V(L)/BW) were useful classification factors. Cutoffs, which were set close to worst quartiles, were 10 ml./kg. for U(N)/BW and 4 ml./kg. for V(L)/BW, respectively. Correction by body weight made the same criterion applicable irrespective of weight. Symptomatic elderly patients were classified into 3 mutually exclusive groups of nocturnal polyuria (U(N)/BW greater than 10 ml./kg.), low bladder capacity (V(L)/BW less than 4 ml./kg.) and combined nocturia. Of 20 subjects who voided 2 times a night 11 (55%) were classified as having nocturnal polyuria and 15 of 19 who voided 3 or 4 times (79%) were classified as having low bladder capacity or combined nocturia. CONCLUSIONS: The criterion provides a reasonable distinction of etiologies of nocturia, and may be usefulness in examination and treatment.
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