Diurnal variation of urinary excretion for patients with psychosis, intermittent hyponatremia, and polydipsia (PIP syndrome).

Ten patients [8 men and 2 women, mean age (SD) 37.6 +/- 6.5 years] with psychosis, intermittent hyponatremia, and polydipsia (PIP syndrome) underwent serial determinations at 6:00 AM, 12 noon, 6:00 PM, and 12 midnight of levels of urinary creatinine concentration (UCR), urinary specific gravity (SPGR), and urinary osmolality (UOSM) on 8 consecutive Thursdays. Diurnal variation (p less than 0.015) was present in the case of each parameter of urinary excretion (UCR, SPGR, and UOSM). These three parameters remained very low throughout the day (mean UCR 19.0 mg/dl, mean SPGR 1.0033, and mean UOSM 112.6 mosmol/kg), which is consistent with severe and persistent hyposthenuria, and each parameter correlated well with the other two parameters (r between 0.78 and 0.93, p less than 0.001). The 6:00 PM (UC6PM) value for UCR correlated best with the daily mean UCR (UCM), providing the simple linear regression UCM = 0.7615 X UC6PM + 6.1503 (r = 0.912, p = 0.0005) for the 10 PIP patients. Twenty-four-hour urinary volume (24UV) could then be estimated using UCM and values of 17.5 and 12.5 mg creatinine/kg body weight for male and female PIP patients, respectively, to calculate the daily urinary excretion of urinary creatinine. The group mean 24UV was 6963 ml, with a range of 4934-9884 ml. We hope that information about the diurnal variation of urinary excretion (21.6%, 20.5%, 27.4%, and 30.4% of 24UV excreted in consecutive quartiles commencing with the 12 midnight to 6:00 AM quartile), coupled with the utilization of the equation UCM = 0.7615 X UC6PM + 6.1503 (r = 0.912, p = 0.0005) to estimate UCM as an index of 24UV in the PIP syndrome, will provide tools to better elucidate the relationship between psychosis and water dysregulation.