Urine Concentration Ability in Residents of CKDu Endemic Areas

Background The clinical presentation of chronic kidney disease of unknown origin (CKDu) is consistent with tubulointerstitial disease. Tests for tubular function, such as fasting urine osmolality, may be impaired in residents of endemic areas before GFR declines. This study describes fasting urine osmolality in individuals residing in areas endemic for CKDu who visited the All India Institute of Medical Sciences (AIIMS), Raipur. Materials and Methods This cross-sectional study was conducted at AIIMS, Raipur, Chhattisgarh, India, between June 2021 and May 2022. Adults >18 years, who had resided in endemic areas for at least 10 years, and were relatives of patients with CKDu admitted to the Department of Nephrology, were invited to participate in the study. Fasting urine osmolality was measured after 12 hours of overnight fasting, by the depression of freezing point method. An impaired urine concentration ability was defined as fasting urine osmolality <600 mOsm/kg. Results The study included 93 admitted relatives of 108 CKDu patients. The median age and eGFR of participants were 35 (IQR: 28, 46) years and 105 (IQR: 95, 116.5) mL/min/1.73m 2 , respectively. The median fasting plasma and urine osmolality were 290 mOsm/Kg (IQR: 286, 294) and 620 mOsm/kg H 2 O (IQR: 484, 850), respectively. Fasting urine osmolality was ≤600 mOsm/kg H 2 O in 46 patients (49.5%), 23 had (24.7%) values between 601 and 800 mOsm/kg H 2 O, and 24 (25.8%) had values >800 mOsm/kg H 2 O; 43 (46.2%) participants had hypokalemia, 15 (16.1%) had hyponatremia, and 14 (15.1%) had hypochloremia. Conclusion Almost 50% of seemingly healthy participants from the endemic CKDu belt visiting AIIMS Raipur have low mean fasting urine osmolality after 12-hour overnight water deprivation, suggesting a defect in concentrating ability.