Correlação do clearance de creatinina e dos eletrólitos medidos na urina coletada em 12 e 24 horas em nefropatas

Abstract

Background: The clinical evaluation of renal function is an important part of prevention and monitoring of chronic kidney disease (CKD), for such, the assessment of creatinine clearance is still very used in health services practice and epidemiological studies, but its realization through the 24-hour urine collection proves impractical for active individuals. The overnight urine collection for 12 hours is an alternative that has been used in epidemiological studies in populations without known renal dysfunction. Objective: To validate the protocol for assessment of creatinine clearance and urinary excretion of electrolytes through the 12-hours night urine collection in people with CKD. Methods: 64 patients with CKD (19 - 88 years) collected urine for 24 hours in two bottles: day (7 am to 7 pm) and night (7 pm to 7 am at the day after). Blood collection took place in fasting for biochemical measurements. The correlation between variables was performed by Pearson test (r) and for concordance of measurements, the Bland-Altman. Results: Five patients were excluded due to collection error. Of the 59 subjects (31 men), 60% belonged to 2 and 3 CKD stages. The correlations between nocturnal urine and 24-hours were strong in relation to electrolytes (Na + r = 0.80, r = K + 0.80, Ca2 +, r = 0.86, p <0.001) and CrCl (r = 0,92; p <0.001). In 54 of 59 subjects the CrCl 12-hours-night was concordant with that of 24- hours. Conclusion: The nocturnal urine 12-hour collection provides CrCl and electrolytes excretion values similar to those obtained for 24-hours collection in subjects with renal impairment. Since this practical advantages to patients in an outpatient basis, it can be used in protocols for assessing renal function.