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

Abstract

Background: The evaluation of the renal function and of the factors of cardiovascular risk through the electrolytes and creatinine excreted in the urine, it has been difficult, so much in practice clinic as well as in epidemiological studies for the fact of the reference patterns have been established with sample of urinary collected in 24 hours, wich hinders the calculation of the creatinine clearance (CrCl), that is important in the follow up of hypertense people, diabetics and other chronic and acute diseases attendance. Objective: To compare the relationship that exists on the measure parameters of the renal function between of the daylight, nocturne and 24 hours urinary excretion using the creatinine and electrolytes, by the analysis of the urinary volume and of the data laboratory; Methodology: It was studied a sample of 91 participants with age understood among 34 to 64 years. The participants were verbal and writing instructed on how to proceed during the collection of the urine produced in the 24 hours, fractioned in two periods of 12 hours (of the day: 07 AM - 19 PM and nocturne: 19PM – 07AM). The creatinine, Na+ , K+ and Ca++ concentrations in each volume was measured. The blood was collected by venopuntion in fasting of 12 hours for biochemical measures. Blood pressure, anthropometry and rest ECG were also measured. The results are presented as mean ± standard deviation and compared through the student t test for independent samples. Statistics significance whenever P <0,05. Results: The average of age of the sample was 47±7,8 years, the body mass index (BMI) ≥26,9±4,1 kg/m2 and body surface of 1,75±0,16 m2 . The smokers prevalence was 17,6%, dyslipidemia (total cholesterol ≥200mg/dL and/or HDL ≤45mg/dL) of 60,4%, hypertension of 31,9% and obesity (BMI ≥30kg/m2 ) of 19,8%. All the sample had serum creatinine <1,3mg/dL. The daylight and nocturne urinary volumes were similar (1,09±0,54 vs 1,10±0,49 L; P>0,05), as well as the excretion of Ca++ (68,8±48,9 vs 73,1±62,1mg; P>0,05) and the creatinine (643,9±231,3 vs 591,0±208,4mg; P>0,05). The Na+ (115,2±42,9 vs 99,8±43,6 mEq; P <0,05) and K + (35,7±12,4 vs 22,3±10,1mEq; P <0.001) excretion were larger during the daylight. ClCr was different in the two periods (92,5±27,4 vs 84,0±23,7ml.min1 /1,73m2 ; P <0,05), but with high correlation degree between the daylight and nocturne value and the corresponding value to the 24 h period (r=0,89; P <0,000 and r=0,85; P <0,000 respectively). Conclusion: The glomerular filtration rate measured by endogenous CrCl and the urinary excretion of electrolytes (Na+ , K+ and Ca++) can be estimated in urine sample collected in 12 hours, particularly at night, facilitating the obtainment of these data on great epidemic studies.