title: Correlation between the creatinine clearance in the urine collected during 24 hours and 12 hours.
abstract: BACKGROUND
  Creatinine concentration in plasma has been used to evaluate renal function. However, the endogenous creatinine clearance (CrCl) is more sensitive to this goal.
  
  
  OBJECTIVE
  Correlate the CrCl calculated from urinary collects of 12 h and 24 h.
  
  
  METHODS
  Ninety five volunteers (34-64 y) collected the urine for 24 h into two bottles: night, from 7 am to 7 pm and day, from 6 am to 7 pm. A fasting blood sample was used to measure plasma creatinine. Correlation between variables was determined by Pearson method (r) and the agreement between night and 24 h CrCl was determined by the Bland-Altman plot.
  
  
  RESULTS
  Urines of 4 individuals were discarded because of collect errors. In the final sample (n = 91; 42 males), hypertension was found in 23 and diabetic in 5. The CrCl (mL/min/1.73 m²) was slightly lower in females in the night (77.8 ± 22.7 versus 88.4 ± 23.6; p < 0.05) and similar in males (91.2 ± 22.9 versus 97.3 ± 30.9; p > 0.05). Strong correlations were observed between the CrCl calculated from the night and day urines and the 24 h (r = 0.85 and 0.83; respectively). Agreement between the CrCl calculated from night or day urine and the 24 h urine was observed, respectively, to 85 and 83 individuals.
  
  
  CONCLUSIONS
  The 12 h urine, mainly obtained at night, gives CrCl values similar to those obtained in the 24 h collect. Since urine collect is easier to outpatients at night, this period should be chosen in the clinical evaluation of the glomerular filtration rate.
authors.affiliation: Department of Physiological Sciences – Center of Health Sciences (CCS)– Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Amilcar Bernardo Tomé
authors.initials: AB
authors.lastname: da Silva
authors.forename: Maria del Carmen Bisi
authors.initials: Mdel C
authors.lastname: Molina
authors.forename: Sérgio Lamêgo
authors.initials: SL
authors.lastname: Rodrigues
authors.forename: Enildo Broetto
authors.initials: EB
authors.lastname: Pimentel
authors.forename: Marcelo Perim
authors.initials: MP
authors.lastname: Baldo
authors.forename: José Geraldo
authors.initials: JG
authors.lastname: Mill
mesh_terms: D000328:Adult; D003404:Creatinine / Q000652:urine*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors
chemical_list: D003404:Creatinine