title: How to best define patients with moderate chronic kidney disease.
abstract: BACKGROUND
  The objective of this study was to identify which formula may best identify moderate chronic kidney disease (CKD) (glomerular filtration rate (GFR) cut-off of 60 ml/min/1.73 m(2)).
  
  
  METHODS
  We compared the performances of 14 serum creatinine (S(cr)) and 11 cystatin C (Cys C) estimated GFR equations using inulin clearance (Cl(in)) as the reference test in a stable CKD population of 101 patients. Scatter, coefficient of variation, bias, precision, accuracy within 30% ranges from the reference method, agreements and receiving operating characteristics (ROC) of each test were compared.
  
  
  RESULTS
  ROC analysis identified Davis, Salzar, Virga and Cockcroft-Gault as the most sensitive (>or=85%) and the isotope dilution mass spectrometry (IDMS), Edwards, MacIsaac as the most specific (95%) to define the GFR cut-off level of 60 ml/min/1.73 m(2). Area under the ROC curve (AUC) was generally >0.8 (p <or= 0.0001). 2 x 2 contingency tables to define CKD demonstrated sensitivity of 90% for Davis, while the IDMS was the most specific (95%). Among the Cys-C-based equations, Filler was the most sensitive (83%) and MacIsaac was the most specific (95%).
  
  
  CONCLUSIONS
  The current equations lack consistent good performance to define CKD. The MDRD-IDMS equation missed 30% but demonstrated a high specificity to confirm those with moderate CKD. A combination of two equations, one sensitive and another specific, may be required for epidemiological studies.
authors.affiliation: Royal University Hospital, Department of Medicine, Division of Nephrology, University of Saskatchewan, Saskatoon, Canada.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Emara
authors.forename: Ahmed
authors.initials: A
authors.lastname: Zahran
authors.forename: Hassan
authors.initials: H
authors.lastname: Abd El Hady
authors.forename: Ahmed
authors.initials: A
authors.lastname: Shoker
mesh_terms: D000465:Algorithms; D003661:Decision Support Techniques; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000145:classification* / Q000175:diagnosis*; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity