title: Accuracy diagrams: a novel way to illustrate uncertainty of estimated GFR.
abstract: Most studies that validate GFR equations present accuracy results stratified by measured GFR (mGFR; diagnostic correctness) or by estimated GFR (eGFR; diagnostic predictiveness) only, without a clear distinction in interpretation. The accuracy of a GFR equation is normally reported in percent (e.g. P30), but is often misinterpreted when stratified by eGFR. The aim of the study was to develop new accuracy measures and diagrams that allow straightforward interpretations and illustrations of the uncertainty in eGFR in clinical practice. We applied quantile regression to the distribution of estimation errors for two creatinine-based GFR equations, LM-REV and CKD-EPI, in a clinical cohort (n = 3495) referred for GFR measurement (plasma clearance of iohexol). Measures of bias and precision and accuracy intervals (AIs) were expressed in mL/min/1.73 m2. Diagrams with AIs were chosen as a novel way to present the error margin in eGFR at a pre-specified certainty level. It was shown that creatinine-based equations are still quite inaccurate in that large estimation errors could not be ruled out with satisfactory certainty. As an example, the 75% AI for the most accurate equation, LM-REV, was approximately ±10 mL/min/1.73 m2at eGFR = 45 mL/min/1.73 m2, whereas it ranged between -13 and +20 mL/min/1.73 m2at eGFR = 90 mL/min/1.73 m2. Accuracy intervals presented in diagrams can be used to illustrate the uncertainty of eGFR. Future validation studies should assess the variability in the predictiveness of eGFR across populations and clinical settings using tools and performance measures that are easy to interpret.
authors.affiliation: a Department of Laboratory Medicine , Lund University , Lund , Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Björk
authors.affiliation: a Department of Laboratory Medicine , Lund University , Lund , Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Grubb
authors.affiliation: b Department of Clinical Sciences , Lund University , Malmö , Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Sterner
authors.affiliation: a Department of Laboratory Medicine , Lund University , Lund , Sweden.
authors.forename: Sten-Erik
authors.initials: SE
authors.lastname: Bäck
authors.affiliation: c Department of Translational Medicine , Lund University , Malmö , Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Nyman
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D003287:Contrast Media / Q000493:pharmacokinetics; D003404:Creatinine / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012044:Regression Analysis; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology / Q000652:urine; D035501:Uncertainty
chemical_list: D003287:Contrast Media; D007472:Iohexol; D003404:Creatinine
keywords: Renal insufficiency; bias (epidemiology); clinical decision-making; predictive value of tests; reproducibility of results; statistical regression