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eGFR in Chronic Kidney Disease: Guidelines and Limitations

This text provides information on the introduction of estimated glomerular filtration rate (eGFR) in diagnosing chronic kidney disease. It discusses the importance of reporting eGFR alongside serum creatinine (SCr), the choice of eGFR formula, and the limitations of the MDRD equation. It also highlights the role of clinical chemistry labs, diagnostic industry, and SKML in implementing eGFR. The text emphasizes the need for accurate creatinine measurement and performance requirements for eGFR estimation.

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eGFR in Chronic Kidney Disease: Guidelines and Limitations

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  1. eGFR introductie anno 2006 Take-home-messages Kreatinine Verklaard !? CM Cobbaert 14 september 2006

  2. Toenemende incidentie/prevalentie CNI Onderdiagnostiek en onderbehandeling sCr = ongevoelige marker voor detectie CNI ------------------------------------------------------------------ Richtlijnen: rapporteer eGFR naast SCr! Keuze eGFR formule anno 2006: kritisch! Betrouwbare eGFR mits adequate assay/standaardisatie SCr ------------------------------------------------------------------ Rol klinisch chemische labs, diagnostica industrie en SKML! Chronische nierinsufficientie

  3. Introductie I. Lab issues: choices have to be made!

  4. GFR estimation Perc e nt of es tim ate s within 30 % of th e m eas ur e d G FR in th e M DRD Study va lid a tion sa m pl e (n = 558 ). 10 0 GFR estimate 8 0 Creat clearance estimate 6 0 4 0 2 0 0 Coc kroft- 2 4-H o ur Cockro ft - 24 -H ou r Rec i p r oca l M D RD 6 M DRD 4 Re c i p r oca l G au l t C r e at i n i n e G au l t [ C] C reat i n i n e SC r SC r [C] Pa rameter Pa rameter C l eara n ce C l earance [ C] Redr a wn from: K/ D OQI Cli n ical pra c tic e gui d eli n es for chronic kidne y disease. Am J Kidne y Di s 20 0 2; 3 9: S 1-S 2 66.

  5. NKDEP recommends the MDRD four parameter estimation equation for adults age 18 and older GFR (mL/min/1.73 m ) = 2 186 x creat serum / 88.4 (µmol/L) * -1.154 x Age -0.203 x 0.742 (If Female) x 1.210 (If African-American) * u se 186 for CONVENTIONAL calibration; * u se 175 for calibration TRACEABLE TO IDMS

  6. 4P-MDRD equation limitations Applicable in adult (18-70 years) whites and • African-Americans with chronic GFR <90 mL/min/1.73 m 2 Acceptable performance for diabetics  Agreement with measured GFR is poorer for: • Hospital inpatients  Acute renal failure  Normal renal function  Validation is underway for additional ethnic • groups, patient groups, and individuals with normal renal function

  7. Creatinine measurement limitations affecting the 4 P-MDRD Conventional calibration has not been • standardized among methods Original MDRD equation was based on Beckman CX3  routine method results from Cleveland Clinic Jaffe method non-specificity influences on • individual patient creatinine results Measurement bias and imprecision have a larger • impact on result variability as creatinine values get lower (GFR gets higher)

  8. Impact of creatinine bias on GFR Bias, mol/L 14 0 - 5 -8 mL/min = -12% error 0 12 0 5 -17 mL/min = -27% error 10 0 11 8 0 27 6 0 4 0 2 0 Large effects > 60 0 0 20 40 60 80 1 0 0 12 0 2 eGFR without bias in serum c r e a tinine, mL/min/1.73 m M y ers et al. Cli n Che m 2006;52:5-18

  9. Impact of imprecision on GFR 160 95% Confidence Interva l for eGFR 140 at creatinine = 88.4 mol/L (1 mg/dL) 53-70 mL/min/1.73 m at SD = 5.3 mol/L 120 2 46-85 mL/min/1.73 m at SD = 11.5 mol/L 2 100 80 60 40 20 0 88.4 µmol/L 0. 0 1 . 0 2. 0 3 . 0 4.0 Creatinine, mg/dL M y ers et al. Cli n Che m 2006;52:5-18

  10. What creatinine method performance is needed? Total error in creatinine measurement is not to increase the variability in eGF R more than 10% in the critical creatinine range 1.0-1.5 mg/dL (88-133 μ mol/L) Comparable performance is needed in the 0.6-  1.0 mg/dL ( 53-88 μ mol/L) range for pediatric patients and to extend eGF R to higher values Method non-specificity also needs to be  addressed

  11. Total Error budget for creatinine measurement in the range 88-133 µmol/L M y ers et al. Cli n Che m 2006;52:5-18

  12. Implement 4 P-MDRD now!! Use the conventional calibration 4P-MDRD eq. • for methods not calibrated to IDMS Many routine methods have a calibration bias that is  similar to that of the routine method used in the MDRD study. Use the IDMS-traceable 4P-MDRD equation for • methods calibrated to IDMS Use creatinine reported to two decimals (mg/dL), • or nearest whole number (µmol/L), in the MDRD calculation

  13. Reporting 4 P - MDRD Report GFR selectively (metabolic stable pts) • (Consider if appropriate for inpatients) Report two values? • GFR if African-American Caucasian  est If value is 60, report rounded to a whole • ≤ number (e.g. 53 mL/min/1.73 m ) 2 If value is > 60, report as “>60 mL/min/1.73 m ” • 2 Limited by calibration variability, imprecision, and MDRD equation accuracy

  14. Clinical issues to communicate Creatinine reference interval change • Creatinine clearance change if urine and serum  calibrations are affected differently IDMS-calibrated creatinine results will affect • decision algorithms used to adjust drug doses Cockcroft-Gaul t estimation or creatinine clearance is  commonly used by pharmacists (mfr. claims) Criteria based only on seru m creatinine concentration  Pediatrics: recommend a measured GFR or creatinine  clearance for critical and potentially toxic drug effects

  15. Effect of ≠ equations on eGFR eGFR Serum creatinine is measured with an IDMS-traceable enzymatic method (Roche); N = 375 Serum creatinine (mol/L)

  16. eGFR regression: Cockroft-Gault versus 4 parameter IDMS_MDRD Creatinine clearance estimate Amphia database; N = 375 eGFR estimates are derived from enzymatic serum creatinine (Roche) GFR estimate

  17. II. IVD manufacturerissues - Creatinine standardization programme Eliminate the bias between different methods • Make calibration traceable to IDMS reference  measurement procedure (gold standard) Improve the accuracy and consistency of • estimated GFR • Creatinine results for most methods will be10- 20% lower after standardization IVD manufacturers expect two years to • implement recalibration of existing methods

  18. Calibration Traceability - Routine Serum Creatinine Methods 1˚ Calibrator NIST SRM 914a 1˚ RMP GC-IDMS & LC-IDMS 2˚ Reference Materials NIST SRM 967 MFR Selected Method Product Calibrators Routine Method Clinical Sample Result

  19. III. SKML issues Accommodate grading of results from • participants during the transition from conventional to IDMS-traceable calibration A bimodal distribution of results may occur  Communicate with IVD manufacturers regarding • timing of calibration standardization Introduce programs that use commutable serum • materials and evaluate eGFR performance

  20. Survey 2006.1 Creatinine, sample: C EQA-material is commutable since January 2005

  21. Desirableimprecision Introductie CNS CNS: Combi Nieuwe Stijl (commuteerbaar EQA-materiaal; waardetoekenning met referentiemethode)

  22. Effect of IVD/98/79 EC implementation and introduction of commutable EQA-materials on mean absolute bias (MAB) in the Netherlands % MAB Desirable bias

  23. EQA provider / SKML chemistry section: post-market vigilance of analytical performance tools:trueness controls Clinical chemist in case of excessive bias: temporary (re)calibration tools:secondary reference materials < SKML CLUE = commutability Monitoring sCr std. efforts Manufacturer& directive 98/79/ECon IVD-MD & JCTLMTraceability chain

  24. Summary Report eGFR with creatinine results using the • correct 4P-MDRD equation. Limitations! Coordinate use of a creatinine method with • IDMS-traceable calibration with use of the IDMS- traceable MDRD equation. Transition! Communicate the clinical issues associated • with IDMS-traceable creatinine results.

  25. Dr. C.W. (Cas) Weykamp Streekziekenhuis Kon. Beatrix WINTERSWIJK Dr. H. (Henk) Baadenhuijsen UMC St Radboud NIJMEGEN Dr. P.F.H. (Paul) Franck Ziekenhuis Leyenburg DEN HAAG Dr. ir. A.W.H.M. (Aldy) Kuypers Maasziekenhuis Pantein BOXMEER Dr. M.H.M. (Marc) Thelen Sint Annaziekenhuis GELDROP Dr. Ch.M. (Christa) Boersma-Cobbaert Amphia Ziekenhuis BREDA Adviseurs: Herman Steigstra & Wim De Jongh SKML - Chemistry Section

  26. Kreatinine Verklaard !? ALL THINGS ARE READY IF OUR MINDS BE SO William Shakespeare HenryV Thanks!

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