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ANALYTICAL AND CLINICAL EFFECTS OF CREATININE STANDARDISATION

ANALYTICAL AND CLINICAL EFFECTS OF CREATININE STANDARDISATION. Prof. J. Delanghe, MD, PhD Dept. Clinical Chemistry Ghent University. Creatinine according to Jaffe…. Analysis following deproteinisation pseudochromogens  time window Lloyds’s reagent optimalisation extremely cheap.

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ANALYTICAL AND CLINICAL EFFECTS OF CREATININE STANDARDISATION

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  1. ANALYTICAL AND CLINICAL EFFECTS OF CREATININE STANDARDISATION • Prof. J. Delanghe, MD, PhD • Dept. Clinical Chemistry • Ghent University

  2. Creatinine according to Jaffe…. • Analysis following deproteinisation • pseudochromogens  time window • Lloyds’s reagent • optimalisation • extremely cheap

  3. Jaffe reaction

  4. VARIATION BETWEEN METHOD-GROUPS

  5. Variability in Jaffé’s method (I)(Hanser et al, Ann Biol Clin 2001;59:737-42)

  6. Technical evolution • 1954 Skeggs: dialysis membrane • 1970 centrifugal analyzer→ no longer dialysis step!→ protein error introduced • 1980 random acess analyzer

  7. The protein error got into the determination! • 1970 - 2000: Jaffé rules the creatinine market in Europe and VS • Protein error leads to underestimation of GFR! (CrCl << GFR) • some enzymatical determinations recalculated to Jaffé-equivalence!

  8. What happened with creatinine? • Protein error got into the determination! • Only ref. values were adapted!!!! • Physiology books, derived formulas, • pharmacokinetics??????

  9. Pseudochromogens • Enzymatic methods theoretically eliminate effect of pseudochromogens • Not widely used (cost price)

  10. Creatinine clearance • urine collection often difficult in practice • Intra individual CV 10 % • practical formulas: • e.g. Cockroft & Gault Nephron 1976;16:31-41

  11. COCKROFT & GAULT Cl = (140 -L) (year) x W(kg) S (mg/dl) x 72 for women  result x 0.85 MDRD (classical) GFR (mL/min/1.73 m2) = 186 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American) SCHWARTZ practical in children and infants GFR (ml/min/1.73 m2) = 0.55 x L (cm)/P (mg/dl) (Pediatrics 1976; 58:259)

  12. 7.12.2003 CE GUIDELINES • CE Guideline 98/79/EG on in-vitro diagnostics • PROBLEMS: • Calibration using standard of “higher order” • link with literature? • What with derived calculations?

  13. REALITY AND THEORY IN DISAGREEMENT!

  14. Creatinine in children

  15. CREATININE IN CHILDREN

  16. Clinical impact of a change in CrCl, reference range • Fields of potential risk • drugs eliminated by renal excretionaminoglycosides/glycopeptides/carboplatine • Important for borderline Clcr for antibiotics • management for some antineoplastic agents • for clinical trials

  17. LOOKING INTO THE FUTURE

  18. Cystatin C vs. creatinine • Advantages: • 1/[Cys C] ~ GFR • independent from muscle mass, diet • urinary determination not needed • valuable in the “blind range” zone of creatinine

  19. NIST SRM 967 • Commutable reference material • Submitted bij JCTML • IDMS • 0.8 mg/dl • 4 mg/dl • Revised MDRD • Release postponed!!

  20. PREPARATION OF SRM 967 CREATININE IN HUMAN SERUM • Prepared at Solomon Park Research Institute, Kirkland, Washington • Human serum with the following characteristics: • Master Pool comprised of units drawn from postmenopausal female donors • to yield pool with creatinine of 0.8 mg/dL or lower. • Collected and handled following NCCLS C37-A • All units tested and found negative for viral markers • Pooled and split into 2 sub-pools: • Low level, High level, second sub-pool spiked with crystalline creatinine • to bring the concentration to 4.0 mg/dL. • LC/MS METHOD FOR SERUM CREATININE • [P. Stokes, G. O’Connor, J Chromatog B 794, 125-136 (2003)] • Spike serum with creatinine-d3, Precipitate proteins with cold ethanol, Centrifuge, Decant supernatant and dry under nitrogen • Reconstitute in water and filter, Dilute with 10 mM NH4 acetate • LC/MS • Phenomenex LUNA C-18; Gradient: 10 mM NH4 acetate for 7 min, • Then acetonitrile:10 mM NH4 acetate (80:20) and hold for 13 min • Electrospray ionization – positive mode monitoring (M+H)+ at 114/117 • Calibration from standard curve using SRM 914a and creatinine- d3

  21. NIST SRM 967 • 2006-2009:Adaptation by IVD industry • 2010: problem solved? • In the mean time MDRD is pushing!!!! • Risks for confusion !

  22. Some Statistics (United States) • End-stage renal disease (ESRD) • Prevalence (2003): 452,957 U.S. residents were under treatment  • Resulting from these primary diseases: • Diabetes: 165,113Hypertension: 109,642Glomerulonephritis: 74,444Cystic kidney: 20,409All other: 83,349 • Number of kidney transplants performed • 2003:  16,0432000:  14,5571995:  12,0211990:  10,0121988:  7,501

  23. MDRD: THE SOLUTION?? • Limitations (age, CrCl value, ethnicity,..) • Confusion still ungoing • “Some unwanted side effects” • Drug dosage schemes! • Pediatrics?

  24. Conventional Calibration MDRD Equation • This equation should be used only with those creatinine methods that have not been recalibrated to be traceable to IDMS. If you have any question about the traceability of the calibration for the method, NKDEP recommends that you contact the reagent and/or calibrator manufacturer for assistance. • The equation requires 4 variables: • Serum, or plasma, creatinine (Scr) • Age in years (18 years or older) • Sex • Race (African American or not) • When Scr is in mg/dL (conventional units):GFR (mL/min/1.73 m2) = 186 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American)

  25. CONFUSION…… • Conventional Calibration MDRD Equation • should be used only with those creatinine methods that have not been recalibrated to be traceable to IDMS. For more information, visit NKDEP's Laboratory Professionals section. • GFR (mL/min/1.73 m2) = 186 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American) (conventional units) • IDMS-Traceable MDRD Equation • should be used only with those creatinine methods that have been recalibrated to be traceable to IDMS. For more information, visit NKDEP's Laboratory Professionals section. • GFR (mL/min/1.73 m2) = 175 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American) (conventional units)

  26. IDMS-Traceable MDRD Equation • This equation should be used only with those creatinine methods that have been calibrated to be traceable to IDMS. If you have any question about the traceability of the calibration for the creatinine method, NKDEP recommends that you contact the reagent and/or calibrator manufacturer for assistance. • The equation requires 4 variables: • Serum, or plasma, creatinine (Scr) • Age in years (18 years or older) • Sex • Race (African American or not) • When Scr is in mg/dL (conventional units):GFR (mL/min/1.73 m2) = 175 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American)

  27. Conclusions (I) • Compensated Jaffé method results in a more correct approximation of GFR • Cockroft & Gault, MDRD : only valid for enzymatic or “compensated” methods • Schwartz formula not usable for compensated (or enzymatic) method!!! • Adaptation of reference values is insufficient !!!!!

  28. CONCLUSIONS (II) • Careful when using nomograms for drug dosage! • Creatinine standardisation: situation is still confuse! Vigilance necessary • MDRD has limitations (CrCl value, age, standardisation) which should be respected • Task for industry, laboratories, clinicians, pharmacists

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