1. Serum Creatinine and eGFR Where Are We Now? Dr Mike Bosomworth Lead Clinician - Blood Sciences Leeds Teaching Hospitals 16 th April 2013 1

2. 2 Why measure serum creatinine?

3. 3 RENAL CLEARANCE Substance cleared by renal excretion clearance (Cy ):- Cy = UyV Py (V = Urine flow rate) Substance freely filtered and excreted by glomerular filtration (i.e. not secreted) renal excretion determined by GFR and plasma concentration:- UyV = GFR x Py then GFR = UyV = Cy Py

4. Does Creatinine Clearance = Glomerular Filtration Rate? Is creatinine excreted by glomerular filtration alone (renal clearance = GFR)? Is creatinine filtered and secreted (renal clearance exceeds GFR)? Is creatinine filtered and reabsorbed (renal clearance less than GFR) 4

5. 5 Equations for GFR Calculation Recommended equation ID-MS traceable abbrMDRD (Scr in umol/l) eGFR = 175 x (((Scr – intercept)/slope)x 0.011312) -1.154 x Age -0.203 x (0.742 if female) x (1.21 if African ) N.B. Most recent Schwartz Formula uses constant of 0.41 (IDMS calibrated enzymatic assay) CKD-EPI ?

6. 6 Jaffe Reaction Creatinine + picric acid Orange-red (Janovski) complex Read @ 510 nm alkaline pH

7. 7 Assay Interferences Jaffe Bilirubin (negative) Keto Acids Glucose and other metabolites Proteins Drugs

8. 8 RENAL CLEARANCE Substance cleared by renal excretion clearance (Cy ):- Cy = UyV Py (V = Urine flow rate) Substance freely filtered and excreted by glomerular filtration (i.e. not secreted) renal excretion determined by GFR and plasma concentration:- UyV = GFR x Py then GFR = UyV = Cy Py

9. Jaffé Reaction - Modifications Kinetic – Interference Rapid – e.g. acetoacetate – within 20 secs Slow – e.g. protein – 80 – 100 secs Measure absorbance change between 20 and 80 secs Compensated – Interference Protein – adjust calibrator set point to take account of pseudo-creatinine contribution of protein i.e. subtract approx 27 umol/l Combination of the above 9

10. Jaffé Reaction – Modifications O’Leary + Kinetic 10

11. Enzymatic Creatinine One Method? 11

12. 12 Assay Interferences Jaffe Bilirubin Keto Acids Glucose and other metabolites Proteins Drugs Enzymatic Drugs (fewer)

13. 13

14. 14 Jaffe M: Ueber den Neiderschlag, welchen Pikrinsaeure on normalen Harn erzeught and ueber eine neue Reaktion des Kretinins Z.Physiol.Che. 1886 ;10:391-400

15. 15 C.V. = 6.0% C.V. = 12.4% Clinical Chemistry 52:15–18 (2006)

16. 16 Clinical Chemistry 52:15–18 (2006)

17. Recommendations for Improving Serum Creatinine Measurement: A Report from the Laboratory Working Group of the National Kidney Disease Education Program – Clin Chem 2006;52:5-18 IVD manufacturers should recalibrate serum creatinine methods to be traceable to IDMS and should coordinate the introduction of recalibrated serum creatinine methods with the introduction of a revised GFR-estimating equation appropriate for use with zero-biased routine method 17

18. Certification of Creatinine in a Human Serum Reference Material by GC-MS and LC-MS Clin Chem 2007;53:1694-1699 SRM 967 - 66.5 umol/L for serum pool 1 (a value close to the diagnostically important concentration of 88.4 umol/L) and 346.2 umol/L for serum pool 2 (a concentration corresponding to that expected in a patient with chronic kidney disease). 18

19. 19 WEQAS Creatinine Scheme Total no. Participants: 390

20. 20 Method Bias Relative to Overall Mean (Distributions KG – KM)

21. Regional Oncology Unit 21

22. 10 miles 22

23. Theoretical Differences using NEQAS Slopes and Intercepts (2010) Female, 45y, 55kgFemale, 75y, 60kg UK labs Creatinine 2 ( μ mol/l) C&G 3 (ml/min) Carboplatin 4 (mg) C&G 3 (ml/min) Carboplatin 4 (mg) Enzymatic5%50108.580181.0636 Kinetic Jaffe - Abbott10%6090.769467.7556 Kinetic Jaffe - Bayer4%6485.166163.5531 Kinetic Jaffe - Dade Behring2%5893.771269.9569 Kinetic Jaffe - Olympus12%6485.466363.8533 Kinetic Jaffe - Compensated47%6090.869567.8557 O'Leary7%6781.263760.6514 Endpoint Jaffe2%6880.863560.3512 Standardized Creatinine 1 50109.280581.5639 Variability 34% 26%34%24% 23

24. 6 Jaffé and 3 Enzymatic West Yorks (10 samples) 24

25. Calculated Clearance / GFR vs Measured 25

26. Calculated vs Measured C-G CrCl using min SCr (ml/min) C-G CrCl using max SCr (ml/min) Wright eGFR using min Enz SCr (ml/min) Wright eGFR using max Enz SCr (ml/min) Wright eGFR using min Jaffe SCr (ml/min) Wright eGFR using max Jaffe SCr (ml/min) Min eGFR (ml/min) Max eGFR (ml/min) DTPA measured GFR (ml/min) 102.566.8112.0100.8113.879.266.8113.862.2 182.8137.6167.0155.4163.2128.4 182.8128.8 66.351.366.162.875.258.251.375.263.5 103.786.177.273.385.871.2 103.767.1 52.143.762.958.963.553.343.763.548.1 78.761.773.468.677.760.9 78.767.5 24.721.231.629.231.727.621.231.722.3 34.330.444.843.045.240.130.445.228.5 32.129.631.129.732.630.129.632.623.3 24.622.327.625.928.326.522.328.329.2 26

27. Carboplatin Dose Using Calvert (AUC = 6) 27

28. Carboplatin - Complications Too much – Bone marrow suppression Thrombocytopaenia – Bleeding Leucopaenia – Neutropaenia – Infections Anaemia Dose dependant Increased if prior therapy especially if also included cisplatin Too little – Decreased response 28

29. WEQAS Return (2012) MethodOverall Mean22.8319.8271.8136.3 Overall Number267290291288 VitrosMethod Mean30.4319.6272.9138.4 Number11 Vitros ID-MS traceableMethod Mean30.7319.5273.5139.3 Number17 16 EnzymaticMethod Mean27.2326.7276.1139.7 Number5356 54 Kinetic JaffeMethod Mean28.4322.0272.7137.7 Number49505251 Jaffe - IDMSMethod Mean16.9317.3270.2134.1 Number124148146 29

30. NEQAS Return (2012) Overall Mean74.2CV8.2 Number543 Dry Slide (1)Mean71.4CV2.6 Number59 Comp. Kin. Jaffé (4)Mean73.7CV7.2 Number339 Trad. Kin. Jaffé (1)Mean83.3CV8.5 Number60 Enzymatic (2)Mean72.1CV3.8 Number134 LowestMean67CV2.8 HighestMean83.3CV8.5 30

31. Carboplatin Dose (AUC=6) 45 yr old women weighing 65 kg using C&G and Calvert formula Serum creatinine = 83 umol/L – Carboplatin dose = 612 mg Serum creatinine = 67 umol/L – Carboplatin dose = 726 mg True change serum creatinine and CrCL = 0 Change in dose = 116 mg = increase 19% 31

32. 32 Effect of Change in Serum Creatinine Calibration on Prevalence of Low GFR in Nondiabetics in NHANES III. (Clase et al. J Am Soc Nephrol 2002;13:2811-2816) (i.e. uncalibrated – 20.3 umol/l) Lab used in Third National Health and Nutrition Examination Survey (NHANES) Results adjusted to method used in Modification of Diet in Renal Disease Study (MDRD) CKD 1 2 3 4+ CKD 1 2 3 4+

33. Serum Creatinine and Calculated Creatinine Clearance / Estimated Glomerular Filtration Rate Survey 33

34. Assay + Instrument – Lab. 34 MethodNumber% (100) Manufacturer’s Jaffe34.8 Man. Kinetic Jaffe711.3 Man. Comp. Kinetic Jaffe34.8 Man. Enzymatic1016.1 Man. Jaffe + Enz914.5 Manufacturer only1727.4 Jaffe23.2 Kinetic Jaffe34.8 Compensated Jaffe11.6 Enzymatic58.1 Jaffe + Enz11.6 YES!11.6 Total62100 IDMS Traceable5791.9

35. Assay + Instrument - POCT 35 AnalyserNumberMethod Roche1? Nova3StatSensor Abaxix Piccolo1Enzymatic Total5 N/A36 Total Respondents41 No response21 IDMS Traceable2 Yes 5 No = 7!

36. Serum Creatinine and Calculated Creatinine Clearance / Estimated Glomerular Filtration Rate Survey 36

37. Adjustment Factors 37 Adjustment FactorsNumber -26.5 umol/L1 -26 umol/L3 -11 umol/L1 Adjust if bilirubin high1 Total6 Yes8! No50 No response4

38. Serum Creatinine and Calculated Creatinine Clearance / Estimated Glomerular Filtration Rate Survey 38

39. cCrCl and / or eGFR 39 11 labs calculated a creatinine clearance using serum and urine creatinine. No adjustment for height and weight Question was really looking to see if anyone was using C&G etc eGFR FormulaNumber MDRD19 175 with slope and intercept17 175 no slope and intercept4 1862 Not stated8 Total50 One lab didn’t know whether they were using a slope and intercept (they were) and they were reporting eGFR to non-patients only

40. Serum Creatinine and Calculated Creatinine Clearance / Estimated Glomerular Filtration Rate Survey 40

41. 41 ProfessionFormulaNumber OncologistsMDRD2 OncologistsC&G4 OncologistsWright (no CK)1 OncologistsMeasured CrCl1 OncologistNK1 PharmacistMDRD1 PharmacistC&G8 PharmacistSchwartz1 Paed TransplantSchwartz1 HaematologyC&G1 RenalMDRD1 DiabetesNK1 RadiologyNK1 DVT ServiceMDRD1 Not Known 21 Total46 Respondents36/62

42. Role of the Clinical Biochemist 42 Clinical biochemists in the UK are leading the way in promoting the contribution of laboratory medicine to healthcare. 4.3.4 Promoting the contribution of laboratory medicine Consultants in Clinical Biochemistry: The future – RCPATH/ACB 2009 4.3.5 Optimising knowledge management Recommendation: Consultants in charge of NHS clinical biochemistry departments should recognise the growing importance of knowledge management and take responsibility for ensuring implementation in a coordinated manner. ACB statement on laboratory assessment of kidney function –Nov. 2010 Clinical users should be made aware that significant changes in estimated glomerular filtration rate might occur when a change in serum creatinine method is made. Examples of users likely to require well documented notification include renal physicians, oncologists, pharmacists, paediatricians and general practitioners

43. Healthcare Professionals Using SCr to Calculate CrCl and / or GFR and the Formula Used 43 SurveyNumber / Percent Respondents36 Don’t know21 Non respondents26 Don’t know47 Don’t know76% Do know24%

44. 44 Serum Creatinine and eGFR Where Are We Now?

45. We need to be out there for the good of our profession, but much more importantly, to ensure optimum patient outcomes 45