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Creatinine Definitive Method: IDMS.
Reference Method:
Jaffe reaction with pretreatment using fuller's earth or
Common Method:
Modified Jaffe Reaction - Example shown Component of 917 Analyser System.
Creatinine + Picric Acid (Alkaline) ===> Creatinine Picrate Acid Complex (Red Colour)
3-4% CV.
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Other Methods:
| Jaffe Reaction | Various Kinetic methods | Good accuracy and precision Problems with interference. Creatinine Amidohydrolase | Enzymatic hydrolysis to creatine | Couple to indicator reaction Reference Method | Highly Accurate Creatinine Amidohydrolase | Coupled enzymatic reaction linked to peroxidase indicator | Used in Dry Slide Technology
| HPLC | Cation exchange or reverse phase using UV detector | Good reference method but not practical for general lab use.
| HPLC/GCMS | Isotope dilution GC/MS | Good reference method to standardise other methods (eg modified Jaffe).
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eGFR
The eGFR calculation now means we have to be more accurate in our serum creatinine measurments for the calculation to be valid. It has been recommended that assays should be made to standardise results on assays particularly around 88.4 umol/L where optimal performance is desired.
See Myers et al Clinical Chemistry 2006. 52:1
Kidney foundation now recommend eGFR on all patients when a serum Creatinine is measured.
Looking for early signs of Renal failure.
Based on the MDRD calculation of GFR based on Serum Creat, Age, Sex and (ethnicity if Black).
Not validated in children.
Study done using Beckman Synchron analyser (Modified Jaffe)
Recomendations for Improving Serum Creatinine Measurement: A Report from the Laboratory Working Group of the National Kidney Disease Education Program.
