Changes to serum creatinine methods / calibration must only be instituted after consultation with clinical colleagues, especially those in specialist units such as renal and oncology. One must also have assurance that those immediate colleagues will liaise with their colleagues in regional centres to whom they refer their patients. Indeed, it may be prudent to do so oneself. Why do I say this - read on!

The use of eGFR calculated using the abbrMDRD formula to detect CKD has become widespread and indeed in some countries mandatory. Following its introduction the lack of consistency of serum creatinine results and hence eGFR between laboratories soon became apparent. So much so that recommendations for improving serum creatinine measurment were published in the USA by the NKDEP Laboratory Working Group (Clin Chem 2006;52:5-18) whilst in the UK Finlay MacKenzie recommended the use of method specific slope (and intercept) adjustment of serum creatinine results to give IDMS  equivalent values for use in the abbrMDRD equation (F MacKenzie - A Personal View. UKNEQAS March 2006).

Since then many laboratories have begun to report serum creatinine results that are calibrated against an IDMS reference method or, in some cases, have begun to report creatinine results adjusted to give results equivalent to an IDMS reference method. Whilst these changes are well intentioned they will almost certainly produce serum creatinine results lower than those produced previously by up to approximately 20 umol/L. This in turn will produce a higher GFR and lead to fewer patients being wrongly classified as having CKD. This is all well and good, but what effect will it have on drug dosing regimes based upon the previously higher creatinine results, or on calculated creatinine clearance results produced using the Cockcroft and Gault formula, first published in 1976? The answer is that some patients will be receiving higher doses of certain drugs than would have previously been the case thereby leading to toxic side effects e.g. myelosuppression and carboplatin.

This is a very real problem that has come to light in my region during the summer. Changing to a serum creatinine method whose calibrator is traceable to an IDMS reference procedure is the right thing to do, but must not be done without full consultation with clinical colleagues.

Mike




Dr. Mike Bosomworth
Head of Blood Sciences
Consultant Clinical Scientist

Tel. 0113 3922340      Fax 0113 3925174 
Mobile 07789 174344

Please visit our web-site at www.leedsteachinghospitals.com     

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