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Implications of method specific creatinine adjustments on General Medical Services chronic kidney disease classification

¹ Department of Chemical Pathology, Queen’s Hospital, Burton-on-Trent, UK
² Department of Clinical Biochemistry, The Ipswich Hospital, Ipswich, UK

Correspondence to:
Professor T M Reynolds
Department of Chemical Pathology, Queen’s Hospital, Burton-on-Trent DE13 0RB, UK; tim.reynolds{at}burtonh-tr.wmids.nhs.uk Aims: To evaluate the impact of different equations for calculation of estimated glomerular filtration rate (eGFR) on general practitioner (GP) workload.

Methods: Retrospective evaluation of routine workload data from a district general hospital chemical pathology laboratory serving a GP patient population of approximately 250 000. The most recent serum creatinine result from 80 583 patients was identified and used for the evaluation. eGFR was calculated using one of three different variants of the four-parameter Modification of Diet in Renal Disease (MDRD) equation.

Results: The original MDRD equation (eGFR₁₈₆) and the modified equation with assay-specific data (eGFR_175corrected) both identified similar numbers of patients with stage 4 and stage 5 chronic kidney disease (ChKD), but the modified equation without assay specific data (eGFR₁₇₅) resulted in a significant increase in stage 4 ChKD. For stage 3 ChKD the eGFR₁₇₅ identified 28.69% of the population, the eGFR₁₈₆ identified 21.35% of the population and the eGFR_175corrected identified 13.6% of the population.

Conclusions: Depending on the choice of equation there can be very large changes in the proportions of patients identified with the different stages of ChKD. Given that according to the General Medical Services Quality Framework, all patients with ChKD stages 3–5 should be included on a practice renal registry, and receive relevant drug therapy, this could have significant impacts on practice workload and drug budgets. It is essential that practices work with their local laboratories.