Reclassification of Chronic Kidney Disease Stage, Eligibility for Cystatin-C and Its Associated Costs in a UK Primary Care Cohort

Background and aims: Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) estimations of glomerular filtration rate (eGFR), compared to modification of diet in renal disease (MDRD), have superior performance in predicting renal, cardiovascular and mortality events. Cystatin-C further improves prediction. Our primary aim was to assess the change in prevalence and classification of CKD in converting from MDRD to CKD-EPI in an unselected primary care CKD population. Our secondary aims were to determine the eligibility for cystatin-C testing based on National Institute for Health and Care Excellence guidance and the associated costs.

Methods: eGFR data from an unselected UK primary care CKD cohort was studied to assess reclassification of CKD stages from MDRD to CKD-EPI, suitability for cystatin-C testing and its associated cost.

Results: A total number of 24,660 individuals had ≥2 MDRD eGFR results <60 mL/min/1.73 m2 >3 months apart (7.0% of adult population). The mean age was 75.2 (SD 11.4 years) with 15,265 (61.9%) females. Mean eGFR was 2.88 mL/min/1.73 m2 lower with CKD-EPI eGFR versus MDRD eGFR (49.7 vs. 46.8, t test p < 0.0001, 95% CI 2.85-2.91). 12.0% of individuals were re-categorised to a more or less advanced CKD stage, and 1.3% to a less advanced stage. The percentage of the population categorised as 3a-A1 CKD-EPI and therefore potentially suitable for cystatin-C was 2.8%. The estimated initial cost is €67.5 (£57.2) million with annual costs of €2.7 (£2.3) million for the United Kingdom.

Conclusions: The mean eGFR was lower with the CKD-EPI formula and individuals were more likely to be reclassified to more advanced CKD. This may be related to the higher mean age of this unselected population compared to previous studies. Refinements of eGFR formulae, CKD definitions and cystatin-C eligibility in unselected populations are required.