Multimorbidity associated with creatinine–cystatin C eGFR discordance in UK Biobank

An observational study in Nephrology Dialysis Transplantation examined associations between multimorbidity and discordant kidney function estimates in over 400,000 UK Biobank participants. Researchers calculated creatinine-based and cystatin C-based eGFR using European Kidney Function Consortium equations and counted self-reported long-term conditions. Large negative discordance was defined as cystatin C-based eGFR more than 30% below creatinine-based eGFR.

Multimorbidity, defined as at least two long-term conditions, occurred in 33% of the cohort and 63% of participants with large negative discordance. Compared with participants reporting no conditions, those with four or more had an adjusted odds ratio of 4.64 (95% CI 4.13–5.21) for large negative discordance. Models adjusted for age, sex, body mass index, smoking and thyroid disease. Reassigning CKD stage using cystatin C rather than creatinine reclassified 15% of participants to a more advanced stage, with reclassification becoming more frequent as condition counts increased.

The authors suggest considering cystatin C alongside creatinine in people with multimorbidity to refine kidney function estimation and risk stratification. However, these observational associations do not establish causation or demonstrate improved outcomes from additional testing. Conditions were self-reported, and the available abstract does not report comparison with measured GFR; stage reclassification alone therefore does not establish which estimate was more accurate.