Frequency of Renal Monitoring - Creatinine and Cystatin C (FORM-2C): an observational cohort study of patients with reduced eGFR in primary care

Abstract

Background: Monitoring is the mainstay of chronic kidney disease management in primary care; however, there is little evidence about the best way to do this.

Aim: To compare the effectiveness of estimated glomerular filtration rate (eGFR) derived from serum creatinine and serum cystatin C to predict renal function decline among those with a recent eGFR of 30-89 ml/min/1.73 m².

Design and setting: Observational cohort study in UK primary care.

Method: Serum creatinine and serum cystatin C were both measured at seven study visits over 2 years in 750 patients aged ≥18 years with an eGFR of 30-89 ml/min/1.73 m² within the previous year. The primary outcome was change in eGFR derived from serum creatinine or serum cystatin C between 6 and 24 months.

Results: Average change in eGFR was 0.51 ml/min/1.73 m²/year when estimated by serum creatinine and -2.35 ml/min/1.73 m²/year when estimated by serum cystatin C. The c-statistic for predicting renal decline using serum creatininederived eGFR was 0.495 (95% confidence interval [CI] = 0.471 to 0.519). The equivalent c-statistic using serum cystatin C-derived eGFR was 0.497 (95% CI = 0.468 to 0.525). Similar results were obtained when restricting analyses to those aged ≥75 or <75 years, or with eGFR ≥60 ml/min/1.73 m². In those with eGFR <60 ml/min/1.73 m², serum cystatin C-derived eGFR was more predictive than serum creatinine-derived eGFR for future decline in kidney function.

Conclusion: In the primary analysis neither eGFR estimated from serum creatinine nor from serum cystatin C predicted future change in kidney function, partly due to small changes during 2 years. In some secondary analyses there was a suggestion that serum cystatin C was a more useful biomarker to estimate eGFR, especially in those with a baseline eGFR <60 ml/min/1.73 m².

Keywords: chronic kidney diseases; creatinine; cystatin C; estimated glomerular filtration rate; primary care.

Figure 1.

Participant flow through the FORM-2C study. FORM-2C = Frequency of Renal Monitoring — Creatinine and Cystatin C.

Figure 2.

Mean and 95% CIs for quartiles of a) eGFR-serum creatinine and b) eGFR-serum cystatin C calculated from the FORM-2C cohort at baseline and at 24 months. CKD–EPI = Chronic Kidney Disease Epidemiology Collaboration. eGFR = estimated glomerular filtration rate. FORM-2C = Frequency of Renal Monitoring — Creatinine and Cystatin C.