Discordance Between Creatinine-Based and Cystatin C-Based Estimated GFR: Interpretation According to Performance Compared to Measured GFR

Rationale & Objective: Use of cystatin C in addition to creatinine to estimate glomerular filtration rate (estimated glomerular filtration rate based on cystatin C [eGFRcys] and estimated glomerular filtration rate based on creatinine [eGFRcr], respectively) is increasing. When eGFRcr and eGFRcys are discordant, it is not known which is more accurate, leading to uncertainty in clinical decision making.Study Design: Cross-sectional analysis.Setting & Participants: Four thousand fifty participants with measured glomerular filtration rate (mGFR) from 12 studies in North America and Europe.Exposures: Serum creatinine and serum cystatin C.Outcome(s): Performance of creatinine-based and cystatin C-based glomerular filtration rate estimating equations compared to mGFR.Analytical Approach: We evaluated the accuracy of eGFRcr, eGFRcys, and the combination (eGFRcr-cys) compared to mGFR according to the magnitude of the difference between eGFRcr and eGFRcys (eGFRdiff). We used CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations to estimate glomerular filtration rate. eGFRdiff was defined as eGFRcys minus eGFRcr and categorized as less than -15, -15 to <15, and >= 15 mL/min/1.73 m(2) (negative, concordant, and positive groups, respectively). We compared bias (median of mGFR minus eGFR) and the percentage of eGFR within 30% of mGFR.Results: Thirty percent of participants had discordant eGFRdiff (21.0% and 9.6% negative and positive eGFRdiffs, respectively). In the concordant eGFRdiff group, all equations displayed similar accuracy. In the negative eGFRdiff groups, eGFRcr had a large overestimation of mGFR (-13.4 [-14.5 to -12.2] mL/min/1.73 m(2)) and eGFRcys had a large underestimation (9.9 [9.111.2] mL/min/1.73m(2)), with opposite results in the positive eGFRdiff group. In both negative and positive eGFRdiff groups, eGFRcrcys was more accurate than either eGFRcr or eGFRcys. These results were largely consistent across age, sex, race, and body mass index.Limitations: Few participants with major comorbid conditions.Conclusions: Discordant eGFRcr and eGFRcys are common. eGFR using the combination of creatinine and cystatin C provides the most accurate estimates among persons with discordant eGFRcr or eGFRcys.

Automated summary

This study found that the combination of cystatin C and creatinine provides the most accurate estimates of glomerular filtration rate, especially when eGFRcr and eGFRcys are discordant.