Cystatin C-Based eGFR May Affect Staging

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Cystatin C- and creatinine-based estimated glomerular filtration rate (eGFR) values are strongly correlated with each other, whereas cystatin C-based estimates can have a substantial impact on chronic kidney disease (CKD) staging, reports a study in Kidney Medicine.

The retrospective analysis included 1783 patients who had cystatin C and creatinine levels measured within 24 hours of each other in a large health system for over 4 years. Analysis focused on correlations between eGFR values based on cystatin C versus creatinine and their impact on CKD staging and delivery of kidney care.

The results showed that cystatin C-based eGFR was “very strongly correlated” with creatinine-based eGFR. In multivariable analyses, older age was progressively associated with lower cystatin C-based eGFR at a given creatinine-based eGFR level, at all stages of CKD.

Compared with creatinine eGFR, cystatin C eGFR was associated with a change to a later CKD stage in 27% of patients, an earlier stage in 7%, and no change in 66%. Change to a later stage was less likely for Black compared with White patients (odds ratio [OR], 0.53). Older patients were more likely to have change to a later stage (OR, 1.03/year), as were those with higher comorbidity (OR, 1.22/point on an Elixhauser score). The most common reason for ordering a cystatin C measurement was diagnostic workup (48%), followed by transplant evaluation (21%).

A recent report by the Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases called for increased use of cystatin C to confirm eGFR in clinical decision-making. The new analysis shows a very strong correlation between cystatin C- and creatinine-based eGFR in a large and diverse patient sample.

Cystatin C led to a CKD change in approximately one-third of patients, mainly to a later stage. These changes are affected by factors such as age, race, and comorbidity. The authors discuss the implications for care delivery as cystatin C measurement comes into routine clinical use [Gottlieb ER, et al. Estimated GFR with cystatin C and creatinine in clinical practice: A retrospective cohort study. Kidney Med 2023; 5:100600; doi: 10.1016/j.xkme.2023.100600].