Measuring eGFR with cystatin C can strongly impact CKD staging

Measuring cystatin C-based eGFR strongly correlates with creatinine eGFR, but it can also have a significant impact on the staging of chronic kidney disease, according to data published in Kidney Medicine.

Cystatin C eGFR is often lower than creatinine eGFR, study researchers noted, therefore using cystatin C-based eGFR measurements can label many patients with a later stage of CKD.

Eric Raphael Gottlieb

“Cystatin C is gaining importance as an alternative biomarker to creatinine for estimating kidney function (glomerular filtration rate, GFR), and was recommended by a national American Society of Nephrology/National Kidney Foundation taskforce for verification of creatinine-based estimates with the removal of the African American race multiplier in 2021,” Eric Raphael Gottlieb, MD, MS, from the department of medicine at Mount Auburn Hospital in Massachusetts, told Healio. “However, there is limited real-world data to guide its use and to determine which patients are likely to have significant alterations in GFR estimates and chronic kidney disease staging when cystatin C is tested. We analyzed data from a large clinically and demographically diverse cohort of patients at Brigham and Women’s Hospital, the Dana Farber Cancer Institute and several associated outpatient lab centers in the Boston area to answer this question.”

In a retrospective observational cohort study, Gottlieb and colleagues analyzed data of 1,783 inpatients and outpatients with CKD. Patients had cystatin C and creatinine levels taken within 24 hours at Brigham Health-affiliated labs.

Researchers calculated eGFR using the 2021 CKD-Epidemiology Collaboration equation, then determined CKD stages based on creatinine and cystatin C using Kidney Disease: Improving Global Outcomes guidelines.

Researchers performed univariate and multivariable linear and logistic regressions, then stratified results by CKD stage. Changes in staging were measured using a paired nonparametric Wilcoxon test.

Overall, cystatin C-based eGFR was associated with creatinine-based eGFR. Analyses revealed the cystatin C-based eGFR led to a CKD stage progression in 27% of patients, a change to an earlier stage in 7% and no change in 66% of patients.

“We were impressed by the proportion of patients (27% overall and 57% with borderline low eGFR for their creatinine-based stage) who would be classified as having a higher chronic kidney disease stage when cystatin C was tested,” Gottlieb and colleagues wrote. “This was of particular importance for patients of older age and with more comorbid conditions. By contrast, cystatin C rarely indicated less severe kidney dysfunction than creatinine.”

Further, researchers identified a lower likelihood of progression to a later CKD stage with Black race. However, age and Elixhauser score correlated with a higher chance of changing to a later stage.

“Our study shows that utilization of cystatin C can lead to changes in CKD staging, which can impact clinical management. Cystatin C should be tested for verification of chronic kidney disease stage at baseline and at other critical points, such as when evaluating declining kidney function and determining drug dosing (for example, chemotherapeutics),” Gottlieb told Healio. “Nationally, there should be a focus on making this important test affordable and accessible to a wide, diverse spectrum of patients.”