Sweden: A recent study has shown low estimated glomerular filtration rate based on both creatinine and cystatin C (eGFRcr-cys) is more strongly and uniformly associated with adverse outcomes compared with low estimates based on creatinine alone (eGFRcr) in older patients.
The findings, published in the Annals of Internal Medicine, highlight the benefit of including cystatin C in GFR estimation.
The commonly accepted threshold of GFR to define chronic kidney disease (CKD) is less than 60 mL/min/1.73 m2. This threshold is partly based on associations between estimated GFR and the frequency of adverse outcomes. In older adults, the associations are weaker, which has created disagreement about the appropriateness of the threshold for these persons. In addition, the studies measuring these associations included relatively few outcomes and estimated GFR based on creatinine level, which may be less accurate in older adults.

Against the above background, Edouard L. Fu, Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden, and colleagues aimed to evaluate associations in older adults between eGFRcr versus eGFR based on creatinine and cystatin C levels and eight outcomes in a population-based cohort study conducted in Stockholm, Sweden from 2010 to 2019.
The study included 82,154 participants aged 65 years or older with outpatient creatinine and cystatin C testing. Hazard ratios were calculated for cardiovascular mortality, all-cause mortality, and kidney failure with replacement therapy (KFRT). Incidence rate ratios were calculated for recurrent hospitalizations, myocardial infarction or stroke, infection, heart failure, and acute kidney injury.
The study led to the following findings:
The associations between eGFRcr-cys and outcomes were monotonic, but most associations for eGFRcr were U-shaped.
eGFRcr-cys was more strongly associated with outcomes than eGFRcr. For example, the adjusted hazard ratios for 60 versus 80 mL/min/1.73 m2 for all-cause mortality were 1.2 for eGFRcr-cys and 1.0 for eGFRcr, and for KFRT they were 2.6 and 1.4, respectively.
Similar findings were observed in subgroups, including those with a urinary albumin–creatinine ratio below 30 mg/g.
"Estimated glomerular filtration rate based on both creatinine and cystatin C was more strongly and uniformly associated with cardiovascular events than estimates based on creatinine alone," the researchers wrote.
Nearly one-third of individuals were reclassified into a different severity category after recalculation.
Reference:
Fu EL, Carrero JJ, Sang Y, Evans M, Ishigami J, Inker LA, Grams ME, Levey AS, Coresh J, Ballew SH. Association of Low Glomerular Filtration Rate With Adverse Outcomes at Older Age in a Large Population With Routinely Measured Cystatin C. Ann Intern Med. 2024 Jan 30. doi: 10.7326/M23-1138. Epub ahead of print. PMID: 38285982.