eGFR Underestimates CKD in Patients with Cancer, Study Finds

Creatinine-based estimated glomerular filtration rate (eGFR) substantially underestimated the prevalence of chronic kidney disease (CKD) in patients with solid tumors compared with measured GFR (mGFR), according to findings presented at ASN Kidney Week 2026 in Denver, Colorado.^1,2 Adding cystatin C narrowed the gap, but agreement with mGFR remained poor, particularly at thresholds guiding chemotherapy eligibility and dosing.

“The results suggest that errors in GFR estimation may contribute to exceeding toxicity in patients with cancer receiving anticancer therapy,” Veronica Torres Costa e Silva, MD, PhD, of the University of São Paulo Medical School, said in a statement.² “I’ll give the example of cisplatin. Most recommendations state that patients with GFR of 45–60 ml/min/1.73m2 should have a dose reduction of 25–50%, and those with GFR below 45 ml/min/1.73m2 should not be considered eligible. This means that our patients are receiving exceedingly higher doses and having a higher frequency of toxicity because we are not capable of accurately assessing GFR and making accurate dose adjustments.”

GFR discrepancies are well recognized in the general population but have not been well characterized in patients with cancer.¹ The 2024 KDIGO CKD guideline recommends estimating GFR using both creatinine and cystatin C when cystatin C is available.³

How Often Did eGFR Misclassify Kidney Function in Patients with Cancer?

This cross-sectional analysis evaluated a prospective cohort of 1200 patients with active solid tumors at a tertiary cancer center in São Paulo, Brazil, recruited between April 2015 and September 2017. Serum creatinine and cystatin C were measured before treatment initiation using certified reference materials, on the same day as mGFR by plasma clearance of chromium 51-labeled EDTA.¹

Investigators calculated eGFR from creatinine alone and from creatinine plus cystatin C using the 2021 CKD-EPI equations. Mean age was 58.8 years, and 50.8% of patients were male. The most common cancer sites were breast (22.6%), prostate (19.8%), and gastrointestinal (13.4%), and 14.8% of patients had metastatic disease.¹

Mean mGFR was 78.5 mL/min/1.73 m². CKD prevalence was 18.9% by mGFR, compared with 10.2% by creatinine-based eGFR and 15.7% by creatinine plus cystatin C–based eGFR.¹

The greatest discrepancies occurred near clinically important cutoffs. Among patients with an mGFR of 45 to 59 mL/min/1.73 m², 72.1% had a creatinine-based eGFR > 60. Among those with an mGFR below 45, 52.5% had a creatinine-based eGFR > 45.¹

In these misclassified patients, eGFR overestimated kidney function rather than underestimating it.¹ The affected thresholds are critical for drug eligibility and dosing, as clearance of many drugs falls as kidney function declines.²

What Do GFR Discrepancies Mean for Chemotherapy Dosing?

The investigators concluded both eGFR equations largely underestimated CKD stages in this cohort, particularly at thresholds requiring decisions about drug eligibility and dose adjustment. They suggested errors in GFR estimation may contribute to excess toxicity in patients receiving anticancer therapy.¹

The investigators called for an urgent need to incorporate more robust instruments for assessing GFR in clinical practice.¹

References

1. Costa e Silva VT, Inker L, Caires RA, et al. Discrepancy in glomerular filtration rate in patients with cancer. Presented at: ASN Kidney Week 2026; October 22-25, 2026; Denver, CO. doi:10.1681/ASN.2026wydtyd36

2. American Society of Nephrology. Standard kidney function tests underestimate chronic kidney disease in people with cancer. EurekAlert! Published October 23, 2026. Accessed October 25, 2026. https://www.eurekalert.org/news-releases/1148355

3. Brooks A. KDIGO releases updated 2024 CKD clinical practice guideline. HCPLive. Published March 13, 2024. Accessed October 25, 2026. https://www.hcplive.com/view/kdigo-releases-updated-2024-ckd-clinical-practice-guideline