Standard kidney function tests underestimate chronic kidney disease in people with cancer

Commonly used blood-based estimates of kidney function substantially understate how many people with cancer have chronic kidney disease, according to new research being presented at ASN Kidney Week 2026 in Denver, Colorado, from October 22 to 25. In a study of 1,200 adults with solid tumors, investigators directly measured each participant’s glomerular filtration rate (GFR), the rate at which the kidneys filter blood, using a specialized clearance marker, and then compared that measured value with the estimated GFR (eGFR) values that clinicians typically calculate from blood levels of the proteins creatinine and cystatin C. The comparison revealed sizable gaps: the prevalence of chronic kidney disease (CKD) was 18.9% when based on measured GFR, but only 10.2% when based on creatinine alone and 15.7% when based on creatinine combined with cystatin C.

The discrepancies were most consequential in the ranges that guide treatment decisions. Among participants whose measured GFR fell between 45 and 59 ml/min/1.73 m2, indicating mild to moderate CKD, 72.1% had a creatinine-based eGFR above 60, a value generally interpreted as normal kidney function. Among those with a measured GFR below 45 ml/min/1.73 m2, indicating more advanced CKD, 52.5% had a creatinine-based eGFR above 45. Adding cystatin C to the creatinine-based calculation improved the agreement between measured and estimated values, but concordance remained poor overall. Because drug clearance often declines as kidney function declines, these thresholds matter directly for decisions about which anticancer drugs patients are eligible to receive and at what doses.

Corresponding author Veronica Torres Costa e Silva, MD, PhD, of the University of São Paulo Medical School in Brazil, said the results suggest that errors in GFR estimation may contribute to exceeding toxicity in patients with cancer receiving anticancer therapy. She pointed to cisplatin as an example: most recommendations state that patients with a GFR of 45 to 60 ml/min/1.73 m2 should have a dose reduction of 25 to 50%, while those with a GFR below 45 ml/min/1.73 m2 should not be considered eligible for the drug. If estimates place a patient’s GFR above the true measured value, she explained, patients may receive exceedingly higher doses and experience a higher frequency of toxicity because clinicians are not able to accurately assess GFR and make accurate dose adjustments.

The study, titled “Discrepancy in Glomerular Filtration Rate in Patients with Cancer,” was conducted in adults with solid tumors and compared measured GFR, obtained with a specialized clearance marker, against the two estimation approaches in routine clinical use. Measured GFR differs from estimated GFR in that it relies on a specialized clearance marker to assess kidney filtration directly, rather than deriving a value from blood protein levels through statistical formulas. The estimation approaches examined in the study are the ones commonly used in clinical practice, making the reported gaps relevant to everyday oncology care rather than to specialized testing alone.

The findings are being presented at a scientific meeting and, as with other conference presentations, have not yet appeared as a peer-reviewed publication; the reported prevalence figures and agreement rates reflect this specific cohort of 1,200 adults with solid tumors. Even so, the pattern reported by the investigators, in which creatinine-based estimates classified most patients with measured mild to moderate CKD as having normal kidney function, and in which roughly half of patients with measured advanced CKD were estimated above the eligibility threshold, underscores a potential safety concern for dose adjustments in oncology. The results also indicate that while incorporating cystatin C moves estimates closer to measured values, estimation errors persist, suggesting that measured GFR may be needed in some clinical situations where precise kidney function assessment determines drug eligibility and dosing.

Subject of Research: Discrepancies between measured and estimated glomerular filtration rate in adults with solid tumors

Article Title: Standard kidney function tests underestimate chronic kidney disease in people with cancer

Article References: Standard kidney function tests underestimate chronic kidney disease in people with cancer. Original publication (Bibliographic details unavailable.)

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Keywords: chronic kidney disease, glomerular filtration rate, cystatin C, creatinine, cancer, nephrology, cisplatin, chemotherapy dosing, kidney function tests, drug toxicity, ASN Kidney Week 2026, oncology