Study Reveals Kidney Function Test Discrepancies Increase Health Risks

A recent study led by researchers from NYU Langone Health has found that discrepancies between two common kidney function tests may predict a higher risk of serious health problems, including kidney failure and heart disease. The research highlights the importance of measuring both creatinine and cystatin C levels to better assess kidney function and associated health risks.

For decades, healthcare providers have relied on blood creatinine levels to monitor kidney filtration rates. More recently, guidelines have recommended the use of cystatin C, a protein produced by all body cells, as an additional measure. This study suggests that using both tests together can provide a more comprehensive view of kidney health, particularly in patients who are ill or elderly.

The findings, published online on November 7, 2025 in JAMA and presented at the American Society of Nephrology’s annual Kidney Week conference, reveal alarming discrepancies in test results. Specifically, more than a third of hospitalized participants showed a cystatin C-based kidney function reading that was at least 30% lower than that based on creatinine levels.

Dr. Morgan Grams, a co-corresponding author of the study, emphasized the significance of these findings: “Our research underscores the necessity of utilizing both creatinine and cystatin C to obtain an accurate understanding of kidney performance, especially among older and sicker individuals.” He noted that evaluating both biomarkers could identify a larger number of patients with poor kidney function earlier in the disease process.

The study analyzed healthcare records and blood tests from 860,966 individuals across six nationalities. Participants had both creatinine and cystatin C levels measured on the same day, with follow-ups an average of 11 years later. Researchers considered various factors that could influence the test results, including smoking, obesity, and cancer history.

This investigation is part of the international Chronic Kidney Disease Prognosis Consortium, which aims to better understand chronic kidney disease (CKD), now recognized as the ninth leading cause of death worldwide. According to the study, individuals whose cystatin C-based measures were significantly lower than creatinine-based measures faced increased risks for mortality, heart disease, and kidney failure requiring dialysis or transplantation.

The study also revealed that a record number of people globally are living with chronic kidney disease, reinforcing the need for effective early detection methods. Dr. Grams pointed out that timely identification of kidney issues can facilitate prompt treatment, potentially preventing more severe interventions such as dialysis.

Despite the importance of cystatin C testing, the study found that less than 10% of clinical laboratories in the United States performed it in-house as of a 2019 survey. The two largest laboratories, Quest Diagnostics and Labcorp, have since started offering the test. Dr. Josef Coresh, another co-corresponding author, urged clinicians to take advantage of the increasing availability of cystatin C testing. “Failing to utilize this information may result in missed opportunities to better manage patients’ health,” he stated.

The findings serve as a critical reminder of the importance of comprehensive evaluation in managing kidney health. By employing both creatinine and cystatin C measurements, healthcare providers can enhance their ability to detect kidney dysfunction and improve patient outcomes.