A new global study led by NYU Langone Health researchers has found that a discrepancy between two common kidney function tests could be an early warning sign of serious health problems including kidney failure, heart disease, and even premature death.
Two Tests, Two Stories
Doctors typically check kidney health by measuring creatinine, a waste product from muscle breakdown that the kidneys filter from the blood.
However, newer guidelines also recommend measuring cystatin C, a small protein produced by all cells in the body.
While both are used to estimate kidney function, they can be influenced by different factors such as age, muscle mass, and illness. Using both markers together gives doctors a more accurate picture of how well the kidneys are working.
What the Study Found
The research team analyzed data from over 860,000 people from multiple countries. Each participant had both creatinine and cystatin C measured on the same day and was followed for about 11 years.
Shockingly, more than one-third of hospitalized patients had a cystatin C-based kidney function reading that was 30% lower than their creatinine-based one, a gap linked to a much higher risk of death, heart failure, and kidney disease progression.
Even among seemingly healthy individuals, around 11% showed similar differences, suggesting early, hidden kidney issues.
Why It Matters
According to Dr. Morgan Grams, co-author of the study, “Measuring both creatinine and cystatin C provides a clearer, earlier signal of kidney trouble, especially in older or sicker adults.”
This dual testing can also help doctors prescribe safer medication doses, since kidney function affects how the body processes many drugs, including antibiotics and cancer treatments.
Cystatin C Testing Still Rare
Despite its benefits, cystatin C testing remains underused. A 2019 survey found that fewer than 10% of U.S. laboratories performed it in-house. Fortunately, large labs such as Quest Diagnostics and Labcorp now offer the test, making it more accessible.
Dr. Josef Coresh, another lead author, emphasized that “more hospitals and clinics should start using cystatin C testing. It can reveal crucial information about a patient’s overall health that creatinine alone might miss.”
The Bigger Picture
The findings come as part of the Chronic Kidney Disease Prognosis Consortium, the largest international effort to understand kidney health. The same research group also reported that chronic kidney disease (CKD) has now become the ninth leading cause of death worldwide.
Early detection through both creatinine and cystatin C testing could help millions receive timely care, reducing the need for dialysis or kidney transplants later on.
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✅ Final Takeaway
If you or a loved one are at risk for kidney problems due to diabetes, high blood pressure, or aging, ask your doctor about cystatin C testing. One extra test could make a life-changing difference.
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