Understanding the Test Discrepancy
A growing body of research indicates that mismatches between two common kidney function tests could reveal greater health risks than either test alone. Traditionally, clinicians have relied on creatinine-based estimates of glomerular filtration rate (eGFR) to assess kidney health. A newer approach uses cystatin C, another biomarker, to calculate eGFR. When these two measurements diverge significantly, it may signal underlying issues that warrant closer monitoring.
What the Tests Measure
Creatinine is a waste product produced by muscles and cleared by the kidneys. Its concentration in blood helps estimate how well the kidneys are filtering. Cystatin C, produced by all nucleated cells, is less influenced by muscle mass and may provide a different perspective on kidney function, particularly in people with atypical muscle mass, the elderly, or certain chronic conditions.
The Significance of a Mismatch
Researchers found that individuals whose creatinine-based eGFR and cystatin C-based eGFR did not align had a higher risk of adverse outcomes, including progression to kidney failure, cardiovascular disease, and even mortality. This discrepancy may act as an early warning sign, prompting doctors to investigate potential risk factors that a single test could miss.
How It Can Influence Care
When tests disagree, clinicians may consider several steps: repeating the assessments, evaluating for factors that artificially alter results (such as body composition, medications, or inflammatory conditions), and exploring additional markers of kidney and heart health. The information can guide decisions about lifestyle interventions, medication adjustments, and the need for specialist referral.
Who Might Benefit Most
Discrepancies between creatinine and cystatin C are particularly informative for patients with abnormal muscle mass, older adults, athletes, or those with chronic illnesses like diabetes or hypertension. In these groups, reliance on a single test could either overestimate or underestimate kidney function, masking evolving risk. Using both measurements together can provide a more nuanced risk profile and help tailor prevention strategies.
What the Findings Mean for Everyday Health
For individuals without known kidney disease, a disagreement between the tests doesn’t guarantee trouble, but it does warrant a conversation with a healthcare provider. It can prompt a more comprehensive assessment of cardiovascular risk, blood pressure control, and metabolic health. For patients with existing kidney disease, the dual-test approach may refine staging and track progression with greater precision.
Moving Toward Broader Use
As evidence accumulates, some clinicians are integrating both creatinine and cystatin C measurements into routine care for at-risk populations. Many laboratories already offer both tests, and insurance coverage is expanding in some regions. The goal is to catch subtle shifts in kidney and heart health early, allowing for timely interventions that can slow disease progression.
Bottom Line
Discrepancies between creatinine-based and cystatin C-based eGFR readings are more than a technical curiosity; they can be meaningful indicators of higher risk for kidney failure, heart disease, and death. By recognizing and acting on these differences, patients and clinicians can pursue earlier, proactive steps to protect kidney and overall health.
