Is it Time for a Kidney Stress Test?

When it comes to kidney health, the tools we have traditionally used, like the estimated

glomerular filtration rate (eGFR), only tell part of the story.

Relying on eGFR as the primary measure of kidney function is like using only a resting heart rate to judge cardiac health. It provides a general sense of performance but misses the crucial detail of how the organ responds under pressure. Cardiologists would never rely on just one static number. They use dynamic tools like a cardiac stress test, where they observe how the heart performs during exercise. This test helps them diagnose hidden issues, assess a patient’s risk for future events, and create a precise treatment plan.

Kidneys, much like the heart, must adapt during times of physiological stress (after surgery, during a severe illness, or even after a large meal). Without a way to measure this adaptability, we risk missing early signs of trouble. This allows damage to go unchecked for months or years until a patient lands in the emergency room.

Why Do We Need Dynamic Measures for Kidney Health?

Historically, kidney health has been monitored using an oversimplified measure called estimated GFR. This number is derived from one of over two dozen equations that use a fasting serum creatinine value to estimate how well the kidneys clear this waste product. While estimations are more practical than a measured GFR, which requires a 24-hour urine collection and multiple blood samples, they are not the complete picture.

Estimated GFR does a reasonably good job of identifying patients at higher risk for ER visits, hospital admissions, or surgery. However, a more transformative approach shifts the focus from tracking static markers to understanding how well the kidneys can adapt to stress. This is where the concept of renal function reserve (RFR) comes into play, a measure of the kidney’s ability to increase its performance when needed. Just as a cardiac stress test reveals the heart's true capacity, an RFR assessment could clarify the risk a patient with kidney disease faces during surgery or illness.

What Is Renal Function Reserve, and Why Is It Important?

Renal function reserve is the "hidden strength" of the kidneys: the capacity to perform above baseline when the body demands it most. In healthy individuals, this reserve provides flexibility and adaptability. Increasing the function of the kidney to rebalance the body quickly. But in vulnerable individuals (such as after major surgery, during sepsis, or even following heavy meals), this lack of reserve can dramatically reduce the ability of the kidneys to rebalance the body's internal environment. The longer the body is out of balance, the more problems can arise. Just like when a patient with diabetes takes an oral glucose tolerance test, their body cannot process the sugar fast enough, and the values in the blood rise. When a patient with depleted renal reserve faces an acute metabolic load, such as a high-protein meal or sudden dehydration, their kidneys struggle to maintain equilibrium.

This inability to compensate can spiral out of control, leading to volume overload, a common and dangerous event in emergency rooms. Patients with existing risks, such as hypertension, diabetes, or prior heart attacks, are especially vulnerable. The consequences can be profound, including longer hospital stays, higher rates of complications, and increased financial burdens. In 2022 alone, over 131,000 Americans were newly diagnosed with kidney failure, with nearly 97% starting dialysis. Many of these cases were preceded by hospitalizations or ICU stays, moments when earlier detection of a depleted renal reserve might have changed the trajectory.

How Can We Rethink Kidney Care for the Future?

Rethinking kidney health means measuring what truly matters, not just average performance, but the ability to respond when it’s needed most. This includes identifying why patients are at risk and educating them on how stressors (like holiday feasts or dehydration) impact their kidneys, and addressing these risks before they progress to chronic or end-stage disease.

The future of kidney care lies in innovation, but first, we must acknowledge why current ICU tools aren’t enough. Dialysis effectively cleanses the blood, yet it doesn’t restore kidney function or support the organ’s own physiology. Likewise, arterial pumps such as Impella can improve systemic perfusion, but the kidney’s intrinsic autoregulation limits how much increased arterial flow actually improves filtration. What’s missing are approaches that directly support kidney physiology during vulnerable periods - real-time, organ-targeted strategies that help preserve filtration capacity when patients need it most.

Beyond the hospital, new wearables and implantables could empower individuals to monitor and manage their kidney health at home, potentially reversing the trajectory of kidney disease.

What Will It Take to Innovate Kidney Health?

The case for earlier, more nuanced monitoring, from renal function reserve to the role of urine as a vital sign, is compelling. By recognizing and supporting the kidneys’ full reserve, we can shift the arc of kidney disease toward recovery, not decline.

This vision requires collective action: clinicians, technologists, researchers, advocates, and payers working together to invest in research, education, and creative tools. If you’re passionate about innovation in medicine, consider how you might champion this emerging approach to kidney health. Together, we can help usher in a new era where moments of crisis become opportunities for renewed health and resilience.

About the Author: John Erbey, CEO and Founder of Roivios®, has over 25 years of visionary

leadership in the medical sector. With a Ph.D. from the University of Pittsburgh, Erbey is dedicated to pioneering transformative solutions, including the JuxtaFlow® Renal Assist Device (RAD), to shift the global focus from managing kidney decline to actively sustaining organ physiology. Discover more at roivios.com.

Disclaimer: This contribution is part of Healthcare Insights’ Industry Perspectives series. It was selected for publication based on its contribution to the dialogue surrounding renal innovation. Healthcare Insights does not endorse specific medical devices but provides a platform for industry leaders to share data-driven foresight. None of the information in this article should be construed as medical, financial, legal, or professional advice. Learn more about our terms and policies at healthcarein.org/legal.