New Research Reveals How Accurately Doctors Can Monitor Kidney Disease Progression Using Blood Tests

Kidney disease affects millions across the UK, but doctors face a significant challenge: determining whether a patient’s kidneys are genuinely getting worse or simply fluctuating naturally over time. New research published by the British Medical Journal has examined how accurately two blood markers—creatinine and cystatin C—can track kidney function in patients with moderate chronic kidney disease (CKD).

The eGFR-C study, conducted by researchers across multiple NHS trusts and universities, directly addresses a critical gap in clinical practice. Glomerular filtration rate, or GFR, measures how effectively kidneys filter waste from the blood. Rather than measuring GFR directly, which requires invasive testing, doctors use estimation equations based on blood tests to calculate it. These equations form the foundation of kidney disease monitoring in general practice and hospital nephrology clinics.

“The challenge with existing GFR equations is that they weren’t designed to accurately track changes over time,” explains the research team. Currently, the NHS relies heavily on the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, which uses creatinine measurements. However, the accuracy of these estimates—particularly when monitoring disease progression—has long been questioned by clinicians.

The study compared several estimation approaches in people with moderate CKD (stage 3, with GFR between 30-59 mL/min/1.73m²). Researchers followed participants over time and measured how well different equations reflected actual changes in kidney function. One key finding concerns the accuracy metric known as P30—the percentage of results within 30 per cent of true measurements. While existing equations achieve P30 values between 73-93 per cent at a single point in time, their accuracy when tracking changes over months and years has remained less well understood.

The research examined whether adding cystatin C—an alternative blood marker—alongside creatinine improved accuracy. Cystatin C is a smaller protein filtered by the kidneys that may reflect kidney function differently than creatinine, which is affected by muscle mass and diet. In older patients, for example, equations combining both markers achieved accuracy rates around 86 per cent, compared with 81 per cent for creatinine-only equations.

Understanding longitudinal accuracy matters enormously in practice. If a patient’s estimated GFR falls from 50 to 45 mL/min/1.73m², is this genuine disease progression requiring urgent intervention, or merely normal biological variability? The measurement error built into GFR equations means that a drop below a certain threshold—typically about 14 per cent using current equations—is needed to confidently declare true decline. This can delay recognition of genuine progression or, conversely, trigger unnecessary concern from false alarms.

The eGFR-C researchers also examined whether combining GFR estimates with other markers, such as the albumin-to-creatinine ratio (which measures protein leakage in urine), improved the ability to predict which patients would develop progressive kidney disease. This has practical implications for deciding which patients need specialist nephrology referral or more intensive monitoring.

Recent research from Canada, Denmark and Scotland highlighted additional challenges. A newer prediction model called KDpredict showed improved accuracy compared with traditional kidney failure risk equations, particularly because it accounts for the competing risk of death in older patients with CKD. An 80-year-old man with moderately reduced kidney function faces significant mortality risk alongside kidney failure risk—a distinction that affects clinical decision-making but is often overlooked.

These findings come at a time when NHS kidney disease services face increasing demand. Approximately 3.5 million people in the UK have CKD, though many remain undiagnosed. Early detection and accurate monitoring are critical because slowing kidney disease progression prevents or delays the need for dialysis and kidney transplantation.

For GPs managing patients with CKD in the community, the implications are significant. Accurate longitudinal monitoring helps distinguish patients needing urgent hospital referral from those requiring routine follow-up. For hospital nephrologists, it improves confidence in treatment decisions, including when to initiate medications that slow disease progression or modify risk factors.

The cost of cystatin C testing—higher than standard creatinine—has limited its uptake in the NHS, even where it might provide clinical benefit. The eGFR-C study’s findings directly inform whether the NHS should invest in wider cystatin C testing or optimise existing creatinine-based approaches.

Key Takeaways

• Different GFR estimation equations vary in accuracy, particularly when tracking kidney disease changes over time rather than at single time points
• Combining creatinine with cystatin C may improve accuracy in certain populations, though cost-effectiveness remains under evaluation
• Accurate monitoring helps distinguish genuine kidney disease progression from normal biological variation
• Individual risk prediction models that account for death risk alongside kidney failure risk are emerging as more useful tools in older patients

What This Means for Kent Residents

Residents with chronic kidney disease across Kent and Medway are likely to benefit from these research findings as they filter into NHS practice. The NHS Kent and Medway ICB commissions kidney services across local hospital trusts including East Kent Hospitals University NHS Foundation Trust and Maidstone and Tunbridge Wells NHS Trust. If this research supports adoption of more accurate monitoring approaches, patients attending nephrology clinics or being followed by their GP with CKD should expect more reliable tracking of their kidney function over time. This translates to better clinical decisions about treatment intensity and timing of specialist referral. If you have CKD or risk factors such as diabetes or high blood pressure, ask your GP about your GFR results and what they mean for your individual monitoring plan.