Your Kidney Test Might Look Normal—But It Could Be Hiding Serious Risk

Researchers have discovered that kidney function levels that appear normal on standard tests may actually signal significant disease risk when compared to what's typical for your age and sex. A new study from Karolinska Institutet in Sweden has created population-based reference charts and an online calculator to help doctors catch early kidney disease years before serious damage occurs, potentially transforming how clinicians screen for chronic kidney disease (CKD).

Why Standard Kidney Tests Might Be Missing the Problem?

The challenge with current kidney disease screening is straightforward: many patients aren't diagnosed until they've already lost more than half of their kidney function, when treatment options become severely limited. Chronic kidney disease affects an estimated 10 to 15 percent of adults worldwide and is expected to rank among the five leading causes of years of life lost by 2040. The problem lies in how doctors interpret kidney test results. A single cutoff value doesn't account for individual differences based on age and sex, meaning someone with genuinely low kidney function for their age might be told their results are "normal".

The research team analyzed health data from more than 1.1 million adults in the Stockholm region of Sweden, representing about 80 percent of residents between 40 and 100 years of age. They examined nearly seven million estimated glomerular filtration rate (eGFR) test results—the most common measure used to assess kidney health—collected between 2006 and 2021 to build detailed distributions by age and sex.

How the New Tool Changes Kidney Disease Detection?

Instead of relying on a single cutoff value, the researchers developed what they call "population-based reference charts" for eGFR, similar to the growth and weight charts pediatricians use to identify children at risk of obesity or undergrowth. "We were inspired by the growth and weight charts used in pediatrics, which intuitively help clinicians identify children at risk of obesity or undergrowth," explains Yuanhang Yang, postdoctoral researcher at Karolinska Institutet. The web-based calculator shows where a patient's kidney function falls within age-based population norms, helping clinicians recognize elevated risk earlier and take preventive steps sooner.

The practical impact is striking. Consider a 55-year-old woman with an eGFR of 80—a value most clinicians would consider normal. However, the new charts show this corresponds to the 10th percentile for women of that age, meaning she has a three-fold higher risk of starting dialysis in the future. This signals an opportunity to act earlier with preventive interventions.

What the Study Revealed About Risk Levels?

The findings highlight critical gaps in current clinical practice. Among people with an eGFR above 60 ml/min/1.73 m² but still below the 25th percentile for their age, only one-fourth had undergone additional testing for urinary albumin—an important test for identifying early kidney damage and guiding timely intervention. The research revealed several key risk patterns:

• Below 25th Percentile Risk: Individuals whose eGFR fell below the 25th percentile for their age faced a much higher risk of progressing to kidney failure requiring dialysis or transplantation.
• Mortality Pattern: The researchers observed a U-shaped pattern for mortality, meaning both unusually low and unusually high eGFR percentiles were linked to an increased risk of death.
• Missed Prevention Opportunities: Many patients with subtly low kidney function for their age never received additional testing that could have identified early kidney damage and enabled preventive treatment.

"For example, consider a 55-year-old woman with an eGFR of 80. Most clinicians would not react to such a seemingly normal value. However, our charts show that this corresponds to the 10th percentile for women of that age, and that she has a three-fold higher risk of starting dialysis in the future. This signals an opportunity to act earlier," says Juan Jesús Carrero, professor at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet.

What This Means for Your Kidney Health?

The research team has made the eGFR distribution charts freely available to healthcare professionals and created an online calculator intended to support clinical decision-making in routine care. This tool represents a significant shift in how kidney disease screening could work in practice. Rather than waiting for obvious signs of kidney damage, doctors can now identify patients at elevated risk based on their age-specific kidney function levels and recommend earlier interventions like additional testing, lifestyle modifications, or medication to slow disease progression.

The study was part of the SCREAM project and received funding from the Swedish Research Council, the Swedish Heart-Lung Foundation, Region Stockholm, and the Swedish Kidney Foundation. For patients concerned about their kidney health, the key takeaway is simple: ask your doctor how your kidney function compares to others your age and sex, not just whether it falls within a general "normal" range. That conversation could make the difference between catching kidney disease early and discovering it only after significant damage has occurred.