A blood test that comes back inside the "normal" range can still be an early warning sign that your kidneys are in trouble. That is the message from researchers at Karolinska Institutet, whose new study in Kidney International argues that the standard reference values doctors rely on are too blunt to catch declining kidney function early.
The team built age- and sex-specific reference charts from nearly seven million kidney test results collected in the Stockholm region between 2006 and 2021, covering more than 1.1 million adults aged 40 to 100. Their finding: what counts as "normal" for a 40-year-old is often abnormally low for a 55-year-old, and clinicians are missing that signal.
Why the age of your kidneys matters
The test in question is eGFR, or estimated glomerular filtration rate, a blood-based measure of how well the kidneys filter waste. Under current guidelines, an eGFR above 60 is generally considered normal and rarely triggers follow-up. The Karolinska team says that threshold hides real risk.
Their charts, published online on January 16, 2026 in Kidney International, show that people whose eGFR falls in the bottom quarter for their age had a markedly higher risk of eventually needing dialysis or a kidney transplant, even when the raw number looked fine.
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"We were inspired by the growth and weight charts used in paediatrics, which intuitively help clinicians identify children at risk of obesity or undergrowth," said Yuanhang Yang, a postdoctoral researcher at Karolinska Institutet and first author of the study.
The 55-year-old example
To make the point concrete, senior author Juan Jesús Carrero, professor at Karolinska Institutet, offered a scenario. "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," Carrero said.
The researchers also flagged a practical gap. Among patients whose eGFR was above 60 but below the 25th percentile for their age, only about one in four received a follow-up urine albumin test, the second key measurement used to detect early kidney damage.
To help doctors act on the new percentiles, PhD student Antoine Creon built a free online eGFR percentile calculator that shows where a patient's value sits compared with peers of the same age and sex.
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A largely silent disease
The stakes are high because kidney disease is easy to miss until it is advanced. Chronic kidney disease affects more than 1 in 7 US adults, roughly 35.5 million people, and as many as 9 in 10 of them do not know they have it, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
Standard testing relies on two numbers. eGFR is calculated from a blood draw and estimates filtering capacity. The urine albumin-to-creatinine ratio, or uACR, checks whether protein is leaking into the urine, an early sign that the kidney's filters are damaged.
Symptoms worth mentioning to your doctor
Because early kidney disease is usually silent, symptoms tend to appear late. The National Kidney Foundation lists several early signs worth flagging, including foamy or bubbly urine, which can indicate protein leakage, along with swelling in the ankles, feet or around the eyes, and persistent fatigue that does not improve with rest.
Anyone with diabetes, high blood pressure, heart disease or a family history of kidney problems is at higher risk and should ask their doctor whether their eGFR and uACR results have been checked, and how those numbers compare with what is typical for their age.
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