For decades, doctors around the world, including in India, have relied on the same set of numbers to decide whether someone's kidneys are working normally. These numbers, known as reference ranges, were built almost entirely from studies conducted on European and American populations. A new study published in the American Journal of Kidney Diseases in 2026, led by researchers at the Postgraduate Institute of Medical Education and Research (PGIMER) in Chandigarh, along with collaborators from institutions across India, Belgium, France, the United States, and Singapore, has now put that assumption to the test. What they found suggests that a substantial number of healthy Indians may be getting measured against a yardstick that was never built for them.

First, What Is GFR and Why Does It Matter?

To understand why this study matters, it helps to understand what is actually being measured. The glomerular filtration rate, or GFR, is essentially a measure of how efficiently the kidneys filter waste out of the blood. Every kidney contains millions of tiny filtering units, and GFR tells you, in effect, how many litres of blood these filters can clean every minute. It is the single most widely used number in medicine for judging kidney health. A low GFR usually signals that the kidneys are struggling, while a number within the expected range is generally taken as reassurance that everything is working as it should.

The trouble is that the "expected range" doctors have been using was set decades ago, largely from research done on populations in Europe and North America, and then applied more or less unchanged to patients everywhere else in the world, including India.

A Study Designed to Ask a Simple but Important Question

The research team set out to answer a deceptively simple question: what does a normal GFR actually look like in a healthy Indian adult? To find out, they enrolled 592 adults from Chandigarh who had no known kidney disease, drawing participants both from the general population and from individuals being evaluated as prospective kidney donors, a group that is typically in excellent health since donor eligibility already requires it.

What makes this study particularly rigorous is the method used to measure kidney function. Rather than relying on an estimated GFR, calculated indirectly from a blood test using a mathematical formula, the researchers measured GFR directly, using a technique involving a substance called iohexol that is injected into the bloodstream and tracked as it clears out through the kidneys. This is widely considered the gold standard for measuring kidney function, far more accurate than the estimation formulas used in routine clinical practice, though also far more resource-intensive, which is exactly why it is rarely used outside of research settings.

The Findings: A Noticeably Lower Baseline

The results were striking. The median measured GFR among these healthy Indian adults came out to 82 millilitres per minute, once adjusted for body size. For context, the equivalent figure typically reported in European populations is closer to 107. That is not a small gap. Even among the youngest and presumably healthiest participants in the study, those under 30, the median GFR was 98, still meaningfully below the European baseline used for comparison.

The study also confirmed a pattern that will be familiar to anyone who has read about ageing and organ function before: GFR declines gradually as people get older. It moved from around 98 in adults under 30, down to 91 in their thirties, 85 in their forties, 77 in their fifties, and 73 past the age of 60. Men in the study had somewhat higher GFR than women on average, though the difference was modest. Importantly, the researchers checked whether these lower numbers might simply be an artefact of who they happened to enrol, testing for differences by body mass index and by whether someone came from the general population or was a prospective kidney donor, and the pattern held steady across all these groups.

Perhaps the most practically important finding in the entire study concerns the everyday blood test most people actually receive. In routine clinical care, almost nobody gets their GFR measured directly using iohexol. Instead, doctors estimate it using a formula based on a blood marker called creatinine. When the researchers compared this estimated GFR against the true, directly measured GFR of their participants, they found that the creatinine-based formula overestimated kidney function by an average of 24 millilitres per minute, a very large margin in clinical terms. A second estimation method based on a different blood marker, cystatin C, came far closer to the true measured value, off by only about 1 millilitre per minute on average.

In plain terms, a routine blood test using the standard formula could tell an Indian patient their kidneys are working better than they actually are, by a wide margin. Someone whose kidneys are genuinely beginning to decline might still receive a result that looks comfortably normal.

Why Might This Be Happening?

The researchers were careful not to overstate their certainty about the exact cause, but pointed to a few plausible contributing factors: genetic differences between populations, variations in diet and protein intake, differences in typical body composition and muscle mass, and environmental factors such as pollution or the burden of certain infections common in India. Notably, this is not an isolated finding unique to India. The researchers noted that a similar pattern, where creatinine-based formulas overestimate true kidney function, has also been observed in African, Hispanic, Japanese, and Chinese populations, suggesting this may be a broader issue affecting much of the world outside the original European and American populations these formulas were built on.

The authors were also transparent about the limits of their work. Their participants were drawn specifically from Chandigarh and the surrounding region in North India, so the findings may not automatically apply to India's many other ethnic, dietary, and geographic communities. Older adults above 65 were also underrepresented. The researchers were clear that their findings need validation in more diverse groups before any change to clinical thresholds, and called for future studies testing how these locally calibrated numbers relate to actual health outcomes, not just to healthy volunteers.

A Bigger Question This Study Raises

Taken as a whole, this study makes a compelling case that "normal" is not a universal number. It changes depending on the population you are looking at, and applying a threshold built for one group of people onto an entirely different population risks two kinds of mistakes: telling healthy people they might have a problem when they do not, and, arguably more worryingly, reassuring people that everything is fine when their kidney function may already be quietly declining.

This raises an obvious follow-up question, one this study does not answer but that deserves serious attention. GFR is not the only measurement used to assess kidney health. Alongside it sits another crucial marker called the urine albumin-to-creatinine ratio, or uACR, and if population-specific reference ranges matter this much for GFR, there is little reason to believe uACR would be any different.

Why uACR Deserves the Same Scrutiny, Perhaps Even More Urgently

uACR works by measuring tiny amounts of a protein called albumin that leak into the urine when the kidneys' filtering units are damaged. Under normal circumstances, very little albumin should pass through into urine at all. When kidney filters begin to sustain damage, even damage too subtle to affect the overall GFR yet, albumin starts leaking through in small but detectable amounts. This makes uACR one of the earliest available warning signs of kidney trouble, often showing up years before GFR itself starts to fall. Major international kidney guidelines already recognise this, recommending that uACR be measured alongside GFR, not as an afterthought, precisely because it can catch problems earlier.

And yet, the normal reference values used for interpreting uACR results in Indian patients today are, just like GFR once was, borrowed almost entirely from Western populations, without the kind of large, rigorous, population-specific validation this new GFR study has just provided. If diet, muscle mass, genetics, and environmental exposure can meaningfully shift what a normal GFR looks like in India, as this study suggests, it is entirely reasonable to expect that these same factors could shift what counts as a normal amount of albumin in urine as well. Muscle mass in particular directly affects the creatinine part of this ratio, and dietary protein intake, both of which this Chandigarh study already showed differ from Western populations, could easily influence how uACR results should be interpreted here.

There is also a practical argument for prioritising this research, arguably an even stronger one than for GFR itself. Measuring true GFR the way this study did, using injected iohexol, is accurate but complicated, expensive, and simply impossible to do on a large scale in everyday healthcare settings. uACR, by contrast, only requires a small urine sample and can increasingly be tested using simple, affordable point-of-care devices right at a primary health centre or during a community screening drive, without needing to send samples to a distant, well-equipped laboratory. This is precisely the kind of tool that platforms like Prantae Solutions' Proflo-U were built around, bringing accurate, lab-grade uACR testing to the frontline of care itself. That accessibility is exactly why uACR has the potential to reach far more people, far earlier in the course of disease, than GFR measurement ever practically could. If that is the tool most likely to actually get into the hands of frontline health workers and community screening programmes across the country, then getting its reference ranges right for the Indian population is not a secondary concern. It is arguably the more urgent one.

A Measurement Problem, Not Just a Medical One

What this study ultimately reveals is not that Indian kidneys are somehow weaker or more prone to disease. It reveals something more fundamental: that the yardsticks used to judge health were never built with everyone in mind, and that this gap has likely gone unnoticed for years simply because nobody had gathered the data to see it. Fixing this is not just an academic exercise. It is the difference between catching kidney disease early enough to change its course, and discovering it only once the damage can no longer be undone. If Indian researchers now have the evidence to say GFR needs its own local benchmark, the next, arguably more urgent, task is making sure the earliest warning sign of all, uACR, gets the very same careful, homegrown attention.

Source: Yadav AK, Kaur J, Kaur R, et al. Distribution of GFR in Apparently Healthy Indians. American Journal of Kidney Diseases (2026). DOI: 10.1053/j.ajkd.2026.03.050