Age-adapted CKD definition would reduce burden of disease, INS told

Chronic kidney disease (CKD) is a key driver of morbidity in Ireland, but the prevalence of the disease may be overstated, heard the recent Irish Nephrology Society (INS) Winter Scientific Meeting in Galway. 

Prof Austin Stack, Consultant Nephrologist, University of Limerick, gave a talk on the burden of CKD in Ireland. He said that an age-adapted CKD definition would reduce the burden of the disease in Ireland and the downstream impact on health utilisation.

“Depending on our equation and definition of CKD, there is variability in the burden of CKD in this country,” he said.

Some decline in kidney function was normal as people aged and may not always be an indication of kidney disease. An age-adapted definition appeared to be a valid construct and would “certainly reduce the burden of CKD in Ireland”.

“It is something that we should look at,” commented Prof Stack. “It’ll have an important impact on the number of referrals we get. Because when we get referrals to our clinic, we really only want to get people who we can do something for, in terms of modifying their risk of progression and managing complications…. We actually could reduce the burden of CKD in Ireland today with the stroke of a pen if we adapted this definition.”

‘Rethink’

Prof Stack told delegates that CKD costs the State at least €427 million annually, with an average length of stay of 12 days – “above and beyond” what is seen internationally. In 2022, one-in-eight hospitalisations were due to the disease and one-in-five deaths had CKD as a diagnosis.

Prof Stack said he wished to rethink and reexamine the evidence for determining the “true” burden of kidney disease in Ireland.

He asked how nephrologists were going to manage the burden of CKD in 2025 and beyond. He said that everyone in the specialty would agree that their clinics were very busy.

“Our job at the INS is to try and inform clinical practice,” he said. 

In recent years referrals from GPs to nephrology departments have increased significantly, with approximately 11,000 last year.

“The challenge is these numbers will continue to increase unless we do something about it,” he said.

“Is there a need to change how we define kidney disease and perhaps influence our management on a day-to-day basis?” he asked.

In the past decade, nephrologists had learned a lot more about CKD in Ireland. There have been major reports published, including by The Irish Longitudinal Study on Ageing (TILDA), which have provided an insight into the burden, distribution, and incidence of CKD.

Referencing the rising prevalence in Ireland, he said: “Is it all the diabetes, the hypertension, the lifestyle, or is it just that people are living longer?” Prof Stack noted that the older the population, the greater the prevalence of CKD.

“It is an age-dependent phenomena,” Prof Stack continued. “But if you look at the trends over time, the prevalence for most of the age groups is fairly static, with the exception of the older age group. So the big driving force appears – at least from this analysis – to be age.”

Currently, there were a number of equations to estimate kidney function, “10 at least”, according to Prof Stack.

“So if we apply those to a standardised population, you and I would think that we should get pretty much the same value or very close together.”

However, “if we apply that to the TILDA population [which looked at people over the age of 50] the prevalence can be as high as 18 per cent or as low as 7.5 per cent…. You have to ask yourself what is the correct estimate of the burden. Based on these equations, I am unclear of how common CKD is in our country…. Our equations provide different estimates of the burden in the population. They also do not account for individuals living longer as well as older individuals.”

Prof Stack highlighted that reduced kidney function was a normal part of ageing and was not necessarily reflective of kidney disease.

“So somewhere that message has gotten lost in the wider community,” he said. “We do know and there is good evidence to show that kidney function is not stable throughout the lifespan; that there is a normal physiological decline.”

We do know and there is good evidence to show that kidney function is
not stable throughout the lifespan; that there is a normal physiological decline

When a fixed threshold was used to define kidney disease, normal physiological ageing was ignored, outlined Prof Stack.

“Anything less than 60 (in eGFR), regardless of their age, is defined as having CKD. So particularly individuals above the age of 55 to 60, who have normal kidney function according to normal ageing, are potentially misclassified as having chronic kidney disease.

“So it is very likely that the increasing burden of chronic kidney disease may in part – may in a large part – be attributed to people living longer in this country.”

Prof Stack said that there have been calls for an age-adapted formula, which would mimic the normal decline in kidney function.

“But the next important question is the relationship between GFR and adverse outcomes should follow a similar pattern. In other words, the relationship between GFR and death and GFR and dialysis should also vary by age. Because what we don’t want to do is miss individuals in this group who might have a higher risk of dialysis or death.”

Speaking during a questions and answers session, Prof Stack said that some older patients – a population that was increasing year on year – were being misclassified as having CKD. This was resulting in an increased burden on nephrology clinics.

However, he reiterated: “We need to be sure that those individuals, where we are using an age-adapted threshold, don’t have kidney disease.” Prof Stack added that there needed to be debate, discussion, and consensus before any change was made.

“Sometimes I think, do we have to wait for international partners to move first or can we be the first? I do think that if the evidence is good – that’s why we need the debate – I think we can make the decision.”