‘Kidney age’, not kidney disease

There should be a rethink in how doctors talk to some patients with reduced kidney health, replacing the term ‘chronic kidney disease’ (CKD) with different bands of kidney age, according to a group of experts writing in the Canadian Medical Association Journal.

From the Universities of Oxford, Bristol and Johannesburg, the researchers argue that for some people a reduced level of kidney function is not necessarily a disease, but a normal and asymptomatic sign of ageing, given the clear link between decreasing kidney health and increasing age.

Since 2002, the different stages of CKD have been used by doctors to label reduced glomerular filtration rate (GFR) – the rate at which blood passes through tiny capillaries in the kidney each minute, but this leads to confusion and worry for some patients.

“Qualitative studies show that communicating a diagnosis of ‘CKD’ to patients can be uncomfortable and unsatisfactory for all concerned, and primary care physicians often face an up-hill battle to retrieve the situation with reassurance,” said lead author Richard Stevens, an Associate Professor at Oxford University’s Nuffield Department of Primary Care Health Sciences.

“Some doctors prefer not to mention the condition to patients so as to avoid any unnecessary worry, given that a reduced but stable kidney function in elderly patients requires regular monitoring rather than immediate intervention.”

CKD stage 5 (where the filtration rate falls below 15 ml/min/1.73m2) is classed as disease at any age, since the kidneys no longer function and dialysis is required.

However, after analysing previously published data from the National Health and Nutrition Examination Survey (2015/16), the researchers argue that CKD up to stage 4 (where GFR declines from 90 to 15 mL/min/1.73m2), does not meet the criteria for disease. Instead they link this with increasing age, from 51 to 95 years old respectively, since this gradual decline in kidney function is not abnormal in older age groups.

When a person’s kidney age is higher than their actual age, the researchers suggest doctors communicate this with discussion of further monitoring and in the context of potential health implications, such as the risk of cardiovascular disease or end-stage renal disease.

Co-author Professor Richard Hobbs, an inner-city Birmingham GP and Head of Oxford University’s Nuffield Department of Primary Care Health Sciences says that applying the same concepts used by doctors to describe heart or vascular age would likely have greater resonance with patients.

“Relabelling CKD stages up to 4 as categories of normal kidney ageing would clear up a common misconception by patients that they require dialysis and transplant due to the use of terms ‘chronic’ and ‘disease’, when their condition is just a normal sign of ageing. For example, a doctor would tell their patient that their kidney age is 68 to 77 years, instead of diagnosing CKD stage 3A.”

The researchers stress that kidney disease remains a significant health concern for many and the term kidney age should only apply to age-related kidney decline. Conditions affecting the kidney such as nephrotic syndrome and polycystic kidneys fall outside the scope of the definition of kidney ageing.

Before a widespread adoption of the kidney ageing terminology by health professionals, the researchers call for further discussion with patient groups and broader studies of kidney decline across different populations and ethnic groups to better understand the link between kidney health and ageing.

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