Chronic kidney disease needs to be redefined

Although a variety of conditions and syndromes may affect the kidneys over either chronic or acute time frames, the term “chronic kidney disease” (CKD) is used to describe a decrease in the filtration ability of the glomerular capillaries in the kidney. The most prevalent forms of CKD in healthcare systems are typically the asymptomatic stages conventionally termed CKD stages 4 or below. Dr Benjamin Smart, senior lecturer at UJ, and Dr Richard Stevens and his colleagues at The Nuffield Institute for Health Research (NIHR) School for Primary Care Research, University of Oxford, questioned whether early-stage CKD is a genuine disease.

Specific dysfunctions

In 2002, the US National Kidney Foundation proposed that the term “chronic kidney disease” be applied for specific dysfunctions of the kidneys, defined primarily by the glomerular filtration rate. These guidelines proposed that glomerular filtration rate less than 60 mL/min/1.73m² be considered CKD stage 3; glomerular filtration rate less than 30 mL/min/1.73m² considered CKD stage 4; and less than 15 mL/min/1.73m² considered CKD stage 5, with earlier stages 1,2 dependent on other evidence of kidney damage, such as proteinuria.

In JECP, Smart, Stevens and Verbakel explain how “whether a condition is labelled a disease matters. All analyses of the concept of disease [seem to] include either reference to subnormal part function, some form of “harm” criterion, or both, so… being diagnosed with a disease has psychological consequences. Although causing patients distress in this way is necessary when the patient is truly sick, misclassifying as disease a condition such as stage 3 CKD in older adults is [harmful]”.

The researchers reviewed four prominent definitions of disease in the philosophy of medicine literature. In CMAJ, Stevens et al explain that they “considered whether CKD, defined by current thresholds for glomerular filtration rate, is disease according to these definitions. [They] found that CKD stage 5 was disease by any definition, because it is associated with harm and is statistically uncommon in any age group. However, earlier stages of CKD are associated with harm as risk factors for further disease (renal or cardiovascular) rather than as disease itself, and whether they are statistically abnormal depends entirely on age”.

Kidney age classification

The researchers suggest that the CKD “stage” system of classification should be replaced with a “kidney age” system similar to the “heart age” system often employed in cardiology. They stress, however, 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). Ultimately they “hypothesize that adjusting terminology would in many cases avoid unnecessary anxiety, while still signalling concern where appropriate [because] patients will (as some already do) understand the decline as a natural aging process”.

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.