Chronic Kidney Disease (CKD) in Cats
Chronic kidney disease (CKD) is an incurable disease that progresses over months and years, mainly in older cats, and is the most common cause of death in old cats.
Polzin (2011) defines chronic kidney disease (CKD) as ‘any structural and/or functional abnormality of one or both kidneys that has been continuously present for three months or longer.’. This definition covers a broad range of CKD manifestations and causes, meaning that the condition can present in many different ways.
Chronic kidney disease is characterised by a progressive reduction in the number of nephrons, the functional units of the kidney. Even if the cat’s kidneys have over 200,000 nephrons, these cannot grow back once they have been damaged. If fewer nephrons are available, kidney performance decreases and renal insufficiency occurs (chronic renal insufficiency = CRI). The deteriorated nephrons are remodelled into scar tissue by inflammatory processes (= immune processes). Scar tissue is non-functional. If the number of functional nephrons continues to decrease, more and more scar tissue develops, which leads to a poor prognosis. This leads to renal fibrosis, which reduces the size of the kidneys. In the course of CKD, the kidneys can therefore shrink or enlarge significantly, depending on the cause.
The nephrons are responsible for controlling the composition of the urine. This involves the targeted excretion of superfluous and urinary substances such as toxins, metabolic end products (e.g. creatinine) and excess minerals (e.g. phosphate). Water is recovered as well as necessary substances. In CKD, the remaining nephrons cannot adequately take over the tasks of the nephrons that have already disintegrated, so that toxins build up in the blood. The increasing accumulation of urinary substances in the blood (= uraemia) leads to urinary intoxication and clinical symptoms.
In addition, the cats become dehydrated because not enough water can be recovered in the nephrons. The kidneys are involved in a number of processes in the body that are affected by CKD. There are some self-reinforcing processes that promote the progression of CKD.
Clinical symptoms are only noticed when about 2/3 to 3/4 of the nephrons are destroyed. This also explains why many cats with CKD are presented late at the vet’s practice.
Causes and risk groups
The underlying causes of chronic kidney disease often remain unclear. Inflammatory processes in the kidneys are a possible cause. Many cats have chronic tubulointerstitial nephritis (= a long-lasting inflammation of the kidneys that affects the kidney tissue, in particular the renal tubules (tubules) and the surrounding tissue (interstitium)). This inflammation can progress over years and lead to damage and scarring (fibrosis) of the kidney tissue. Causes of such damage include toxic damage (toxins, certain drugs that damage the kidneys), lack of oxygen (hypoxia), e.g. during anaesthesia, chronic pyelonephritis, urinary stones, viral infections (retroviruses, morbilliviruses), chronic glomerulonephritis (= long-term, inflammatory disease of the renal corpuscles (glomeruli), which leads to progressive damage to kidney function).
Other causes are amyloidosis (= deposition of immunoglobulin chains in organs such as the kidneys), polycystic kidney disease (= hereditary cyst formation in the kidneys), kidney tumours, mineral disorders in which the kidneys calcify (= renal calcinosis) and congenital disorders associated with certain breeds.
In fact, European shorthair cats are most frequently affected. However, this is due to their distribution. There are breeds that are said to be prone to CKD. These include Main Coon, Burmese, Siamese, Russian Blue, Abyssinian.
Chronic kidney disease in cats (CKD) occurs in 10-30% of cats over the age of 10. In cats over 15 years of age, one in two or three is affected by CKD. As early as 7 years of age, the first signs of the onset are usually found – such as an individually elevated creatinine value or a slightly elevated SDMA value.
As there is no cure, and early diagnosis is the only way to ensure a longer and better cat life. Targeted management can slow down the progression of CKD and improve the cat’s quality of life. It therefore makes sense to carry out at least annual health checks with blood tests in cats from the age of 7 in order to identify CKD at an early stage.
