Chronic kidney disease in cats – often undetected for a long time

With increasing age, the number of cats suffering from chronic kidney disease (CKD) rises. Between 30 and 40% of all cats over the age of 10 are affected. It often goes unnoticed for a long time. However, the gradual decline in kidney function continues to progress. CKD is one of the most common causes of death in cats and is unfortunately incurable.

INHALT
CNE – what is it? Causes Symptoms Diagnosis and prognosis Treatment Control tests Prophylaxis
CNE – what is it?

CNE is functional or structural damage to the kidneys that has persisted for more than three months. The progressive renal insufficiency that develops over years can lead to kidney failure.

The kidneys act as filters, removing substances that are no longer needed from the body. Each kidney consists of many small filtering units called nephrons. Blood is pumped through the kidneys several hundred times a day, where it is purified. Excess water, toxins, and normal metabolic waste products are excreted by the body in the form of urine. Cats have fewer nephrons than other animals or humans, so their kidney capacity is exhausted more quickly.

In CNE, some of the nephrons are damaged due to various causes. The nephrons that are still active initially increase their performance. The overload causes further nephrons to fail. At a certain point, the kidneys can no longer function adequately. Metabolic waste products accumulate in the body and the regulation of electrolyte and acid-base balance as well as blood pressure are disrupted. The accumulation of toxins in the body leads to uremia (uremia). However, clinical symptoms usually only appear when more than 75% of the nephrons are no longer functioning.

Causes

The cause of CNE is usually unclear, as the trigger may have occurred years ago. The diagnosis is therefore often only made at an advanced stage. Causes include:

  • Kidney inflammation
  • Kidney diseases such as polycystic kidney disease (PKD), amyloidosis, or tumors
  • Ureteral obstruction with urinary flow obstruction
  • Toxins
  • Medications such as NSAIDs (non-steroidal anti-inflammatory drugs/painkillers)
  • High blood pressure
  • Hypercalcemia (= too much calcium in the blood)
  • Lack of oxygen
  • Viruses

Symptoms

The symptoms develop slowly and none are specific to CNE. They also occur in various other diseases. The first signs are polydipsia (increased thirst) and polyuria (increased urination). As the disease progresses, the following symptoms appear:

  • Weight loss, loss of appetite and apathy
  • Nausea and vomiting
  • Dull, matted coat, poor grooming
  • Inflammation of the stomach lining with stomach ulcers, increased salivation, and bad breath
  • Diarrhea
  • Increased blood pressure with damage to the eyes
  • Dehydration
  • Anemia (= lack of red blood cells) with pale mucous membranes and fatigue

Cat drinking water
Diagnosis and prognosis

If your preliminary report indicates a suspicion of CNE, your veterinary practice will first carry out a clinical examination. This is followed by a blood and urine test. In addition, an ultrasound and X-ray examination of the kidneys and abdominal cavity may be useful. Your vet will also measure your cat's blood pressure. This is elevated in 20-65% of cats with CNE. This leads to further damage to the kidneys, eyes, brain, and heart.

In CNE, metabolic waste products accumulate in the blood. At a certain stage of the disease, creatinine, urea, and phosphate levels are elevated. CNE can be diagnosed much earlier using the kidney marker SDMA (symmetric dimethylarginine) in the blood. FGF-23 (= fibroblast growth factor 23) is another biomarker in the blood that indicates an increase in phosphate metabolism in the early stages of the disease. This can be used to decide when a phosphate-lowering diet change is necessary.

Your veterinary practice will measure the urine protein-creatinine ratio (UPC) and the specific gravity of the urine, among other things. CNE causes proteinuria (excessive excretion of protein in the urine).

The severity of CNE and the associated prognosis are classified into four IRIS (International Renal Interest Society) disease stages:

IRIS stage 1: Creatinine is still within the normal range. The filtration capacity of the kidneys begins to decline. No clinical symptoms are noticeable yet.

IRIS stage 2: Creatinine is slightly elevated. About two-thirds of the nephrons are already destroyed. In most cases, the first mild symptoms appear at this stage in the form of polydipsia and polyuria. Some cats are even completely asymptomatic. The average life expectancy is still about three years.

IRIS stage 3: Creatinine is elevated. Approximately 75% of the nephrons are destroyed. The symptoms mentioned above appear. The average life expectancy is approximately two years.

IRIS stage 4: Creatinine is greatly elevated. Approximately 90% of the nephrons are destroyed, leaving only minimal kidney function. The symptoms mentioned above are very pronounced. The average life expectancy is only about five weeks.

Treatment

Unfortunately, CNE cannot be cured. However, various treatment options can improve your cat's quality of life and slow the progression of the disease.

If severe symptoms are already present, your cat must first be stabilized. Your veterinarian will administer an infusion to replenish fluids and balance electrolytes and acid-base levels. You must discontinue any medications that could potentially damage the kidneys.

Depending on the level of the FGF-23 biomarker, but at the latest from IRIS stage 2, you will need to gradually switch your cat to a kidney diet (preferably wet food). Your vet will advise you on this. If your cat does not accept the kidney diet or the phosphate levels remain elevated, you will need to add phosphate binders to their food.

Further treatment depends on the symptoms. Your vet will decide which medications are most important for your cat. They will treat any anemia, proteinuria, or high blood pressure that may occur. Medications for nausea and vomiting may also be necessary. A feverish, bacterial kidney or urinary tract infection is treated with antibiotics. Your vet will draw up a suitable treatment plan for you. They can send the medication for your pet digitally to petsXL. You will then find it in your timeline and can set reminders for yourself.

Control tests

A cat diagnosed with CNE should be taken to the vet for a check-up every one to four weeks at the beginning. Once your cat has stabilised, visits every three to six months are sufficient in the long term.

Prophylaxis

Since CNE often goes undetected for a long time, annual preventive checkups are essential. In addition to a clinical examination, these include blood and urine tests. Ideally, you should start as soon as your cat is fully grown, but no later than seven years of age.

Also, make sure your cat gets enough fluids so that its kidneys can function properly. If it drinks little, you can make the drinking water more palatable by adding a drop of tuna oil. It is also better to feed wet food rather than dry food.