The linear classification into four progressive stages of chronic kidney disease in cats (and dogs) is done by IRIS (International Renal Interest Society). The individual stage defines the severity of the chronic kidney disease ( CKD) and is associated with the cats prognosis, too.
IRIS recommends certain treatments and procedures as well as therapy for the cat in the second stage. A further distinction is made between staging= Classification of the cat into a stage of chronic kidney disease according to IRIS... before and after treatment. A cat may be considered to be in a later stage before treatment and then ideally ” returns” to an earlier stage within treatment. However, the degree of kidney damage is not improved because CKD is irreversible. In fact, only the blood and urine analyses show levels of an earlier stage. This can improve the prognosis and is usually associated with a better quality of life for the cat.
Stage two behind the scenes
In the second stage, kidney function is already reduced by 2/3. Urinary substances can no longer be completely excreted and start to accumulate in the blood.
Reduced renal excretion already leads to changes in the blood count. In stage two, slightly increased creatinineCreatinine is a breakdown product of muscle metabolism. Its blood level is dependent, among many factors, on age, weight, nutritional status and muscle mass. Hence, creatinine levels in the blood vary from individual to individual. Creatinine is continuously excreted in the urine. Increased blood creatinine... blood levels become noticeable. Creatinine has a value of 140-250 μmol/l or 1.6-2.8 mg/dl in this stage and can thus still be within the upper standard range.
Compared to past check-ups, however, it becomes obvious that the creatinine values are now increasing and are no longer within the individual reference range of the cat. If at least annual kidney check-ups have been done from the age of five, an individual reference range for the own cat is recognised. Every cat has very different creatinine values depending on its muscle mass, age, feeding, breed and many more aspects. The aim is to detect a creatinine increase very early. Since the increase itself is the sign of impaired kidney function and not the exceeding of an upper threshold of normal range set by the laboratory.
The SDMASDMA = Symmetrical Dimethylarginine, which is a degradation product of the amino acid arginine and is excreted solely through the kidneys. SDMA is a highly specific biomarker for kidney function in cats. Read more: SDMA test (blood test)... value, which rises earlier than the creatinine blood value, can also be of help in this regard. In the second stage of CKD, the SDMA concentration in the blood is 18-25 μg/dl and thereby slightly elevated as well.
Urine analysis usually shows a UPC value (urine protein-to-creatinine ratio) above 0.4, which according to IRIS represents proteinuriaIncreased protein in urine, leading to loss of protein. Normally, only a very small amount of protein is excreted in the urine. In chronic kidney disease, the amount lost may increase. High blood pressure damages blood vessels in the nephrons making them more permeable and... (= loss of proteins in the urine).
Clinical symptoms are still minor. Lack of appetite, sleepiness and increased drinking (polydipsiaExcessive thirst due to illness, leading to excessive production of urine (polyuria)....) and frequent peeing (polyuriaExcessive production of urine, potentially due to kidney failure....) as well as weight loss may be noticed more frequently.
second stage measures
The focus is on slowing down the progression of CKD. This includes controlling the cat’s blood pressure. If blood pressure is elevated, it should be lowered with medication. About 20 % of cats show hypertensionHigh blood pressure. in the early stages of CKD. There are two types of blood pressure: One is the systemic blood pressure. Only this can be measured in the cat. The systemic blood pressure is divided into sub-stages by IRIS, because high blood pressure can lead to organ damage (e.g. in brain, kidneys, or retinal detachment). The particular sub-stages indicate the respective risk of organ damage.
In addition, there is the blood pressure in the kidneys themselves, especially in the renal corpuscles. This is regulated independently by the kidneys themselves. The blood pressure in the kidneys is important so that sufficient urinary substances (such as creatinine, SDMA, ureaUrea is the nitrogen-containing breakdown product of protein metabolism. The nitrogen from the proteins is converted to ammonia in the liver, which is combined with carbon dioxide to form urea. This is continuously excreted via the kidneys but also via sweat. Urea is one of...) are “squeezed out” of the blood into the urine. The latter renal blood pressure thus supports the kidney function. Whereas a good systemic blood pressure is important for the cat’s well-being in general.
For example, low blood pressure leads to fatigue, sleepiness and a wobbly (so-called plantigrade) gait. Too high blood pressure, on the other hand, can be harmful to the cat and its kidneys, too. Therefore, blood pressure monitoring is advisable when using antihypertensive medication.
IRIS also recommends that in stage 2, the phosphate level in the blood should be controlled and kept below 1.5 mmol/l. This can be achieved by changing the feed to protein and phosphate-reduced diets and/or by using phosphate binders.
All has not been sad or done
According to literature, the average survival time of cats in stage 2 is over 3 years. This is a fairly long and hence comforting period of time to begin with, referring to an old cat. Stage two should therefore be maintained for as long as possible. Stabilising this stage is thus the focus of veterinary efforts. This is achieved by slowing down the progression of CKD by addressing the vicious circles of its further development. It requires not only a good diagnosis but also an overview of the cat’s overall condition (clarification of possible comorbidities, i.e. additional diseases) and its kidneys (possible other diseases?).
The progression in the cat is not linear, but gradual, making it appear to the cat owner as if there is an abrupt decline. This is not uncommon with insidious symptoms. At some point they will be obvious and noticeable to the owner. Then they will begin to recognise other symptoms. If there is a worsening, a veterinarian should be consulted and the staging should be done again.
Perhaps, despite therapy, the journey will then continue towards stage 3, which will be presented in the next blog article.
- Sparks, A. H. / Caney, S. / Elliot, J. / Finch, N. / Gajanayake, I. / Langston, C./ Lefebvre, H. / White, J. & Quimby, J. (2016): ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. Journal of Feline Medicine and Surgery,18, S. 219–239.
- IRIS-Staging: http://www.iris-kidney.com/pdf/IRIS_Staging_of_CKD_modified_2019.pdf