When diagnosing and monitoring a cat with kidney disease, your vet may want to do various tests. Most of these are not invasive and do not cause your cat any discomfort. These tests will help your vet determine the severity of the problem and the best treatment options to keep your cat as healthy and happy as possible for as long as possible. Hopefully this information will help you to understand why your vet is advising various tests and how the results can help your cat.
Blood tests are very important for diagnosing kidney disease and there are various different results which are important.
Urea is a waste product formed when protein is digested. It is excreted in the urine. It is increased in cats with kidney disease, however it can also be increased due to other reasons such as heart disease, dehydration, an abnormally high level of protein in the food or where muscle is being broken down due to other illnesses. On it’s own, it is not a very useful test of kidney function but it is when used in combination with other tests such as creatinine.
Creatinine is also a waste product of food and also excreted in the urine. It is a much better indicator of kidney function and is increased in cats with kidney disease. It may also be increased in dehydrated cats. The creatinine level is used to determine the IRIS stage of disease. Creatinine doesn’t tend to increase until at least 75% of kidney function is lost.
SDMA is a more recent marker of kidney function which starts to increase much earlier than creatinine (when around 25% of kidney function is lost). It is also less affected by other body systems. It allows kidney disease to be detected much earlier than previously possible.
Phosphorus is a mineral found in food which performs a lot of important roles in the body, including calcium balance. Having the right amount is really important as too much can be dangerous. The kidneys excrete phophorus but less effectively with kidney disease, therefore the levels in the blood stream increase. Increased levels of phosphorus are toxic to the kidney, so make the problem worse. It therefore becomes a vicious cycle and decreasing the amount of phosphorus in the diet to try and keep the phosphate level low is critical to maintain kidney health.
Red blood cell count/PCV/Haematocrit
Anaemia is common in later stages of kidney disease and can cause fatigue and a feeling of illness. Regular monitoring of the red blood cell level in the blood will help to detect this problem before it gets severe, and enable treatment when needed.
Collecting a urine sample from your cat doesn’t have to be difficult. You can either collect a sample using a litter tray and special non-absorbent cat litter, or your vet can get a sample directly from the bladder (this is the best way if sending for culture as there is less risk of contamination).
Urine specific gravity (USG)
The USG measures the concentration of the urine. In healthy cats, this is normally very high (over 1.035). In cats with kidney disease, it will be less than this. The USG is used in combination with the urea and creatinine. If all values are high, the cat is dehydrated. If the USG is low and the urea and creatinine are high, this indicates that the kidneys are not functioning correctly.
Urine protein:creatinine ratio (UPCR)
As kidney disease progresses, the filter within the kidney becomes more leaky and allows protein, which is normally kept in the blood stream, to enter the urine. Protein in the urine has been shown to be a worse prognosis in cats with kidney disease. Medication to reduce the blood pressure within the kidney can help to reduce the amount of protein being lost in this way.
Because the urine is more dilute, cats with kidney failure are more prone to urinary tract infections. The bacteria in these infections can then enter the kidneys and make the problem worse. Culturing the urine will allow your vet to know if antibiotics are needed, and which ones will target the bacteria present.
Blood pressure measurement
Cats with kidney disease are more prone to having high blood pressure, and high blood pressure can cause a worsening of kidney disease itself, another vicious cycle. High blood pressure can also cause other serious problems such as blindness and strokes. Regular monitoring of your cat’s blood pressure is really important to prevent these often irreversible problems from happening. Lowering the blood pressure with medication is simple and effective.