Introduction
Kidney disease is a common condition in cats, especially as they age. It is estimated that up to 30% of cats over 15 years old may have chronic kidney disease (CKD) to some degree [1]. Kidney disease can affect cats of any age, but it tends to be more common in older cats. The kidneys play a vital role in filtering waste products from the blood, regulating hydration and blood pressure, and supporting bone health. When the kidneys begin to fail, toxins can build up in the blood, causing a range of clinical signs. That’s why regular testing is important to detect kidney disease early, before it progresses and causes irreversible damage. With early detection and proper management, many cats with kidney disease can live happily for months to years after diagnosis.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414065/
Blood Tests
There are two main blood tests used to diagnose kidney disease in cats: creatinine and blood urea nitrogen (BUN). Creatinine is a waste product that is filtered out of the blood by healthy kidneys. Elevated creatinine levels indicate impaired kidney function. BUN is also a waste product filtered out by the kidneys. Like creatinine, increased BUN levels signal kidney problems.
Vets will look for persistently high creatinine and BUN levels over multiple tests to confirm chronic kidney disease. Mild to moderate increases may indicate early kidney dysfunction, while substantial increases often correlate with advanced disease. The blood tests also help determine the stage of kidney disease based on levels compared to the normal range. Tracking creatinine and BUN allows vets to monitor progression and response to treatment over time.
In addition to routine blood chemistry, vets may recommend specialized kidney function tests such as glomerular filtration rate (GFR) to precisely assess filtering capabilities. SDMA is a novel biomarker that can detect kidney issues earlier than creatinine. Multiple markers are used together to get the clearest picture of kidney health.
Urine Tests
Urine tests are commonly used to screen for kidney disease in cats. The urinalysis looks at several parameters including urine specific gravity, protein levels, and sediment.
Urine specific gravity measures the concentration of the urine. Kidneys that are not functioning properly fail to concentrate urine adequately, leading to dilute urine with a low specific gravity.
Testing for protein in the urine (proteinuria) helps identify damaged kidneys that are allowing protein to leak into the urine. Persistent proteinuria indicates chronic kidney disease. The urine sediment is also examined microscopically for signs of inflammation, infection, or kidney damage.
Abnormal findings on these urine tests prompt further investigation and can help identify kidney disease in cats.
Blood Pressure
High blood pressure, also known as hypertension, is commonly seen in cats with chronic kidney disease. According to the expert interview at antinolstudies.com, high blood pressure can damage the kidneys by causing added pressure and stress on the blood vessels in the kidneys. This added pressure causes injury that can worsen kidney disease.
Therefore, monitoring blood pressure is an important part of evaluating kidney health in cats. Vets will measure blood pressure during regular checkups for cats with kidney disease. High blood pressure needs to be controlled through medication and diet to prevent further kidney damage.
Imaging
Imaging tests like ultrasounds and x-rays can provide vets with visualization of the kidneys to help diagnose kidney disease. Ultrasound is commonly used to evaluate the size, shape and internal architecture of the kidneys. Small, irregular kidneys may indicate chronic kidney disease. Ultrasounds can also detect masses, stones or obstructions in the kidneys or urinary tract.[1] X-rays allow vets to view the size and shape of the kidneys as well. Mineralization or calculi may also be visible on x-rays. However, ultrasound often provides superior visualization and details of the kidneys compared to radiographs.[2]
[1] https://todaysveterinarypractice.com/hepatology/chronic-kidney-disease-screening-and-confirmation-testing-in-cats/
[2] https://pawsandclawsanimalhospital.com/testing-for-kidney-disease-in-your-dog-or-cat/
Biopsy
A kidney biopsy involves taking small samples of kidney tissue for examination under a microscope. This helps diagnose the specific type of kidney disease and determine the extent of damage to the kidneys. Biopsies are indicated in cats with acute kidney injury or rapidly progressing chronic kidney disease when the cause is unclear. They are performed under anesthesia, either by surgically removing a small piece of kidney tissue (surgical biopsy) or inserting a needle through the skin to extract a sample (needle biopsy). In cats with persistent or uncontrollable vomiting, an ultrasound-guided needle biopsy may be preferred over surgery.
The biopsy samples are sent to a veterinary pathologist who examines them for abnormalities like inflammation, scarring, mineral deposits, or cancer. This helps determine the underlying cause and guide treatment recommendations. Some risks include bleeding, infection, and transient worsening of kidney function. Overall, kidney biopsies provide valuable diagnostic information to optimize management of kidney disease in cats.
Sources:
https://www.youtube.com/watch?v=BLonkj1AixI
Additional Tests
Two other important tests that vets may run to evaluate kidney health are a complete blood count (CBC) and electrolyte panel:
A complete blood count looks at the number, size, and shape of red blood cells, white blood cells, and platelets. Changes in these cell counts can indicate anemia or infection, which are common in cats with kidney disease.
An electrolyte panel measures levels of important minerals in the blood like sodium, potassium, chloride, and bicarbonate. The kidneys help regulate these electrolyte levels, so abnormal results can point to kidney dysfunction.
Staging Kidney Disease
The IRIS (International Renal Interest Society) guidelines provide a standardized system for staging chronic kidney disease (CKD) in cats. IRIS staging is based on two key parameters – blood creatinine levels and urine specific gravity.
There are four stages of CKD according to IRIS guidelines:
- Stage 1 – Blood creatinine less than 1.6 mg/dL and urine specific gravity greater than 1.035
- Stage 2 – Blood creatinine between 1.6 and 2.8 mg/dL
- Stage 3 – Blood creatinine between 2.9 and 5.0 mg/dL
- Stage 4 – Blood creatinine greater than 5.0 mg/dL
Cats are further subclassified as either non-proteinuric or proteinuric within each IRIS stage based on whether they have protein in the urine. Staging helps determine severity, guide treatment options, and estimate prognosis.
According to the IRIS guidelines, SDMA levels can also help identify kidney disease earlier than creatinine alone. SDMA is a biomarker that increases when kidney function is impaired. Persistently high SDMA with normal creatinine may indicate stage 1 or 2 CKD.
IRIS provides a standard staging system for cats with CKD that allows vets to determine where a patient is in the progression of the disease. Staging helps guide clinical decision making and management of CKD.
Ongoing Monitoring
Regular retesting is important to track the progression of kidney disease in cats. Vets will recommend checkups and lab work on a regular basis, such as every 3-6 months. This allows them to monitor trends in kidney values and ensure the cat’s treatment plan is effective. Some key parameters vets monitor include:
- Blood creatinine and BUN levels – to assess kidney function
- Phosphorus and calcium levels – which can become abnormal as kidney disease progresses
- Blood pressure – hypertension is a common complication
- Urine specific gravity – to evaluate concentrating ability
- Weight and muscle mass – signs of wasting may occur
The frequency of retesting depends on the stage of kidney disease and overall stability of the cat. More advanced kidney disease requires closer monitoring. Vets may also recommend periodic imaging, like ultrasound, to check kidney size and shape over time. Tracking kidney disease helps provide the best care as it progresses.
Conclusion
There are several different tests vets use to diagnose kidney disease in cats. The most common initial tests are blood and urine tests, which can detect elevated levels of waste products like creatinine and BUN that indicate impaired kidney function. Vets may also check blood pressure, take images of the kidneys, or do a kidney biopsy to evaluate kidney structure and look for damage.
Based on all the test results, vets will determine the stage of kidney disease and whether there are any accompanying conditions that need treatment. Ongoing monitoring with blood and urine tests allows vets to track the progression of kidney disease over time. With early detection from regular senior wellness checkups, kidney disease can often be well-managed with a combination of medications, diet modification, and IV fluids.