Chronic Kidney Disease in Cats! What’s the Latest? Chronic kidney disease (CKD) is a common disease in senior cats. Often, by the time of diagnosis of CKD, the etiology is difficult to determine. The causes of CKD in cats may include pyelonephritis, nephrolithiasis, ureteral obstruction with resultant hydronephrosis, tubulointerstitial disease, glomerulonephritis, FIP, neoplasia (usually lymphoma), amyloidosis and polycystic kidney disease. The most common histological finding is tubulointerstitial nephritis of unknown etiology, with an infiltration of lymphocytes and plasma cells and variable degrees of fibrosis. Key points: Look for an underlying cause of the CKD. Kidney palpation, radiology, ultrasound, urine culture and sensitivity are all noninvasive methods. IRIS stage every patient with CKD. Stage 1 cats are not azotemic, but are classified based on whether they have inadequate renal concentrating ability. (USG less than or equal to 1.035) in the absence of rehydration. So yes, you need a urine sample for every patient. Cats need to be rehydrated in order to accurately stage them from Stage 2- Stage 4, using the IRIS CKD guidelines. Blood pressure should be monitored in all senior cats and especially for any cat where CKD is present or suspected. Personal preference is systolic pressure using a Doppler. Obtain a urine via cystocentesis. A complete urinalysis (macroscopic, microscopic and USG) should be included with bloodwork as a minimum data base for all disease screening protocols.

A urine protein/creatinine level should be included on all cats with CRD. A urine culture/sensitivity should be included for all cats with CRD, even with a silent sediment. There is a 22% prevalence of urinary tract infections in cats with CKD. SDMA should be included in my opinion for all cats where renal disease is suspected. SDMA is excreted by the kidneys and it highly correlates with glomerular filtration rate. SDMA increases with an average of 40% loss of kidney function and as little as 25% of kidney function in comparison to creatinine that doesn’t increase until 75% loss of kidney function. SDMA is not impacted by external factors and not impacted by lean body weight. SDMA is a very promising test and is extremely useful to decipher renal function in the muscle wasted feline. It is now included in IRIS staging. A decline in the body condition of a cat with CKD is a negative prognostic indicator. Iris stage of CKD at the time of diagnosis is strongly predictive of survival in cats with CKD. The degree of proteinuria has also been independently related to survival in cats with CKD. Everyone in the audience is well aware of the IRIS CRD staging system. It is a four-level system for staging the continuum of progressive renal disease. It is to be used as a guide in diagnosis, prognosis, and treatment. Staging is based on the level of kidney function as determined by creatinine in the rehydrated patient. Recently, the IRIS CKD Staging recommendations have been updated. When evaluating hypertension, include a retina/fundic examination in all cats.

IRIS STAGING for FELINE CKD Stage 1: Creatinine < 1.6 mg/dl (< 140 mmol/L) = non-azotemic renal disease. Dx in a non-rehydrated state with a less than a normal USG (1.035). Stage 2: Creatinine 1.6–2.8 mg/dl (140–250 mmol/L) = mild renal azotemia Stage 3: Creatinine 2.8–5.0 mg/dl (251–440 mmol/L) = moderate renal azotemia Stage 4: Creatinine > 5.0 mg/dl (> 440 mmol) = severe renal azotemia Sub-staging of Proteinuria

Proteinuria - UPC ratio Non-proteinuric = UPC < 0.2 Borderline proteinuria = UPC 0.25–0.5 - reevaluate after two months Proteinuria = UPC > 0.4

My opinion is to treat the proteinuria earlier than later. If a patient is consistently > than 0.2 in a quiet urine sample, I will begin treatment with an angiotensin converting enzyme inhibitor or an angiotensin receptor blocker.

Substaging by Arterial Blood Pressure

Systolic blood pressure (mm Hg)

Risk of future target organ damage

180

Severe

Severe

Interpreting Blood Concentrations of Symmetric Dimethylarginine (SDMA) in CKD A persistent increase in SDMA above 14 µg/dl suggests reduced renal function and may be a reason to consider a cat with creatinine values 0.4. At our clinic, we tend to initiate treatment earlier using either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Both are well tolerated by the cat.

Hyperphosphatemia Managing hyperphosphatemia in cats with CKD is an important component of therapy and has been linked to survival time. Using a renal diet or a high quality senior diet that is restricted in phosphorus is critical in the early stages of CKD. IRIS treatment guidelines suggest it is ideal to maintain serum phosphate concentrations between 2.7–4.6 mg/dl in stage 1-2, 2.7-5mg/dl in stage 3 and 2.7-6mg/dl in stage 4. The addition of phosphate binders such as aluminum hydroxide needs to be considered when phosphorus is increasing despite dietary restriction. Potassium Supplementation Approximately 20% to 30% of cats with CRF are hypokalemic and as cats with CRD are usually acidotic, the levels present in the blood are likely higher than at the cellular level. This is why you can get clinical signs of hypokalemia, with serum potassium levels in the normal range. The goal of potassium supplementation is to maintain serum potassium concentrations above 4.0 mEq/L (4.0 mmol/L) and usually supplementation with 2meq of potassium gluconate once daily helps to maintain the serum level. Inappetance, Vomiting and Weight Loss Maropitant citrate (CereniaTM) helps decrease vomiting, but it doesn’t increase appetite. Mirtazepine significantly decreases vomiting and increases appetite, activity and weight. We routinely have our patients receive 1/8th of a 15 mg mirtazepine tablet once daily. It has been recently shown that gastric ulceration was not observed in cats with CKD, so it appears there is no benefit in the administration of H2 blockers or gastric protectants. Anemia As CKD progresses, many cats develop anemia due to chronic disease, malnutrition, blood loss and erythropoietin deficiency. Darbepoetin is the current choice for a biosynthetic erythropoietic agent. Iron should be supplemented as well and hypertension is contraindicated and needs to be controlled prior to the administration of the Darbopoetin.