Clinical approach and evaluation of Renal disease (CKD and AKI) in cats and the concurrent diseases: Feline Hyperthyroidism (FHT)

The function of the kidneys is to regulate the volume and the composition of the extracellular fluid by the formation of urine.

What are the kidneys?

They are nothing more than filters that selectively are keeping certain compounds in the blood, allowing the unnecessary waste products to escape into the urine. This is achieved by formation of an ultrafiltrate of plasma by the passage of solutes, small proteins and other non-cellular constituents of the blood across the glomerular filtration. Following filtration, the composition of this fluid is altered according to the physiological needs of the animal by the secretion and reabsorption of solutes and water as it passes along the nephron (the nephron being the microscopic structural and functional unit of the kidney). In a healthy animal, under normal physiological conditions, less than 1% of the fluid that is filtered by the kidney will be eventually excreted as urine. During aging filtration process cause to become progressively less active, blood flow to the kidneys increases in an attempt to improve filtration, this is the reason why cats that having kidney failure urinate more frequently.
Kidney disease can influence these processes in a number of different ways: most frequently kidney disease is diagnosed when glomerular filtration rate is decreased (recognized usually as azotemia) in a patient either with chronic kidney disease (CKD) or acute kidney injury (AKI).
Owners of patients with CKD will usually report that their animal is drinking and urinating more than normal. Reduction of appetite or weight loss may be reported in patients with renal disease. Signs referable to systemic hypertension (mydriasis , hyphema , blindness) might be reported by the owners with cats with CKD. Occasionally, there are two symptoms that can be seen when anemia of renal failure develops and this are, ulcer from the mouth can be present and heart murmur can be detected.
Thus, the most common clinical signs of kidney failure include both symptoms, increased water consumption that we called (polydipsia) and increased urine production called (polyuria).
There are various clinical studies where they have evaluated the prevalence of renal failure in cats. For most cats, first clinical signs begin anywhere from the age of 7 to 12 years. However, One study found that approximately 49% of cats age 15 years and older had some degree of chronic renal failure.

The chronic renal failure of CKD is called technically chronic tubuli-interstitial nephritis, a term that describes a microscopic finding and is not specific for a particular cause. A specific cause for renal failure cannot be determined in most of the cats. In most of the cat’s kidney failure is the end result of several insults or diseases to the kidneys, over a prolonged period of time.

There are four main factors identified, that may hasten the progression of the renal disease:
HYPERTHYROIDISM (over activate thyroid glands) –

FHT (feline hyperthyroidism ) is a disease of middle-aged cats with no clear breed or sex predisposition. The clinical signs of FHT are variable, reflecting the generalized and multisystemic nature of the disease.
Common clinical signs include weight loss, increased appetite, hyperactivity, vomiting, diarrhea, polyuria/polydipsia, poor grooming, and behavioral changes. Any combination of clinical signs and varying degrees of severity are common. Weight loss is the most common sign of FHT. Afflicted cats are often in poor body condition and have a generally unkempt appearance. Despite their age, cats with FHT appear hyperactive, aggressive and exhibit signs of anxiety. Impaired stress tolerance and panting are common. The hyperthyroid cats are in general hypertensive (they have high blood pressure), and this leads to increased blood flow through the kidneys. As it was mentioned above, the extra blood flow helps the aging kidney to maintain their function. With an adequate treatment for hyperthyroidism, the blood pressure normalizes and the extra blood flow to the kidneys is no longer present. This can lead to a sudden decompensating of the kidneys with already marginal function.
Long term intake of acidified diet: diets that are used to make urine pH more acidic are very common. Those diets are useful for managing certain bladder problems in cats, some bladder problems more common in young adult cats, but they are potentially very harmful to the kidney of older cats. These diets cause chronic loss of potassium from the body. Chronic low potassium has been identified as a significant factor in the progression of kidney diseases in older cats.

Urinary tract infections:

the bacterial infections in the bladder and/or in the kidneys may be present without any apparent signs. The bacteria can damage the kidneys, therefore for the cats with kidney diseases, their urine should be checked for the presence of opportunistic bacteria. The most accurate way to detect bacterial infection is to have a bacterial culture of the urine.
Nephroliths (small stones) are common. They are usually made up of a mineral called calcium oxalate. They are easy to see on x-rays. They can contribute to a decline in the kidney function.
Chronic Kidney Diseases,

being very common in cats and characterized by an irreversible decrease in renal function that may stabilize or plateau for periods, but invariably, the condition progresses. Clinical studies showed that dietary modifications can slow the progression of the disease, prolong the survival and improve the quality of life. Some of the cats with CKD appear healthy while others have changes consistent with chronic diseases: an unkempt appearance, poor hair coat, weight loss, and/or muscle wasting.
Signs of chronic diseases are negative. Additional signs of uremia might be present, such as gastrointestinal ulcers or uremic halitosis. The International Renal Interest Society (IRIS) developed a system for staging severity of dysfunction of CKD in cats as in dogs
Stage I includes non-azotemic cats with CKD;
Stage II includes cats that are mildly azotemic, other plan polyuria/polydipsia, pets in one of these stages usually do not have clinical signs of kidney dysfunction. Occasionally cats in stage II have weight loss or selective appetite. However, many pets have clinical signs resulting from their kidney lesions (acute pyelonephritis, nephrolithiasis). Those with marked proteinuria or systemic hypertension due to CKD may have clinical signs related to those issues. Renal function is often stable or slowly progressive for an extended period in non-proteinuric, non-hypertensive cats with CKD stage I and II. However, when progression does occur, it is important to determine whatever the primary etiopathologic process underlying their CKD may be contribute to progression. Patients with stage I and II CKD should be evaluated with the goal of identifying and providing specific treatment for their primary renal diseases where possible, in addition, renal function should be monitored for possible progression of their CKD
Pets with moderate azotemia are classified as stage III CKD and they may have clinical signs referable to their loss of kidney function, however, with appropriate treatment, they typically do not have clinical signs of overt uremia. Since stage III CKD is typically progressive, in addition to identifying and treating primary CKD, a therapy designed to modify factors promoting progression of CKD may be of benefit.
Stage IV CKD includes patients with severe azotemia and usually clinical signs of uremia. Diagnostic and therapeutic initiatives in this stage include those appropriate for stage III patients as well as therapy designed to prevent or ameliorate signs of uremia.
Identifying clinical biochemical or hematological complications of CKD
When obtaining the history one should seek clinical signs that may date the onset of kidney diseases ( e.g Polyuria/polydipsia, weight loss, decrease appetite), information on possible congenital hereditary diseases, evidence of current or past infections, neoplasia, metabolic diseases, lower urinary tract signs or problems, drugs history ( current or past ) toxins exposure diet, appetite and/or evidence of previous kidney problems). Physical examination should emphasize dental and oral conditions, retinal examination for hypertensive lesions, hydration, edema, body condition score, hair coat quality, pulse rate, and quality, palpation of the urinary tract, bone pain, body temperature, and rectal examination, as well in cats the cervical area should be carefully examined for evidence of thyroid enlargement.
Test recommended:
Since most body systems are affected by CKD and uremia, the initial diagnostic database is board: arterial blood pressure, complete blood count ( CBC), complete serum chemistry panel including electrolytes, acid-base status, complete urine analysis, urine culture, survey abdominal x-rays and/or abdominal US. As well in cats, T4 testing should be performed to rule out concurrent hyperthyroidism.
Some pets with CKD have anorexia and nausea due to retention of uremic toxins, dehydration and biochemical alteration (azotemia, metabolic acidosis, electrolytes imbalances, mineral imbalances), anemia, or uremic gastroenteritis.

The diet

Energy: decreased energy intake due to inappetence or advanced renal failure may lead to poor body condition. Sufficient energy must be provided to maintain a good level of energy.
Fatty acids the average fat content in cats is about 12%, containing polysaturated fatty acids.
Antioxidants – CKD is a pro-oxidant state, beginning early in the condition and progressing as the disease worsens. Modification of oxidative stress may have benefit in managing CKD.
Water-soluble vitamins: Theoretically water-soluble vitamins are lost in increased rate in pets with CKD due to their polyuria.
Electrolytes hypokalemia (low sodium) and whole-body potassium depletion occur in 20-30% of the cats with CKD.
Acid-base balance – metabolic acidosis is common in cats with CKD due to retention of metabolic acids, lactic acid production, electrolyte imbalances, and/or consumption of dietary acids.
Moisture due to polyuria nature of CKD, dehydration may occur especially in cats.
Protein – azotemia is by definition an increase in the nitrogenous compounds in the blood most of which are derivate from dietary protein or catabolism of endogenous protein. Formulating a diet that contains reduced quantity, but highly biologically available protein is highly recommended in those cases. This may aid in amelioration of clinical signs associated with azotemia.
Several studies have demonstrated, in part due to dietary management, longer survival times and better quality of life in cats that have naturally occurring CKD. Most studies showed at least a two-fold increase in survival in cats fed a “renal failure diet”. Diets were most effective with stage II CKD.
Chronic kidney diseases are progressive, therefore, monitoring is important. Monitoring of nutritional management of CKD involves body condition score, body weight, and appetite, quality of life and biochemical parameters. The frequency of monitoring should be individualized to the patient and to the stage of the disease. Most animals should be monitored every 4-6 months in stage I or II CKD and more frequently in stage II and IV.

This blog is written by ABVC Vet dr. Alexandra Gulinescu