Chronic kidney disease (CKD) is now the most common problem seen in older feline patients. It is less common in dogs, but we are nevertheless seeing it more often as our patients live longer. The causes are unknown, but some possible contributors include excessive vaccination, chronic infections and/or highly concentrated urine.
The early signs of CKD are subtle and rarely noticed by owners. They include slow weight loss with a mild increase in drinking and urine volumes as the serum creatinine climbs above 140 mMol/L = 1.5 mg/dL. Veterinary diagnosis is made when accurate body weight decreases and blood tests are done.
Assessing this disease includes:
• Kidney excretion capacity by measuring Glomerular Filtration Rate (GFR) — serum creatinine
• Secondary Renal Hyperparathyroidism — serum calcium (Ca) and phosphorus (P)
• Kidney potassium (K) tubular loss — Serum K
• Erythropoietin production — Packed Cell Volume (PCV) or hematocrit
• Renal protein loss — urine protein:creatinine ratio (UPC)
• Hypertension — blood pressure (BP)
• Thyroid function status in cats – T4
The tests required for adequate assessment of renal function:
1. Thorough history (owner observations) and physical examination 2. Body weight and Body Condition Score — cats and dogs under 10 kg = 22 lb need to be weighed on a paediatric/baby/cat scale, not on adult bathroom scales or walk-on dog scales. Reliable human baby scales are available online for less than $70. All patients should be weighed at every vet visit, and the weight recorded in their files. 3. Complete blood count, CBC 4. Serum chemistry, with T4 in the cat 5. Urinalysis including culture and sensitivity (C&S) and UPC 6. Blood pressure
Normal urine results: Urine specific gravity > 1.030 in dogs (first morning sample) Urine specific gravity > 1.030 in cats, if their eating canned food without water added Urine protein negative UPC < 0.2 Urine C&S negative
Normal BP arterial/systolic < 160 mm Hg. This includes the “white coat” effect but BP should be done first with the owner present and the patient not “freaking out”.
What happened to urea?
Serum urea or nitrogen levels are influenced by many factors, making urea an unreliable indicator of kidney function. Some of these factors include:
• Amount of protein eaten (important)
• Time since eating
• Degree of protein digested to amino acids
• Proportion of protein absorbed
• Level of intestinal bacteria
• Liver function (the most important factor)
• Protein loss through the skin, intestines and/or urinary tract
• Catabolic processes occurring within the body, such as infection or cancer
Urea is non-toxic, water soluble and has a neutral pH. It is a poor indicator of GFR. At best it is a minor indicator of seriously decreased liver function.
Thanks to the International Renal Interest Society (IRIS, iris-kidney.com), we now have better diagnostic and staging information. IRIS is composed of leading international veterinary nephrologists, and has made evaluating, interpreting and monitoring CKD much clearer with their evidence-based stages and recommendations.
Stage and clinical signs Test results Stage 1 — Asymptomatic Creatinine < 140 = 1.5 depending on dog muscle mass; other evidence of kidney disease, e.g. ultrasound Stage 2 — Mild PU/PD Decreased appetite Creatinine in dogs 125 – 180 = 1.4 – 2.0 depending on size, diet and muscle mass Creatinine in cats 140 – 250 = 1.5 – 2.8 Potassium 3.5 – 5.0 Phosphorus < 2.0 = 6.0 Stage 3 — PU/PD Dehydration Decreased appetite Weight loss Constipation Creatinine in dogs 180 – 440 = 2.0 – 5.0 depending on size, diet and muscle mass Creatinine in cats 250 – 440 = 2.8 – 5.0 PCV < 20% Stage 4 Depressed Inappetent Vomiting and/or diarrhea Creatinine > 440 = 5.0
The initial diagnosis of CKD is usually made when the dog or cat is losing weight for no apparent reason, and is based on a thorough history and physical examination. With a diagnosis of “weight loss of unknown cause”, pet owners and I elect to investigate further with CBC, chemistry (plus T4 in cats) and urinalysis.
Once the diagnosis is made (Dx CKD Stage 2 with no complications — no urinary tract infection, no proteinuria, no other disorders) we discuss nutrition and the importance of maintaining body weight by getting the animal to eat enough food that he likes. My recommendations for ongoing monitoring, as long as the patient is doing well, is to recheck and run selective blood tests every six months. My experience has pushed me to keep CKD patients eating and drinking with potassium levels above 4.5 mMol/L or mg/dL and phosphorus levels below – 2.0 mMol/L = 6.0 mg/dL. This seems to ensure appetite and activity. Our management and therapeutic aims are to maintain quality of life as well as activity and body weight. Below are the blood levels we aim to maintain:
Blood Test Dogs Cats Hematocrit or PCV > 39% > 25% Creatinine Stable or only slowly increasing Stable or only slowly increasing Potassium 4.0 – 5.0 mMol/L or mg/dL 4.0 – 5.0 mMol/L or mg/dL Phosphorus 0.9 – 1.5 mMol/L 2.8 – 4.7 mg/dL 0.9 – 1.5 mMol/L 2.8 – 4.7 mg/dL
Cats with CKD should be examined by a veterinarian every six months. Ideally, at that time, the following tests should be done: CBC, serum chemistry, T4, UA and BP. Minimal testing involves PCV and kidney panel (and T4 for cats). The kidney panel is available at some commercial laboratories (I only use commercial laboratories for my patients’ blood tests as I want the most accurate results available and they are quality controlled).
The kidney panel is financially advantageous as it includes urea (useless), creatinine, electrolytes (K is so important in cats), calcium and phosphorus. For my feline patients, I add T4. We do a PCV in clinic. The total price of blood collection, courier, lab fee and my interpretation over the phone is one I find owners are comfortable paying every six months. This is in addition to my half-hour consultation fee. Conversely, the price for the ideal of CBC, serum chemistry, T4 in cats, UA and BP is two-and-a-half times the kidney panel and is cost restrictive for most of my clients every six months.
The progression of CKD is completely unpredictable. I used to think, based on my experience, that dogs with CKD died within three months and cats within three months to three years. No longer. Either we diagnose CKD much earlier or we enable them to live much longer. I think the latter is the case. Maintaining body weight is the key.
1. Zoe, a 16-year-old medium-sized border collie/Corgi cross was diagnosed with CKD Stage 2 six years ago. She has maintained her weight and active lifestyle on a home-prepared diet. She has not developed even mild anaemia although we are struggling to control her serum phosphorus. She is still going strong.
2. Most of my CKD cats live longer than five years but Tuesday was an exception. She was ten years old when she was first brought to me. She was already in CKD Stage 2 advanced. My therapeutic approach was to “feed her anything she will eat” use appetite stimulants, and control her low potassium, high phosphorus, constipation, hyperthyroidism and subcutaneous fluids. She lived happily for another 11 years and died at the ripe old age of 21.
3. Hendrix is a 13-year-old tabby cat in CKD Stage 2. He has always eaten enthusiastically and was maintaining his weight until one month ago. The owner had purchased a home baby scale and weighs Hendrix weekly. (As a practicing veterinarian in the real world of clients who love their pets but often have financial concerns, I encourage owners to monitor their cats’ progress by weighing them once a week on a baby scale. The cat’s weight and appetite, along with the owner’s assessment of how the pet is doing, are pretty reliable as to the status of the animal.) Four weeks ago, still eating very well, Hendrix’s weight started slowly decreasing. A phone call to us resulted in a simple recommendation: blood tests – CBC, serum chemistry, T4. We found the T4 had increased significantly from previous values; we can control hyperthyroidism.
The diagnosis and staging of chronic kidney disease (which is relevant to management) requires a thorough history and physical examination, evaluation of the weight loss and body condition score of the patient, CBC, serum chemistry, urinalysis, blood pressure, and T4 in cats. Ideally, ongoing monitoring would involve repeating these tests at six-monthly checkup examinations (body weight and condition score, history, physical examination, and discussion as to how the patient and owner are coping). However, depending upon veterinary judgement, a kidney panel and PCV (plus T4 in cats) may provide all the relevant information required for therapeutic advice.
Dr. Lea Stogdale, DVM, Diplomate ACVIM, graduated from the Faculty of Veterinary Science, University of Melbourne, Australia in 1970. She worked in general practice in Australia and England before teaching veterinary medicine in South Africa and Saskatoon for eight years. Dr. Stogdale passed the veterinary small animal internal medicine specialty board exams in 1981 to become a Diplomate in the American College of Veterinary Internal Medicine. She has worked in emergency and pet practice for 25 years, taking a special interest in diabetes of dogs and cats, complementary medicine and nutrition (aesopsvetcare.wordpress.com).
Normal creatinine levels in dogs
Serum creatinine mainly comes from the muscles (the steady breakdown of creatine phosphate) with a small amount being contributed by meat in food. Hence, it is preferable to collect a fasting sample especially if a dog is being fed a high protein diet. The muscle mass of the dog influences his serum creatinine level. In humans, women have 10% to 20% lower normal serum creatinine levels than do men, due to their lower muscle mass. Very small dogs with little muscle mass have lower normal serum creatinine levels while large athletic dogs, especially greyhounds, have higher normal serum creatinine levels.
Dog size SI units US units Miniature (0 – 10 kg) 40 – 90 mmol/L 0.45 – 1.0 mg/dL Medium to large (average) (11 – 45 kg) 50 – 125 mmol/L 0.55 – 1.4 mg/dL Giant and athletic dogs (>45 kg and greyhounds) 80 – 195 mmol/L 1.0 – 2.2 mg/dL Modified from Dr David Polzin, University of Minnesota