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WVC 2017: The Kidney Is Key - Update on CKD
At WVC 2017, Dr. Dennis Chew presented diagnostic and preventive information about chronic and progressive kidney disease in dogs and cats.
During a urology symposium at the Western Veterinary Conference in Las Vegas, Nevada, Dr. Dennis Chew, DVM, DACVIM, discussed the diagnosis of chronic kidney disease (CKD) and the prevention of progressive CKD.
Chronic renal insufficiency and renal failure are two branches of CKD, an insidious and progressive disease. CKD may be subclinical (an “accidental” discovery), or patients may show signs such as lethargy, weight loss, halitosis, hyporexia, vomiting, polyuria, polydipsia, and hypertension.
One cause of CKD is a renal maladaptation to increased pressure in the glomerulus, forcing proteins through the delicate tissue. Increased pressure may be secondary to diabetes mellitus or systemic hypertension. This damage causes a mesangial reaction that will result in glomerulosclerosis, causing a decreased glomerular filtration rate. This microtrauma becomes progressive and the kidney becomes dysfunctional.
The minimum database for CKD includes a thorough history, physical exam, urinalysis (including urine specific gravity, urine chemistry, urine protein:creatinine ratio), and serum chemistry panel (including blood urea nitrogen, creatinine, and phosphorus). Renal imaging via ultrasound and radiographs is also useful; evaluate the size and symmetry of the kidneys on radiographs. All cats with CKD should undergo renal imaging to rule out postrenal obstruction, as nearly 50% of cats in the United States with CKD have upper urinary tract stones.
The most important assessment for CKD is the urinalysis. According to Dr. Chew, “nothing shall come between thee and thy urine sample.” First morning urine samples have a higher concentration and are preferred.
Creatinine will increase at a defined rate as excretory, conservatory, and metabolic function of the kidneys declines. Creatinine is not a perfect test; a significant amount of damage needs to occur before creatinine will become elevated. Additionally, the creatinine level is impacted by muscle mass in a linear fashion (decreased muscle mass means decreased creatinine).
Creatinine levels are part of International Renal Interest Society (IRIS) classification. For canine CKD, the IRIS stages are as follows:
- Stage I: Nonazotemic
- Stage II: Mild azotemia (1.4—2.0 mg/dL)
- Stage III: Moderate azotemia (2.1—5.0 mg/dL)
- Stage IV: Severe azotemia (>5.0 mg/dL)
An “at risk” category has also been proposed for animals that have had a previous kidney insult or have a significant predisposition. Risk factors for CKD include chronic inflammation (eg, periodontal disease) and genetics (eg, Doberman familial nephropathy).
IRIS substages are assigned by evaluating proteinuria. Evaluating serial urine protein:creatinine ratio samples is the best way to test the degree of proteinuria; however, a technique called “pooling” may be more cost-effective. With pooling, equal volumes of serial urine samples are combined into a single sample and tested.
Symmetric dimethylarginine (SDMA) is another testing option. SDMA is excreted almost exclusively in the urine and is not dependent on muscle mass; it is released into the bloodstream when intranuclear protein is degraded. SDMA will increase before creatinine, allowing it to be a viable early assessment.
To prevent or slow the progression of CKD, phosphorus should be limited. Previous support for low-protein diets has been refuted; low-protein diets may be harmful, resulting in cachexia. Instead, phosphorus restriction may be the “single most powerful treatment,” according to Dr. Chew. Phosphorus mineralizes the kidney, worsening ongoing damage. Intestinal phosphate binders may be given with food to help bind excess phosphate. Use caution with aluminum salts due to the risk for aluminum toxicity. Dr. Chew’s preferred binder is lanthanum carbonate, but it is expensive; an alternative may be to use a combination of binders—half aluminum salt and half calcium acetate.
Dr. Chew also recommends treating CKD with calcitriol to decrease parathyroid hormone. Parathyroid hormone toxicity impacts many organs, especially bone and kidney. Calcitriol should be added when the serum phosphorus level exceeds 6.0 mg/dL. Significant improvement in lifespan has been reported in canine CKD with the use of calcitriol; the emerging recommended dose is 9 to 12 ng/kg every 3.5 days to help mitigate concerns for hypercalcemia.
Amanda Landis-Hanna, DVM, graduated from Auburn University in 2002. Since then, she has practiced small animal, exotic, shelter, and relief medicine. She was a VCA medical director for 7 years in California and Virginia, and she served as director of veterinary medicine for Voyce from 2013 to 2016. Dr. Landis-Hanna resides in Virginia with her family and rescue Labrador, Sophie.