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Dog Kidney Health

12/29/2020

Patricia Thomblison, DVM, MS

The kidneys play a vital role in the body. In addition to removing waste from the blood they also help control blood pressure, make hormones and enzymes, and regulate essential minerals such as potassium and sodium. The nephrons are the functional unit of the kidney, consisting of glomerulus and its associated tubule. The glomerular filtrate passes through the tubule and emerges as urine.

 

Disease of the kidney

Chronic kidney disease (CKD) is the most common disease affecting the kidneys of dogs1, but other damage to the kidney can occur including those caused by injury, infection, toxins and cancer. Some kidney disease is familial, and some is caused by uroliths and/or obstruction. CKD is defined as kidney damage present for at least 3 months, with or without decrease in glomerular filtration rate, or greater than 50% reduction in GFR persisting for at least three months. The cellular structure of kidneys are not capable of regenerating like the liver can, so significant damage to the kidneys is essentially permanent.  Some acute insults to the kidneys can be halted and reversed to minimize potential for long lasting damage.

 

Nephroliths and uroliths

Stones of the urinary tract are not uncommon in dogs and these may occasionally be found in the kidney. The mineral composition of the stones dictates treatment options. General recommendation are to increase water consumption to keep the urine dilute. Manipulation of the urine pH may be helpful depending upon the type of minerals in the stone.

 

Diagnosing Chronic Kidney Disease

The terms chronic kidney failure or chronic renal failure does not mean that the kidneys have stopped working. There is no uniform agreement on the specific definitions so the International Renal Interest Society (IRIS) developed a scheme to classify the severity of CKD into four stages. The first staging is based on the concentration of fasting blood creatinine. Further evaluation includes blood pressure and the presence of proteinuria.

Step 1

Chronic kidney disease has an insidious onset and there may be no clinical signs at first. Pet owners may not notice the early signs of drinking more water and urinating more. Other signs may include weight loss, decreased appetite, lethargy, dehydration, and vomiting. At the early stages the physical examination findings may be normal. The first abnormal physical exam findings may include palpable kidney abnormalities, evidence of weight loss, and hypertension. Patients that have a history of exposure to nephrotoxins, older patients and some breeds should be evaluated as well. If they have elevated fasting blood creatinine or symmetric dimethylarginine (SDMA) levels or both, the dog should be staged with CKD.

Step 2

Staging is a process to determine what appropriate treatments are and to monitor the patients. Key clinical chemistries include baseline fasting blood creatinine and/or SDMA levels measured on at least two occasions in a hydrated stable patient. Substages are based on proteinuria and blood pressure. The patient should be re-evaluated over time and moved to different stages as needed.

Canine -IRIS Staging of CKD2

 

Stage 1

Stage 2

Stage 3

Stage 4

Blood urea nitrogen

No azotemia

Mild azotemia

Moderate azotemia

Severe azotemia

 

Creatinine (mg/dL)

< 1.4

1.4-2.8

2.9-5.0

> 5.0

Symmetric dimethylarginine (SDMA

սg/dL

< 18

18-35

36-54

>54

Urine Protein Creatinine Ration (UPC)

Nonproteinuric <0.2 0.5

Borderline proteinuric 0.2–

Proteinuric >0.5

 

Systolic Blood Pressure mmHG

Normotensive <140

Prehypertensive 140-159

Hypertensive 160-179

Severely Hypertensive ≥ 180

 

 

 

 

 

References:

  1. Chronic Kidney Disease, Part 1: Overview. Hutchinson D, Forrester SD, Rollins AW, et al. Clinician’s Brief.
  2. http://www.iris-kidney.com/guidelines/staging.html