Diagnosis of kidney disease
Linda E. Luther, DVM, DACVIM (SAIM)
Small Animal Track
November 2012
Learning objectives
 Review renal physiology.
 Describe how blood and urine tests, as well as radiographs and ultrasound, can help to
define kidney disease.
 Describe normal and abnormal systemic blood pressure in dogs and cats.
 Discuss how to interpret Leptospirosis titers.
 Describe the indications and contraindications for a kidney biopsy.
Physiology
 Functional unit is the nephron.
 Glomerulus: Filtration (GFR)
 Tubules: Reabsorption and secretion
 1 million nephrons/kidney!
Functions of the kidneys
 Excrete waste products
 Conserve water
 Electrolyte and acid/base regulation
 Produce hormones
o Erythropoietin (red blood cell production)
o Renin (regulation of blood pressure)
o Calcitriol (calcium and phosphorus regulation)
Some diseases of the kidneys

Acute renal failure

Chronic kidney disease (CKD)

Pyelonephritis

The nephron
Diagnosis of kidney disease combines the
interpretation of:

Clinical signs

Blood tests
Glomerulonephritis

Urine tests

Leptospirosis

Blood pressure determination

Perirenal pseudocyst

Function tests

Polycystic kidney disease (PKD)

Radiographs

Calculi

Ultrasound

Neoplasia

Biopsy

Renal dysplasia
Clinical signs of kidney disease
 PUPD
 Anorexia
 Vomiting
 Weight loss
 Abdominal pain
 Or…nothing
Blood tests
 CBC
o Hematocrit, leukogram, platelet count
 Blood chemistry profile
o BUN, creatinine, calcium, phosphorus, sodium, potassium, albumin, HCO3
 Azotemia
 Increased BUN and/or creatinine
 Azotemia ≠ kidney disease and kidney disease ≠ azotemia

Underlying mechanisms
o Pre renal: Dehydration
o Renal: Renal failure
o Post renal: Urethral obstruction, uroabdomen
 Need Uspgr to differentiate prerenal vs.
renal azotemia!
 Loss of 66% of nephrons: Isosthenuria
 Loss of 75% of nephrons: Azotemia


Leptospirosis testing in dogs
o Titers
 Vaccination vs. disease
 Acute vs. convalescent
 4-fold increase or decrease in 1-3 weeks
 Vaccination titers often less than 1:800, but up to 1:3200 possible
 PCR to detect organism
 Blood in very early infection
 Urine 10-14 days post infection
 False positives and false negatives can occur
 Not affected by vaccination
Lyme testing in dogs
o Labs and Goldens w/increased risk of Lyme nephritis
 Other breeds less likely but still may be at risk
o Screen for proteinuria if positive for Lyme
o Screen for Lyme if proteinuric
Urine tests
Specific gravity
o
o
o
Urine dipstick
Normal ‘depends’
1.003 - >1.080
Isosthenuria


1.008-1.012 if normal hydration
1.012-1.018 if dehydrated

>1.030 dog; >1.035-1.040 cat:
Can concentrate urine
Urine protein
o
o
o
o
Protein
Blood
Glucose
pH
Urine sediment
o
o
Present? Significant?
Methods
 Dipstick/SSA
 UPC
 Microalbumin

Urine protein
o Urein protein/creatinine ratio (UPC)
 Renal vs. post-renal

rbcs
wbcs
Epithelial cells
Casts
Crystals
Bacteria
✓ sediment first. If active sediment: Post renal proteinuria
Repeat 3x q 2 wks if not azotemic. If azotemic (and urine not
concentrated), assess proteinuria as significant.
 Normal
 < 0.4 in cats
 < 0.5 in dogs
 Tubular disease
 0.5-1
 Glomerular disease
 ≥ 2.0
Microalbuminuria (albumin ≤ 30 mg/dL)
 Warning sign of glomerular disease in humans
 In vet med very sensitive, but not specific
 Infectious, immune, neoplastic disease increase it well as renal
disease
 Positive predictive value, negative predictive value uncertain

o
o
o
o
o
o
o

Urine culture with MIC sensitivities
Blood pressure
 > 160 mmHg
 65-75% CKD dogs and cats have increased BP
 Fundic exam may detect retinal changes
 Check blood pressure when hydration is normal
Function tests: GFR
 Serum creatinine level is used as an approximation/to stage CKD
o Low sensitivity, may vary with hydration status, muscle mass, if fasted or not
o Serial creatinine levels in an individual animal may indicate early kidney disease.
o Other biomarkers of early kidney disease are being investigated, so stay tuned.
 Clearance studies are more sensitive and specific, but less available/practical
o Inulin, creatinine, iohexol
o Scintigraphy
Kidney imaging
 Radiographs: Size, mineralization
o Large kidneys
 Acute disease
 FIP, Lepto, LSA, EG toxicity, PKD
o Small kidneys
 Chronic disease

Ultrasound
o There are a limited number of ways the kidneys can respond to a variety of
disease processes. Several ultrasound changes observed will be nonspecific.
o Ultrasound findings further characterize disease.
o Ultrasound does not predict renal function.
o Ultrasound changes that may be observed include:
 (Increased/decreased size) (use radiographs to best judge kidney size)
 Overall echogenicity changes
 Cortical cysts/polycystic kidney disease
 Decreased corticomedullary distinction
 Hyperechoic corticomedullary rim
 Calculi
 Renal pelvic dilation
 Masses
 Infarcts
 Subcapsular changes
 Pseudocysts
 Fluid/thickening
 Hematomas/Abscesses
Kidney biopsy
 The value of kidney biopsy will likely increase in the near future as current
knowledge/discussion increases.
 Indicated when it will make a difference in making a specific diagnosis, deterimining
prognosis and/or establishing or altering therapy.
o Renal dysplasia in a breeding line
o Masses
o Acute renal failure, specifically acute nephritis not due to Leptospirosis or
pyelonephritis
o Lyme nephritis suspected
o Subcapsular fluid or thickening (FNA)
o Protein losing nephropathy*

Contraindications
o Small patients (< 5 kg), uncontrolled hypertension, coagulopathy, pyelonephritis,
cysts, hydronephrosis, severe azotemia

Complications
o Hemorrhage

Processing
o Light microscopy (LM)
 In formalin
o Electron microscopy (EM) for glomerular diseases to verify presence of
immune complexes and their specific location in the glomerulus
 In 3% glutaraldehyde in phosphate buffer
o Immunofluorescence (IF) to identify type of immune complexes (IgG, IgA,
IgM, complement)
 Frozen or in Michel’s solution
Methods
o Always with general anesthesia
Core biopsy processing
o Biopsy cortex only
(Lees & Bahr, 2011, p. 214))
 Where the diagnosis is (glomeruli)
 Safer as this avoids the arcuate arteries
o Wedge
 Largest # glomeruli
 Best for renal dysplasia
 Surgical
o Core or Tru-Cut
o 14-18G
o Blind, U/S-guided, surgical or laparoscopic?
o Laparoscopic best quality, lowest risk
o Surgical second best

Diagnosis of kidney disease references
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Lees GE, Berridge BR. Renal biopsy—When & Why. NAVC Clin Brief 2009:26-29.
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