Kidney 3: Diagnostic Tests

What is the indication for urinalysis?

To assess renal function and disease

What can a urinalysis tell you?

Renal concentrating ability

Integrity and function of nephron

Identify infections

What is the volume of urine you want for urinalysis?

As much as possible

How can you collect urine?

Off the floor

Free catch

Catheterization

Cystocentesis

How long do you have to do a urinalysis?

within 30 minutes or 12 hours if refrigerated

What is an adequately concentrated urine in dogs?

USG > 1.030

What is an adequately concentrated urine in cats?

> 1.035 - 1.040

What is the most likely cause of azotemia?

Pre-renal

What is isothenuria numerically?

1.008 - 1.012

What is happening during isosthenuria?

Kidneys are not diluting urine, usually a renal azotemia due to dehydration

What is hyposthenuria numerically?

USG < 1.008

What is happening during hyposthenuria?

Able to dilute urine but unable to concentrate

PCT and LoH is functional

Interreference with the function of the DCT and CD

What are the 3 general types of proteinuria?

Pre-renal

Renal

Post-renal

How do you definitively diagnose a renal proteinuria?

Biopsy technically but usually done by ruling out pre-renal and post-renal causes

Describe pre-renal proteinuria?

Glomerulus is normal and there is excess low molecular weight proteins that can pass through and overwhelms the PCTs reabsorption capacity

What proteins can normally pass through the glomerulus and should be reabsorbed by the PCT?

Bence-Jones proteins

Hemoglobin

Myoglobin

What are Bence-Jones proteins?

Light chains of immunoglobulins

What are the functional causes of renal proteinuria?

Fever, strenuous exercise, stress, overheating heat stroke

UPC is usually 1-2

What is a functional renal proteinuria?

Transient event not due to a lesion that should resolve on multiple UPCs

What are the causes of a pathological renal proteinuria?

Glomerular

Tubular

Interstitial

Describe a glomerular proteinuria

Due to a disruption in the filtration barrier with a UPC > 2

What are the causes of glomerular proteinuria?

Glomerulonephritis

Amyloidosis

Injury to the glomerular capillary wall

Congenital abnormalities in the glomerular basement membrane

What is a tubular proteinuria?

Impaired ability of the PCT to reabsorb protein UPC is usually < 2

What are causes of tubular proteinuria?

Fanconi syndrome

Ischemia

Nephrotoxins

Infections

What can cause a interstitial proteinuria?

Disease in kidney interstitium such as infiltrative or inflammatory disease or renal hemorrhage

What is post-renal proteinuria?

Protein originating from any part distal to the kidney

What can cause post-renal proteinuria?

Hemorrhage

Infections

Inflammation

Neoplasia

Urolithiasis

Reproductive pathology

What is the renal threshold for glucose in dogs?

180-200 mg/dL

What is the renal threshold for glucose in cats?

200-290 mg/dL

What can cause glucosuria?

PCT dysfunction

Describe the significance of bilirubinuria

Dogs have a lower threshold but it is always significant in cats

What are pathological causes of bilirubinuria?

Cholestasis will have increased ALP too

Hemolytic anemia

What are the markers of GFR?

BUN

Creatinine

SDMA

Describe BUN

Freely filtered by glomerulus and 60% is reabsorbed in the PCT

What does ADH do to BUN levels?

Increases urea reabsorption in the DCT and will increase BUN in the blood

What are some non-renal causes of increased BUN?

Increased protein metabolism and uptake from GIT

Increased catabolic processes

What can increase protein metabolism and uptake and thus BUN?

High protein diet

GI bleeding

What can increase catabolic processes and thus BUN?

Infection, fever, prolonged exercise, rhabdomyolysis/necrosis, glucocorticoids, starvation

What are causes of decreased BUN?

Decreased production

Polyuria

What can cause decreased production of BUN?

Hepatic insufficiency

Abnormalities in the urea cycle

What is creatinine?

Breakdown of creatine and creatine phosphate from muscle metabolism

What is production of creatinine dependent on?

Muscle mass

Why is creatinine a more accurate assessment of GFR than urea?

Freely filtered by the glomerulus and has no tubular reabsorption

What are non-renal causes for increased creatinine?

Increased muscle mass

What are non-renal causes of decreased creatinine?

Cachexia and sarcopenia

What is more sensitive for detecting early renal disaese?

SDMA

Describe SDMA

Synthesized by all nucleated cell and is independent of muscle mass

What are the 5 basic functions of the kidney?

Formation of urine

Regulation of acid-base

Water conservation

Maintain electrolyte balance

Endocrine functions

What are causes of pre-renal azotemia?

Decreased perfusion of the kidney

How do you resolve a pre-renal azotemia?

Rehydration

Restore BP and CO

What are post-renal azotemia causes?

Ureteral or urethral obstruction

Rupture somewhere along urinary tract

What is seen on history of a post-renal azotemia?

Changes in urination patterns

Straining to urinate

Inappropriate urination

What is on physical exam of a post-renal azotemia?

Painful abdomen

Abdominal distension

Large, firm bladder

How can you confirm a post-renal azotemia?

Diagnostic imaging: US, radiograph, contrast

Peritoneal fluid analysis

What is the peritoneal fluid analysis of a post-renal azotemia?

Fluid : blood K+ ratio of > 1.4:1 in dogs or 1.9:1 in cats

Fluid : blood creatinine ratio of > 2 :1

What causes renal azotemia?

Decreased numbers of functional nephrons

T/F renal azotemia patients are isosthenuric?

True

What is a renal azotemia?

Inadequately concentrated urine in the face of dehydration of azotemia

Describe bicarbonate reabsorption in the kidney

Freely filtered by the glomerulus

Nearly completely reabsorbed by the PCT

Describe the kidney’s role with acid secretion

Excretion of H+ with ammonia

What is the path of ammonia in the kidney?

Generated intracellularly in the PCT, protonated and excreted in the form of NH4+

What is the most important way kidneys excrete acid?

Protonated ammonia as NH4+

What is metabolic acidosis?

Ability to increase renal ammonia production to maintain H+ excretion is lost

What can chronic acidosis cause?

Muscle wasting, anemia, hypoalbuminemia, uremia, renal osteodystrophy, RAAS activation, inflammation

What can cause decreased urine concentrating ability?

Increase solute load that needs to be filtered

Disruption of the architecture and countercurrent mechanism of the medulla

Altered responsiveness to ADH

What is the most common electrolyte change with kidney disease?

Hypokalemia

What can cause hypokalemia?

Urinary potassium loss

Decreased dietary intake

Metabolic acidosis

Activation of RAAS

What can cause hyperkalemia?

Medication (ACE inhibitors or blockers)

Anuria or oliguria

Post-renal

What can cause hyperphosphatemia?

Decreased renal excretion leading to PTH secretion and secondary renal hyperparathyroidism

What are the endocrine functions of the kidney?

RAAS system to regulate hypertension

T/F hypertension is a progression of renal disease?

True

What % of cats with CKD get hypertensivee?

20-65%

What are the target organs of hypertension?

Heart, brain retinas,

Other than renal failure what else can cause anemia?

Reduced RBC lifespan

Iron sequestration or deficiency

Gastric ulcers

Poor nutrition

Iatrogenic