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What are the 3 steps in renal insufficiency at what percentage loss of function occur and what occurs at each stage

1) Regulatory failure
- Loss of ≥66% of nephron function
- Failure to concentrate urine→ polyuria
- Metabolic acidosis and electrolyte abnormalities
2) Excretory failure
- Loss of ≥75% of nephron function
- Nitrogen wastes accumulate
3) Biosynthetic failure : Erythropoietin
Non-regenerative Anaemia


List 3 causes of primary renal damage and 4 causes of secondary renal damage (decreased tubular function)

1) Toxic insult – ethylene glycol, grapes, lillies
2) Parenchymal damage and fibrosis - inflammation and infectious process
3) Nephritis - inflammation of the kidneys
1) Primary diabetes insipidus - failure to excrete ADH
2) Secondary diabetes insipidus
3) Hypercalcemia, Hyperadrenocorticism, Pyometra
4) Loss of medullary concentration gradient – depletion of NaCl and urea


List the 4 ways renal function is assessed and what is tested within each test

1) Excretion of waste products
- Urea and Creatinine in mammals
- Uric acid in birds and reptiles
2) Fluid and electrolyte balance - dehydration
- Urine concentration
- Serum and urine electrolytes
3) Acid-base regulation - Acidosis, alkalosis
- Serum bicarbonate
- Urine pH
- Blood pH and blood gases
4) Production of erythropoietin
- RBC count/PCV/Haemoglobin or measure EPO


How do you measure GFR in urinalysis

Measurement of Glomerular Filtration Rate (GFR) - don't measure directly but indirectly through the 4 methods of assessing renal function


List 6 uraemias

1) Mucosal ulceration
2) Halitosis - bad breath
3) Vomiting
4) Depression
5) Weakness
6) Anorexia


Describe the 3 broad causes of azotaemia and examples within

Decrease Renal blood flow - something upstream
- Dehydration - reduced blood volume
- Severe haemorrhage
- decrease in functional nephrons, decrease GFR
Decrease urine output- get leakage of urine into abdomen and contents reabsorbed into circulation
- Tumour, inflammation - nephrosis
- Urinary tract disease
- Obstruction - kidney stones


urea filtration, reabsorption where occur and what are the 2 sources of urea

- Sources
1) Liver protein catabolism → ammonia → urea
2) Large intestine (small amount)
- Freely filtered by glomerulus
- Some tubular reabsorption - especially with slower urine flow


What are the two main reasons serum urea increases and give examples within

1) ↓ glomerular filtration rate
- Decreased renal perfusion = prerenal
- Loss of nephron function = renal
- Obstruction of urine flow = postrenal
2) ↑ increased protein breakdown - prerenal
- High protein diet
- GI bleeding into the gut - increase protein breakdown in the gut, increase microbe convert to ammonia and liver convert to urea and excret into circulation on its way to the kidney
- Protein losing enterophathy


Which is more specific for pre-renal azotaemia urea or creatinine

Urea increases more with pre-renal azotaemia than creatinine increases - less specific


What are the 3 main downfalls of using urea as a measurement of azotaemia and why

1) Less useful in assessing renal function in ruminants and horses - use creatinine mainly
- Ruminants excrete urea via rumen
- horses excrete urea via large intestine
- Excretion depends on nitrogen intake
2) Not useful in birds and reptiles
- Protein catabolism →ammonia → uric acid
3) Increases can reflect dehydration


creatine filtration, excretion and reabsorption and why more specific then urea but what animal not used in

- Freely filtered by the glomerulus
- Small amount excreted in GIT
- No tubular reabsorption - more specific → better indicator of decreased GFR than urea
- Concentration not affected by diet
not used in birds as only see once advanced renal disease


List the 3 main reasons see increase serum creatinine and 1 decrease and examples within

1) ↑ muscle mass → ↑ creatinine
- Greyhounds are higher than labrador
2) ↑ muscle breakdown → ↑ creatinine
- Training or rhabdomyolysis
- When stable with weight and muscle turnover most effective
3) ↓GFR
- Decreased renal perfusion = prerenal
- Loss of nephron function = renal
- Obstruction of urine flow = postrenal
4) Decreases with generalized muscle wasting
- Could mask kidney disease as if occurring at same time one make go up either decrease so overall no change


What is the downside with creatinine

- Little change in creatinine until advanced renal failure
- normal creatinine doesn't mean don't have renal dysfunction
- need to explore early onset markers


uric acid in birds and reptile list 4 things that increase uric acid and why difficult to use

1) Renal disease (low sensitivity) - only really see increase in advanced renal disease
2) Profound dehydration - prerenal
3) Ovulation - very hard to know
4) Diet (high protein)
- Higher levels are seen in carnivorous species
- Hard to get good reference intervals


SDMA what does it stand for, when released, when increased levels seen and what causes increase levels

- Symmetrical dimethylarginine
- Released with proteolysis and excreted through the kidneys
- Increased levels are seen with ≥ 40% loss of renal function
- Slightly higher levels are seen in Greyhounds
- Increases with any cause of decreased GFR
e.g. dehydration, hypovolaemia (pre-renal)


List 3 clinical signs of renal azotaemia and pre-renal azotaemia

renal azotaemia
1) Polyuria and polydipsia
2) Anuria or oliguria
3) Inadequately concentrated urine
Pre-renal azotaemia
1) Concentrated urine - actively resorbing water
2) Evidence of dehydration
○ Vomiting, decrease skin turgor, dry tacky membranes, increase in urea and creatinine
3) Evidence of increase protein breakdown in GIT
○ Melena - blood in faeces
○ Increase in urea only, creatinine will be normal


Urine Specific gravity what measure with, what is it, what does it indicate and what does it reflect

- Refractometry
○ If above 1.000 greater than water (always the case with urine)
○ USG is ratio of refractive index of urine compared to water
○ Indication of tubular function = ability of tubules to absorb or excrete water
○ Reflects urine osmolality
- High USG = more concentrated urine
- Low USG = less concentrated urine


What are the 3 ways to measure fluid and electrolyte balance

1) Urine specific gravity
2) Dipstick reagent pad
3) urine osmolality


1) If have azotaemia + concentrated urine =
2) Azotaemia + inadequate urine concentration =

1) = dehydration - prerenal
2) = renal


List 5 factors that influence urine concentration

1) Number of functional nephrons
2) Renal medullary hypertonicity
○ Resorption of NaCl & Urea
○ Renal medullary blood flow
3) ADH secretion and action - RAAS mechanism
- Extra-renal factors
○ Hydration status
○ Serum electrolytes
○ Concurrent diseases - inhibiting ADH function - diabetes insipidus
○ Drug therapy e.g. diuretics
4) renal insufficiency as unable to conserve water and electrolytes and unable to excrete N wastes


what are the 3 things that urine concentration does not distinguish

1) reversible from irreversible
2) acute from chronic renal disease
3) primary from secondary renal insufficiency


Progression of renal insufficiency what do you see:
1) ≥ 40% loss of function →
2) ≥ 66% loss of function →
3) ≥ 75% loss of function →

1) ↑ SDMA
2) polyuria
3) azotaemia


postrenal azotaemia findings of examination, history and histology

- History – stranguria or dysuria
- Examination/imaging findings:
○ Decreased urine output - leaking into abdomen or banking into the bladder
○ Distended bladder - pressure can build back to the kidney causing kidney disease
○ Uroabdomen
Hyperkalaemia - increase in potassium


What are the 2 main causes of postrenal azotaemia and examples within

1) Obstruction of urine flow
○ Urinary calculi - urinary stones could be suck in urethra
○ Urethral plug
2) Internal urine leakage/uroabdomen
○ Ruptured bladder - can be seen with contrast leaking into abdomen in radiograph
○ Torn ureter / urethra
○ Patent urachus


List the other 8 changes with renal insufficiency

- Potassium
- Phosphate
- Sodium
- Chloride
- Bicarbonate
- Albumin
- Anaemia
- Amylase and Lipase


potassium what causes increase and decrease

- Hyperkalaemia - Anuric (acute kidney injury), oliguric or obstructive disease (post-renal)
○ Decreased GFR
○ Decreased secretion
○ Associated acidemia
- Hypokalaemia - Polyuric renal disease
○ Increased urine flow rate
○ Reduced tubular function - chronic kidney disease
→ decreased potassium absorption


phosphate what causes with increase and decrease

- Hyperphosphataemia
○ Decreased GFR - renal (generally more severe)
○ Bone activity (young animals) - also get high ALT
○ Sample haemolysis - pre-renal
- Hypophosphataemia common in horses with chronic kidney disease uncommon in other species


calcium what occurs with chronic kidney and acute kidney disease

Chronic Kidney Disease
→ Hypocalcaemia in dogs and cats, rarely hypercalcaemia
- secondary to hyperphosphatemia and decreased Vitamin D production
→ Hypercalcaemia in horses and rabbits
- High calcium diet
- Renal excretion controls excess and when get disease hard to keep up with the calcium absorbed from the gut
Acute Kidney Injury
→ Hypercalcaemia or Hypocalcaemia


magnesium what occurs with decreases GFR

Decreased GFR - Hypermagnesaemia
- Don't have on a routine biochemistry


sodium and cholide when elevated

- Elevated with dehydration
- Variable level with renal insufficiency
○ Depends on water loss vs electrolyte loss
○ Changes masked by dehydration
○ Selective Cl loss with vomiting