Clinical Pathology: Tests for Renal Function and Integrity

Question 1

What are the functions of the kidneys?

Answer 1

• Excretion of waste
• Control of body fluid balance- electrolytes, acid-base, blood pressure
• Production of hormones- erythropoetin, calcitriol, renin

Question 2

What do nephrons excrete?

Answer 2

• Urea
• Creatinine
• K+
• H+
• PO4
• Ketones and lactate

Question 3

What are the recommended tests for renal function?

Answer 3

Blood tests
* Biochemistry- urea creastine, electrolyte balance
* Haematology
* Blood gas analysis

Urinalysis
* Always- USG, dipstick, sediment
* Maybe- UPC ratio
* Rarely- fractional excretions

Question 4

How can GFR be estimated?

Answer 4

Urea and creatinine

urea made in liver from ammonia

Creatinine- produced in a muscle, filtered by glomerulus

Iohexol- rarely done

Question 5

What can cause an increase and decrease in urea?

Answer 5

Increase:
* Decreased GFR
* Mild increase:
Upper GI haemorrhage
Recent meal
Catabolism- fever

Decrease:
* Severe liver disease or portosystemic shunt
* Low protein diet
* Aggressive fluid therapy
* PUPD
* Young animals

Question 6

What can cause an increase or decrease in creatinine?

Answer 6

Increase:
* Decreased GFR
* High muscle mass
* High protein diet

Decrease:
* Reduced muscle mass

Question 7

What can cause pre, renal, and post renal azotaemia?

Answer 7

Pre-renal
* hypovolaemia, shock, heart failure- dehydration/decreased CO

Renal- chronic or acute

Post-renal- urethral obstruction, urinary tract rupture

Question 8

What is the maximally concentrated urine specific gravity in dogs and cats?

Answer 8

1.030 in dogs
1.035

If urine above this- urine has been concentrated

Question 9

At what % of nephrons are lost for renal azotaemia?

Answer 9

75%

Question 10

What are other markers of GFR?

Answer 10

• SDMA- symmetrical dimethyl arginine
• Iohexol clearance

Question 11

What are the electrolyte changes in kidney disease?

Answer 11

• Hyperphosphataemia- horses go hypo
• Calcium
• Potassium

Question 12

How is calcium and potassium affected with kidney disease?

Answer 12

Calcium:
* Increase or decrease in total calcium
* Often increased total
* Normal to low ionised

Potassium
Increased:
* Fluid compartment shift in acidosis
* Decreased urinary output- decreased nephons, bladder rupture, anuria, obstruction

Decreased
* Increased urinary losses
* Decreased foot intake or GI loses

Question 13

What is uraemia?

Answer 13

Clinical syndrome that results of loss of kidney function, involving multiple metabolic derangements

NOT HIGH URAEMIA

Question 14

How is the USG interpreted?

Answer 14

1.030 to 1.080- adequate
* indicates functioning tubules
* Supports dehydration if present

1.012-1.029- moderately conc
* grey area
* May be normal if patient hydrated
* definitely abnormal in dehydration
* rule out extra-renal causes before blaming

1.008-1.012- isothenuria
* same as plasma
* may be normal if drink a lot
* definetely abnormal if dehydrates

1.0-1.008- hypothenuria
* Lower specific gravity than plasma
* Requires functioning nephrons

Question 15

How is proteinuria diagnosed?

Answer 15

Dip stick

Small amounts may be normal

Question 16

What should proteinuria be checked for?

Answer 16

• Location- kidneys or elsewhere (pre/renal/post)
• Persistence
• Magnitude

Question 17

Above what magnitde of proteinuria suggests glomerulopathy?

What are the typical treatment thresholds?

Answer 17

> 2- suggestive of glomerulopathy
0.5 dogs/>0.4 cats- treatment threshold- tubulointersitital problem

Question 18

What can cause a post-renal proteinuria?

Answer 18

• UTI
• Nephrolithiasis
• Tumours of urinary tract

Question 19

What could cause glucosuria with normal serum glucose?

Answer 19

Fanconi’s syndrome
Failure of resorption by tubules

Question 20

What does this sediment examination show?

Answer 20

Left to right
Bacteria
Leucocytes
RBCs

Question 21

What are casts?

Answer 21

• Cylindrical moulds of tubules composed of mucoproteins ± cells
• Occasional hyaline and granular casts may be normal
• Granular, cellular and waxy indicate tubular damage = clinically useful

Usually an acute injury?

Question 22

When should urine be checked for cystals?

What do crystals in urine mean?

Answer 22

Look in fresh urine- not sample from owner

Lots of normal animals have crystalluria- not synonymous with urolithiasis

Question 23

1. What urine crystal is this?
2. What significance do they have?
3. What kind of urine do they form in?

Answer 23

1. Struvite- magnesium ammonium phosphate
2. UTI, urolithiasis or normal
3. Alkaline urine

Question 24

What kind of urine crystal is this?

When does urate form?
When does phosphate form?

Answer 24

Amorphus

Urate- acidic- no clinical significance
Phosphate- alkaline- no clinical significance

Question 25

What crystal are these?
What significance do they have?

Answer 25

Top- calcium oxylate dihydrate
* Can be normal or standing urine

Bottom- calcium oxylate monohydrate
* ethylene glycol toxicosis
* Absence does not rule out

Question 26

What is the significance with ammonium biurate or uric acid?

Answer 26

• Portosystemic shunts
• Liver disease
• Dalmatians

Question 27

What are these crystalls associated with?

Answer 27

Cystine
Associated with metabolic defect in the tubular reabsorption of cystine

Bulldogs

Question 28

What are the following crystals?

Answer 28

Drug metabolites
Bilirubin
Cholesterol

Question 29

What can contaminate urine samples?

Answer 29

• Pollen
• Mucus
• Fat droplets
• Sperm
• Starch from gloves

Question 30

What is normal pH of urine?

Answer 30

6-8

Question 31

What should proteinuria be checked for?

Answer 31

Location, persistence and magnitude

Question 32

What can cause a pre-renal proteinurea?

Answer 32

Systemic inflammation
Haemoglobinaemia
Myoglobinaemia
Bence-jones proteinuria