Clinical Pathology: Tests for Renal Function and Integrity Flashcards
What are the functions of the kidneys?
- Excretion of waste
- Control of body fluid balance- electrolytes, acid-base, blood pressure
- Production of hormones- erythropoetin, calcitriol, renin
What do nephrons excrete?
- Urea
- Creatinine
- K+
- H+
- PO4
- Ketones and lactate
What are the recommended tests for renal function?
Blood tests
* Biochemistry- urea creastine, electrolyte balance
* Haematology
* Blood gas analysis
Urinalysis
* Always- USG, dipstick, sediment
* Maybe- UPC ratio
* Rarely- fractional excretions
How can GFR be estimated?
Urea and creatinine
urea made in liver from ammonia
Creatinine- produced in a muscle, filtered by glomerulus
Iohexol- rarely done
What can cause an increase and decrease in urea?
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
What can cause an increase or decrease in creatinine?
Increase:
* Decreased GFR
* High muscle mass
* High protein diet
Decrease:
* Reduced muscle mass
What can cause pre, renal, and post renal azotaemia?
Pre-renal
* hypovolaemia, shock, heart failure- dehydration/decreased CO
Renal- chronic or acute
Post-renal- urethral obstruction, urinary tract rupture
What is the maximally concentrated urine specific gravity in dogs and cats?
1.030 in dogs
1.035
If urine above this- urine has been concentrated
At what % of nephrons are lost for renal azotaemia?
75%
What are other markers of GFR?
- SDMA- symmetrical dimethyl arginine
- Iohexol clearance
What are the electrolyte changes in kidney disease?
- Hyperphosphataemia- horses go hypo
- Calcium
- Potassium
How is calcium and potassium affected with kidney disease?
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
What is uraemia?
Clinical syndrome that results of loss of kidney function, involving multiple metabolic derangements
NOT HIGH URAEMIA
How is the USG interpreted?
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
How is proteinuria diagnosed?
Dip stick
Small amounts may be normal
What should proteinuria be checked for?
- Location- kidneys or elsewhere (pre/renal/post)
- Persistence
- Magnitude
Above what magnitde of proteinuria suggests glomerulopathy?
What are the typical treatment thresholds?
> 2- suggestive of glomerulopathy
0.5 dogs/>0.4 cats- treatment threshold- tubulointersitital problem
What can cause a post-renal proteinuria?
- UTI
- Nephrolithiasis
- Tumours of urinary tract
What could cause glucosuria with normal serum glucose?
Fanconi’s syndrome
Failure of resorption by tubules
What does this sediment examination show?
Left to right
Bacteria
Leucocytes
RBCs
What are casts?
- 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?
When should urine be checked for cystals?
What do crystals in urine mean?
Look in fresh urine- not sample from owner
Lots of normal animals have crystalluria- not synonymous with urolithiasis
- What urine crystal is this?
- What significance do they have?
- What kind of urine do they form in?
- Struvite- magnesium ammonium phosphate
- UTI, urolithiasis or normal
- Alkaline urine
What kind of urine crystal is this?
When does urate form?
When does phosphate form?
Amorphus
Urate- acidic- no clinical significance
Phosphate- alkaline- no clinical significance
What crystal are these?
What significance do they have?
Top- calcium oxylate dihydrate
* Can be normal or standing urine
Bottom- calcium oxylate monohydrate
* ethylene glycol toxicosis
* Absence does not rule out
What is the significance with ammonium biurate or uric acid?
- Portosystemic shunts
- Liver disease
- Dalmatians
What are these crystalls associated with?
Cystine
Associated with metabolic defect in the tubular reabsorption of cystine
Bulldogs
What are the following crystals?
Drug metabolites
Bilirubin
Cholesterol
What can contaminate urine samples?
- Pollen
- Mucus
- Fat droplets
- Sperm
- Starch from gloves
What is normal pH of urine?
6-8
What should proteinuria be checked for?
Location, persistence and magnitude
What can cause a pre-renal proteinurea?
Systemic inflammation
Haemoglobinaemia
Myoglobinaemia
Bence-jones proteinuria
