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Y4 SA - Urogenital > Tests for renal function and integrity > Flashcards

Tests for renal function and integrity Flashcards

1
Q

Which substances do the kidneys work to conserve?

A
  • Water
  • Amino acids/proteins
  • Glucose
  • Bicarbonate
  • Sodium
  • Chloride
  • Calcium
  • Magnesium
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2
Q

Which substances do the kidneys work to excrete?

A

Urea
Creatinine
Potassium
H+ ions
Phosphate
Ketones and lactate

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3
Q

What are the functions of the kidney?

A

Excretion of waste
Control of body fluid balance (volume and composition)
- Electrolytes
- Acid-base
- Blood pressure
Production of hormones

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4
Q

Which hormones are produced by the kidney?

A

Erythropoietin
Calcitriol (active Vit D)
Renin (part of the RAAS)

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5
Q

Name the functional unit of the kidney

A

Nephron

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6
Q

Which structures make up the nephron

A

Glomerulus
PCT
LOH
DCT
CD

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7
Q

Describe the process of glomerular filtration

A
  • Water and solutes move across glomerular capillaries and into the nephron
  • Glomerular filtration in health dependent upon renal plasma flow
  • All blood components except: cells, proteins larger than albumin, most lipoproteins
  • Restricted by size, and to a lesser extent charge
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8
Q

Which blood tests can be used to assess renal function?

A

Biochemistry
- Nitrogenous wastes (urea, creatinine)
- Electrolyte balance (Na, K, Cl, Ca, PO4)
Haematology
Blood gas analysis

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9
Q

Which urine tests can be used to assess renal function?

A

Always: USG, dipstick, sediment
Maybe: UPC ratio (if proteinuria)
Rarely: fractional excretions of electrolytes

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10
Q

In practice GFR is indirectly estimated using?

A

Urea or creatinine

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11
Q

Describe the main features of urea

A

Made in liver from ammonia
Can be reabsorbed
Urea is a good marker for severity of clinical signs

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12
Q

Describe the main features of creatinine

A
  • Produced in muscle in a constant process
  • Filtered by glomerulus, not reabsorbed (this is what makes it a better marker)
  • Concentration depends also on muscle mass
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13
Q

How are the levels of urea and creatinine altered when there is a decreased GFR?

A

Both of these increase if there is a decreased GFR as they are not being filtered out fast enough

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14
Q

What is the main cause of an increase in urea?

A

Decreased GFR

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15
Q

List some possible causes of mild urea increases

A

Upper GI haemorrhage
High protein meal
Recent meal
Catabolism (e.g. fever, corticosteroids)

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16
Q

List the causes of a decreased urea

A
  • Severe liver disease or portosystemic shunt
  • Low protein diet
  • Aggressive fluid therapy
  • PU/PD
  • Young animals
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17
Q

What are the 3 possible causes of increased creatinine?

A

Decreased GFR
High muscle mass (mild increase)
High dietary protein

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18
Q

Decreases creatinine is due to?

A

Reduced muscle mass

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19
Q

Define azotaemia

A

An abnormal concentration of urea, creatinine and other nitrogenous compounds in the blood

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20
Q

What is the cause of pre-renal azotaemia?

A

Due to dehydration or decreased cardiac output: clinical evidence of dehydration and or hypovolaemia – signs of heart failure, shock, etc

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21
Q

How is the USG affected by pre-renal azotaemia?

A

Maximally concentrated urine specific gravity
>1.030 in dogs
>1.035 in cats

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22
Q

How is pre-renal azotaemia treated?

A

Fluid therpay

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23
Q

What is the cause of renal azotaemia?

A

Kidney problem

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24
Q

How is the USG affected by renal azotaemia?

A
  • Isosthenuria (1.008-1.012) when >66% of nephrons lost = same concentration as plasma
  • USG inadequately concentrated (so > 1.012 but <1.030 in dogs and <1.035 in cats)
  • USG falls progressively
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25
Q

What is the cause of post-renal azotaemia?

A

Failure of urine output
Easy to diagnose
Expect hyperkalaemia too

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26
Q

Name two other markers of GFR

A

SDMA = symmetrical dimethyl arginine
Iohexol clearance

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27
Q

Describe SDMA as a GFR marker

A

May be useful for earlier detection of CKD
- Increases with 40% reduction of GFR (75% needed for creatinine)
Value only when creatinine is normal or borderline
Results may be slightly higher in puppies, kittens, and greyhounds

28
Q

How do the levels of phosphorus change when there is kidney disease?

A

Hyperphosphataemia
- Reflection of decreased GFR in species with high dietary phosphorus content

29
Q

Which spp is the exception to hyperphosphataemia in kidney disease?

A

Equine
- tend to be HYPOphosphataemic with decreased GFR
- low dietary phosphorus along with GI losses and increased renal loss

30
Q

How do the levels of calcium change when there is kidney disease?

A

↑ or↓ total calcium - check iCa if available
- Often increased total calcium
- with normal to low ionized calcium

31
Q

How do the levels of potassium change when there is kidney disease?

A

Increased:
- Fluid compartment shift in acidosis
- Decreased urinary output (bladder rupture, obstruction)
Decreased:
- Increased urinary losses (esp. in CKD)
- Decreased food intake or GI losses

32
Q

Does azotaemia mean there is an abnormal renal function?

A

Not always as this can be caused by other things

33
Q

Define uraemia

A
  • Not the same as azotaemia or increased urea.
  • Literally “urine in the blood”
  • Uraemia is the clinical syndrome that results from loss of kidney function, involving multiple metabolic derangements
34
Q

What are the clinical signs of uraemia?

A

Vomiting, anorexia, weight loss, diarrhoea, anaemia, ulcerative stomatitis, muscle tremors, convulsions, coma

35
Q

What is USG a measure of?

A

Solutes in urine

36
Q

Where along the nephron is the USG of urine the same as plasma?

A

Glomerulus
PCT

37
Q

How would you interpret a USG over 1.030 (dogs) and 1.035 (cats)?

A

Adequately concentrated
- Indicates functioning tubules (>2/3) *but cats can trick you
- Supports dehydration if present

38
Q

How would you interpret a USG of 1.012 - 1.029 (dogs) and 1.034 (cats)?

A

Grey area
- May be normal if patient is hydrated
- Is definitely abnormal in dehydration
- Rule out extra-renal causes before blaming the kidney!!!
- Examples: Hypercalcaemia, Addison’s disease, Drugs

39
Q

How would you interpret a USG of 1.008 - 1.012?

A

Same Specific Gravity as Plasma
May be normal if drinks a lot of water
Is definitely abnormal if dehydrated
Rule out extra-renal causes before blaming the kidney

40
Q

How would you interpret a USG of 1.000 to 1.008?

A

Lower Specific Gravity than Plasma
Requires functioning nephrons = clinically useful
- Cushings
- Diabetes
- Hypercalcaemia

41
Q

Is protein in urine normal?

A

Very small amount yes, more than 1+, no

42
Q

Describe dipstick analysis for proteinuria

A

Must be interpreted in light of specific gravity: more significant if low USG

43
Q

Which test should be used after finding high levels of protein on a dipstick test?

A

Urine protein to creatinine ratio test - more accurately quantifies proteinuria

44
Q

How must a proteinuria be classified?

A

By:
- location
- persistence
- magnitude

45
Q

Describe locating the proteinuria

A

Rule out pre- and post-renal causes of proteinuria by examining the haematology and serum biochemistry as well as performing cystocentesis.

46
Q

How can you assess the persistence of a proteinuria?

A

The presence of proteinuria should (ideally) be confirmed by taking three samples, two weeks apart

47
Q

How can you assess the magnitude of a proteinuria?

A

The magnitude of the proteinuria should be confirmed using the UP:C
>2.0 – Suggestive of glomerulopathy

48
Q

List some possible causes of a pre-renal proteinuria

A

Fever
Systemic inflammation
Haemoglobinaemia
Hypoglobinaemia

49
Q

List some possible causes of a post-renal proteinuria

A

UTI
Nephrolithiasis
Tumours of the urinary tract

50
Q

What are the proteinuria treatment threshold levels in dogs and cats?

A

Dogs >0.5
Cats >0.4

51
Q

Describe the main features of a glucosuria

A
  • Not normally present in urine
  • Glucosuria seen with serum glucose above: 10 mmol/l in dogs and 13-16 mmol/l in cats
  • If serum glucose normal, it could be due to failure of resorption by tubules: Renal glucosuria (e.g. Fanconi’s syndrome)
52
Q

WBCs and bacteria seen on a sediment analysis indicate?

A

A urinary tract infection

53
Q

What are casts?

A
  • Cylindrical moulds of tubules composed of mucoproteins +/- cells
  • Occasional hyaline and granular casts may be normal
54
Q

Granular, cellular and waxy casts indicate?

A

Tubular damage = clinically useful!
- Indicate something is going on in the kidney – acute kidney injury

55
Q

When can you look for crystals in urine?

A

Look in fresh urine - don’t look for crystals in a sample an owner brings in
Lots of normal animals have crystalluria - not synonymous with urolithiasis!

56
Q

What are struvite crystals

A

Coffin shape
Magnesium ammonium phosphate
Triple phosphate

57
Q

Describe the significance of struvite crystals

A

Significance:
- UTI
- Urolithiasis
- Or normal
Form in ALKALINE urine
Also in vitro

58
Q

Describe the main features of amorphous crystals

A

Urate
- Acidic pH
- No clinical significance
Phosphate
- Alkaline pH
- No clinical significance

59
Q

Which crystals have a ‘maltese cross’ appearance?

A

Calcium oxalate dihydrate - can form in a standing urine sample

60
Q

Which crystals have a ‘picket fence’ appearance

A

Calcium oxalate monohydrate

61
Q

Are Calcium oxalate monohydrate crystals a significant finding?

A

Yes!
Ethylene glycol (EG) toxicosis
Absence does not rule it out

62
Q

Describe the significance of ammonium biurate or uric acid crystals

A

Portosystemic shunts
Liver disease
Dalmatians

63
Q

Cystine crystals are associated with?

A

Metabolic defect in the tubular reabsorption of cystine
- Bulldogs, other breeds

64
Q

List some possible urine contaminants

A

Pollen
Mucus
Fat droplets
Sperm
Conidia and amorphous debris from free catch
Starch from gloves

65
Q

What is the normal range of urine pH?

A

6-8

66
Q

How can you confirm a bladder rupture from fluid obtained from the abdomen following trauma?

A

Measure creatinine content

Y4 SA - Urogenital (12 decks)

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