Tests for renal function and integrity

Question 1

What is the function of the kidneys?

Answer 1

• Excretion of waste products
• Control of body fluid balance
  -maintenance of water, electrolyte + acid-base balance
  -conservation of nutrients
  -regulation of blood pressure
• Production of hormones
  -erythropoietin
  -calcitriol (vit D)
  -renin

Question 2

What does the kidneys conserve?

Answer 2

• Water
• Glucose
• Amino acids / proteins
• Na+
• Cl-
• HCO3-
• Ca2+
• Mg2+

Question 3

What does the kidneys excrete?

Answer 3

• Urea
• Creatinine
• PO4
• K+
• H+
• NH4+
• Lactate + ketones
• Bilirubin

Question 4

What tests can be done for renal function?

Answer 4

• Blood tests = biochem, haematology, blood-gas analysis
• Urinalysis = USG, dipstick, sediment

Question 5

What is physiology of urea?

Answer 5

• Synthesised in hepatocytes - eliminates excess NH4+ formed in tissues
• Freely passes Glomerular filtration barrier
• Half reabsorbed in PCT rest excreted
• Small proportion excreted in faeces

Question 6

What causes increased urea?

Answer 6

• Decreased excretion - prerenal, renal, postrenal
• Increased production =
  -increased haemorrhage (intestinal)
  -increased proteolysis
  -increased protein intake

Question 7

What causes decreased urea?

Answer 7

• Decreased synthesis =
  -liver insufficiency / PSS
  -Decreased protein intake
  -Urea cycle enzyme deficiencies
• Increased excretion = any cause of polyuria

Question 8

What is physiology of creatinine?

Answer 8

• Produced from creatine degradation in muscles
• Freely passes GF barrier
• not reabsorbed = more accurate to measure than urea

Question 9

What causes increased creatinine?

Answer 9

• Decreased excretion = prerenal, renal, postrenal
• Increased production =
  -high muscle mass
  -increased protein intake

Question 10

What causes decrease in creatininine?

Answer 10

• Decreased production = reduced muscle mass

Question 11

What is azotaemia?

Answer 11

• Increase in nonprotein nitrogenous compounds in the blood

Question 12

What causes prerenal azotaemia? CS? USG? Tx?

Answer 12

• Due to reduced renal blood flow
  -hypovolaemia / decreased CO = decreased GFR = decreased clearance
• CS = dehydration +/or hypovolaemia
• USG = >1.030 in dogs,
  -USG >1.035 in cats
• Tx = fluid therapy

Question 13

What causes renal azotaemia? USG?

Answer 13

• Due to kidney disease (loss of 75% of nephron function)
• USG = <1.030 in dogs
  -USG <1.035 in cats
  -Usually isothenuria = 1.008-1.012

Question 14

What causes post renal azotaemia? USG? Dx?

Answer 14

• Urinary tract obstruction
• Leakage of urine within body
• USG varies
• Dx = hyperkalaemia
  -Creatinine conc higher in peritoneal fluid than blood

Question 15

What test can be used for early detection of CKD?

Answer 15

Increased SDMA (symmetric dimethylarginine)
-With 40% reduction in GFR
-(compared to creatinine 75% loss of GFR)

Question 16

What neoplasms can be associated with increased SDMA?

Answer 16

Lymphoma

Question 17

What would happen to phosphorus + calcium with azotaemia?

Answer 17

• Hyperphosphataemia = decreased renal clearance of plasma P
• Calcium - may decrease, increase or stay normal =
  -Decreased formation of VitD
  -Increased Ca bound to nonprotein anions
  =Measure free (ionised) Ca = normal/decreased

Question 18

What would happen to potassium with azotaemia?

Answer 18

• Increased =
  -decrease renal excretion
  -redistribution between intracellular + extracellular compartments
• Decreased =
  -Increased urinary loss - PU
  -Increased GI loss - vomiting/diarrhoea
  -Decreased dietary intake - anorexia

Question 19

What would happen to pH, amylase + lipase with azotaemic animals?

Answer 19

• Decreased pH = decreased renal excretion of H+
• Increased amylase + lipase =
  -Decreased renal excretion + inactiviation

Question 20

What is uraemia?

Answer 20

• Urine in blood
• Clinical syndrome = vomiting, anorexia, weight loss, diarrhoea, anaemia, muscle tremors, convulsions, coma, ulcerative stomatitis

Question 21

What should be checked on physical exam of urine?

Answer 21

• Colour - normal = yellow/amber
  -red/brown = RBCs, HGB, myoglobin
• Clarity - clear / mildly turbid
  -cloudy = cells, crystals, bacteria
• Solute conc - USG, Freezing-point osmometry (gold standard)

Question 22

What can cause hyposthenuria? (lower SG than plasma)

Answer 22

• Problem with production of / response to ADH
  -need functioning nephrons

Question 23

What can cause pre-renal proteinuria?

Answer 23

• Systemic inflammation
• Haemoglobinaemia
• Myoglobinaemia
• Bence-Jones proteinuria

Question 24

What can cause post-renal proteinuria?

Answer 24

• Pyuria
• Haematuria

Question 25

What should be done if renal proteinuria? When would you treat?

Answer 25

• UPCR (urine protein creatinine ratio)
• Treat = UPCR >0.5 in dogs
  -UPCR >0.4 in cats
• UPC >2 = glomerular disease

Question 26

If glucosuria is not due to hyperglycaemia, what is the cause?

Answer 26

• Defective reabsorption by damaged / abnormal proximal tubules
• Fanconi syndrome, proximal tubular toxicosis, ischaemia

Question 27

What can cause haem in urine?

Answer 27

• Haematuria = haemorrhage into urogenital tract
• Haemoglobinuria = intravascular haemolysis
• Myoglobinuria = myocyte damage / necrosis

Question 28

What can cause erythrocytes in urine sediment? (haematuria - haemorrhage)

Answer 28

• Pathological haemorrhage = UTI, urolithiasis, neoplasia, coagulopathy
• Iatrogenic haemorrhage = during cystogentesis / catheterisation
• Oestrus

Question 29

What can cause leukocytes in urine sediment (pyuria)?

Answer 29

• UTI = septic (bacteria, fungi), non-septic (urolithiasis, neoplasia)
• Genital tract inflammation = prostatitis, vaginitis

Question 30

What can cause epithelial cells in urine sediment?

Answer 30

• Neoplasia
• Inflamed / hyperplastic mucosa
• Sometimes healthy animals

Question 31

What are different casts in urine sediment?

Answer 31

• Hyaline casts → primarily with glomerular proteinuria
• Epithelial casts → active tubular degeneration or necrosis
• Granular casts → tubular degeneration, necrosis or inflammation
• Leukocyte casts → inflammation involving renal tubules
• Erythrocyte casts → glomerular or tubular haemorrhage
• Waxy casts → primarily with chronic renal disease

Question 32

What are different crystal s in urine sediment?

Answer 32

• Struvite = healthy animals, UTI, urolithiasis
• Calcium phosphate = healthy, urolithiasis
• Calcium oxalate dihydrate = healthy, urolithiasis, hypercalciuria, hyperoxaluria
• Calcium oxalate monohydrate = hypercalciuria = ethylene glycol toxicity
• Cystine = cystinuria
• Amorphus = healthy animals