Urinary

• Normal horse urine is cloudy (but can be clear) and this is not an issue (due to high mucous and calcium). It is also yellow in colour
• Incontinence can occur due to a urological disease but also neurological!
• dental tartar can be present in horses with chronic azotaemia
• evidence of incontinence include urine dropping and scalding (alopecia that smells of urine)
• horses are hindgut fermenters which mean they can produce BUN in other ways hence it is harder to interpret than in cats and dogs
• BUN : Creatinine ratio is higher in acute cases of urinary disease

  • BUN takes longer to increase than creatinine
• • Hyposthenuria - less than 1008
  • Isosthenuria - 1008-1014
  • Hypersthenuria - greater than 1014
  • Normal adult horse 1025-1045
• Hyperkalaemia, hyponatremia and low chloride can be seen in urinary disease
• low albumin can indicate a protein losing nephropathy
• Muscle enzymes (CK & AST) indicates myopathies but this is normally based on assessing the pigment of the urine
• Glucose in urine means more water is lost and hence dehydrates the horse leading to PU/PD
• Horse urine is often alkaline (8-9)
• cystocentesis is not done in horses, urine samples are obtained either via free catch or catheterization
• What is Azotaemia?

  an increase in creatinine and urea that occurs when kidneys have been damaged by disease or an injury
• true or false, serum BUN is more sensitive than Serum Creatinine for the detection of a decrease in GFR?

  false
• true or false, In prerenal azotaemia USG will likely be increased (hypersthenuria)?

  true
• horses with intrinsic renal azotaemia will be isosthenuric
• in horses the BUN/Creatinine ratio is more reliably used to differentiate which of the following

  1. Prerenal from renal azotaemia
  2. Chronic Renal Failure from Acute Kidney Injury (AKI or ARF)

  chronic renal failure from acute kidney injury
• Hypercalcemia & hypophosphatemia are most seen in horses with which of the following

  1. Acute kidney injury AKI (or ARF)
  2. Chronic renal failure (CRF) - however could also be acute
  3. Renal Tubular Acidosis (RTA)

  CRF
• One or two plus of protein is normal in alkaline urine
• klebsiella is likely a contaminant in equine urine
• Is azotaemia present in this case?

  no

  
• what is the cause of increased urination in this case?

  This is likely due to an increased water intake due to boredom as she is not being turned out as much. This is psychogenic polydipsia - to confirm need to perform a water deprivation test.

  
• is azotaemia present in this case?

  no

  
• why is BUN high in this case?

  due to an issue with the GI tract

  
• is azotaemia present in this case?

  yes

  
• what type of azotaemia is seen in this case?

  intrinsic renal - oxytetracycline has been given at a high dose and is nephrotoxic. However, there could also be renal damage that has been present since birth.

  
• Foals are often hyposthenuric
• Post-renal azotaemia results from obstruction (urolithiasis) or rupture (uroabdomen) of urinary outflow tracts.
• Post-renal azotaemia is best diagnosed by clinical signs (e.g. frequent attempts to urinate without success or presence of peritoneal fluid due to uroabdomen) and ancillary diagnostic tests (e.g. inability to pass a urinary catheter) as urine-specific gravity results are quite variable. Animals with post-renal azotaemia are usually markedly hyperkalaemia and hypermagnesemia and may have concurrently low sodium and chloride concentrations.
• In acute kidney injury, total calcium is often low and phosphate is high (especially in young horses), whilst in chronic renal failure, hypercalcemia and hypophosphatemia occur (not in all cases as indicated above). Hyperkalaemia is a feature (with low sodium and chloride) of uroabdomen (most common in foals).
• horses with decreased GFR may not always have hyperphosphatemia due to other sources of phosphate elimination such as saliva and the GI tract. In fact, horses with azotaemia due to chronic kidney disease often (but do not always) have high calcium and low phosphate concentrations.
• renal azotaemia is due to decreased function or number of nephrons, resulting in the inability of the remaining or functional glomeruli to adequately filter out nitrogenous waste.
• pre-renal azotaemia is due to decreased blood flow to the kidneys. It can lead to a secondary renal azotaemia due to hypoxia-induced renal injury.
• Acute kidney injury is common in hospitalised horses but most don’t progress to acute renal failure
• AKI can be defined as an increase of greater than 25µmol/L in serum creatinine in 48hrs
• Acute renal failure (ARF) is an advanced decline in glomerular filtration rate (GFR) that occurs over hours or days. The main causes are…

  • Haemodynamic
  • Enterocolitis
  • Haemorrhagic shock
  • Septic shock
  • Coagulopathy
  • Severe intravascular volume deficits
  • Nephrotoxic
  • Antibiotics
  • NSAIDs
  • Myopathy and haemolysis
  • Vitamin D or K3
  • Heavy metals
  • Uncommon causes are
  • Interstitial nephritis
  • Obstructive nephropathy (discussed in pigmenturia - far left)
  • Rare cause include acute glomerulopathies (Immune mediated most commonly)
• Clinical signs of AKI and ARF include…

  • Predisposing disease
  • D+
  • SIRS/MODS
  • Myopathies which are nephrotoxic
  • Colic
  • Fever - not that common
  • More from primary disease
  • Urine output
  • Oliguria, anuria, polyuria
• Fill in the blanks

  A) increased

  B) 1.025

  C) hyponatraemia

  D) hypochloraemia

  
• AKI / ARF patients often need IVFT (intravenous fluid therapy with Hartmann's) for at least 2-4 days

  • Gentle, no need to bolus as this will add too much pressure to the kidneys. Ideally give maintenance or twice maintenance. This helps flush out the kidneys and encourages diuresis

  IVFT becomes complicated when oliguric or anuric in ARF cases. Prognosis depends on the cause.