Clinical Biochemistry 4

Question 1

Normal filtration in the kidney.

Answer 1

Blood in and through a filter unit.
Some stuff filtered incl. sugars, salts, small proteins and various other components.
A lot of this is reabsorbed during course of flow through the kidney and this is mediated by different parts of the kidney.
Mediates acid base status and electrolyte status.

Question 2

Indicators of kidney injury…
1. Nephron loss

Answer 2

1. AKI vs CKD.
   Loss of electrolyte / water regulation (loss of ability to reabsorb).
   – PU/PD, electrolyte derangement.
   Loss acid/base regulation.
   – Metabolic acidosis causing lethargy, inappetance, nausea. (Loss of organ function in extreme cases).
   Accumulation of organic solutes e.g. urea, creatinine (as not being filtered out).
   – uraemia, lethargy, inappetance, V / D (ulceration).
   Hyperphospataemia (accumulation due to not filtered out) / renal secondary hyperparathyroidism (Increase parathyroid hormone levels), increasing calcium levels, and can cause osteoporosis.
   Impaired hormone synthesis.
   – Reduced calcitriol (active form of vitamin D); reduced erythropoietin, causing anaemia
   Hypertension.
   – Body having to push blood through kidneys harder to try and filter as much as they were beforehand, but this damages the kidneys and fine gromerular membranes – it’s a cycle.

Question 3

……
2. Glomerular disease
3. Tubular disease

Answer 3

2. Proteinuria which ranges from mild to severe.
   Severe – Urine protein creatinine ratio of 10-20 w/ normal being <0.5.
   Can be to the point where the body is unable to protein it is losing and ends up accumulating fluid within body cavities.
   Can lost antithrombin as a result, increasing risk of having blood clots.
3. Glucosuria as not reabsorbed back into the blood at tubules. Can cause osmotic diuresis and PU/PD.
   Mild levels of proteinuria.
   Acid base problems.

Question 4

1. What is azotaemia?
2. What could cause azotaemia pre-renally?

Answer 4

1. Where there is an increase in urea and/or increase in creatinine.
2. Pre-renal – due to patient not being fasted at time of sampling (post-prandial).
   – Dehydration.
   – Hypovolaemia.
   – GI haemorrhage (bleeding into gut then digesting the proteins).
   – Breed-related increase in creatinine due to increased protein due to increased muscular levels. e.g. greyhounds, Birman cats.

Question 5

1. What can cause azotaemia post-renally?
2. What is a marker for early reduction in kidney function?
3. What happens if renal azotaemia progresses?

Answer 5

1. Obstruction or rupture.
2. SDMA (Symmetrical Dimethylarginine).
   – Very early marker of reduced kidney function. Seen to start increasing before loss of ability to concentrate urine.
   – Can be increased with some other disease processes too. If mild increases with no evidence of azotaemia, may not act too much on it.
3. Uraemia.

Question 6

What is uraemia?
What does it result from?
What does it cause?

Answer 6

A clinical syndrome that cannot be seen on blood work, resulting from inadequate excretory, regulatory and endocrine function.
Causes lethargy, nausea, vomiting, stomatitis (gums peeling away due to ulcerations), encephalopathy (unaware of environment, disorientated etc), bone pain

Question 7

1. What is pre-renal azotaemia ultimately caused by?

Answer 7

1. Reduced blood flow to the kidney so reduce GFR. (or increased protein catabolism / GI haemorrhage).
   Afferent vessel entering glomerulus starts to narrow down to try and preserve the volume of blood centrally.

Question 8

How does the kidney respond to reduced blood flow (prerenal azotaemia)?

Answer 8

Kidneys will do everything they can to conserve water.
See concentrated urine i.e. USG > 1.030 dog / >1/035 cat.
But not all cases will have conc. urine (due to factors that could impact ability to conc. urine incl. electrolyte disturbances).

Question 9

Renal azotaemia overall cause?

Answer 9

Fewer functional nephrons.
Kidneys unable to conserve water in face of reduced blood flow.
See dilute urine i.e. USG <1.030 dog / <1.035 cat.
Note: this is not the same as dilute urine without azotaemia. This can be normal in the dog.

Question 10

1. Why have we started using SDMA as a marker rather than azotaemia?
2. At what percentage loss of kidneys do we start to see loss of urine concentrating abilities?

Answer 10

1. Azotaemia not a good marker for kidney damage.
   Takes about 2/3-3/4 of kidney loss to start to see urea and creatinine increase.
2. 67-75%.

Question 11

1. What types of obstruction (back pressure) can cause post-renal azotaemia?
2. How does urinary tract rupture cause post-renal azotaemia?
3. How are these conditions identified?

Answer 11

1. Urethral e.g. with urate stones.
   Ureteric (bilateral).
2. Causes urine leakage which is reabsorbed (waste products).
   e.g. uroabdomen (commonly).
   e.g. leakage into retroperitoneal space / hindlimb tissues (less commonly).
   – traumatic or iatrogenic.
3. History, imaging (esp. ultrasound), +/- effusion analysis.

Question 12

What is the gold standard for assessing kidney function?
– disadvantage?

Answer 12

Glomerular filtration rate.
– Laborious – involves giving a drug, seeing how it distributes around the body and then measuring that drug again.

Question 13

What are surrogate markers for GFR?

Answer 13

-Increased urea.
– Breakdown product of ammonia (from GIT) in the urea cycle (liver).
– Production / excretion NOT constant (try to make it constant by fasting patients).
– Urea decreases in hepatic insufficiency/portosystemic shunting, extreme PUPD, low protein diets, in young animals.
- Increased creatinine.
– Breakdown product of muscle (influenced by muscle mass).
–> young (lower) vs well-muscled (higher) e.g. greyhounds and some sports horses.
–> cachectic older cats may have underrepresented creatinine.
– Physiologically increased in foals so not too worried.
- Symmetrical Dimethylarginine (SDMA) increase.
– Independent of muscle mass.
– Independent of food.
– NOT as good as it looks!

Question 14

Important considerations for ruminants and equids?

Answer 14

Urea may be normal in severe kidney disease.
– most urea is excreted via gut.
Urea levels influenced by diet.
Creatinine is much more reliable marker.

Question 15

Other typical changes with reduced GFR.

Answer 15

Hyperphosphataemia.
– Phosphate primarily renally excreted.
Calcium variable
– dependent on many different factors within the kidney. (excretion, absorption etc.)
– Phosphate levels alter calcium levels.
– Typically normal to hypercalcaemia in CKD.
–> Depends on if calcium levels caused CKD or are the consequence of it.
– Typically normal to low in AKI.

Question 16

How does potassium change due to renal changes?

Answer 16

Potassium is dependent on GFR / urine output.
– Anuria / oliguria –> see hyperkalaemia as the kidneys are the main excretion route of potassium.
–> more likely with AKI.
–> also seen in end-stage CKD.
– Aldosterone deficiency / hypoadrenocorticism (Addison’s), see hyperkalaemia.
– Polyuria, see hypokalaemia, trying to conserve water by conserving sodium by exchanging it with potassium in convoluted distal tubules.
–> Compromises ability to concentrate urine.

Question 17

Changes in sodium due to changes in the kidneys?

Answer 17

Dependent on multiple factors but may reflect….
- Volume status
– Hypernatraemia with dehydration.
– Hyponatraemia with overhydration.
- Aldosterone deficiency / hypoadrenocorticism (Addison’s), see hyponatraemia.

Question 18

Urine collection.

Answer 18

• Free catch (mid-flow) – Uripet device / takeaway containers / kidney dish.
• Non-absorbable cat litter.
• Catheterisation.
  – Consciously/sedated in male dogs.
  – Anaesthetised in cats and female dogs.
• Cystocentesis
  – Can be taken blind by palpation or ultrasound-guided.
  – Only sterile method of collection.
  – For bacterial culture.
  – Avoid in patients with no platelets.
  – Avoid in patients with cancers in bladder.

Question 19

1. When should a urine sample be analysed?
2. What is used to analyse USG?
3. Advantages and disadvantages of refrigerating urine sample.

Answer 19

1. Within 1 hour of its collection.
2. Refractometer.
3. • Preserves physical / chemical properties.
     + Slows bacterial overgrowth.
     – Can enhance crystal development which gives a false positive for crystals in the urine.

Question 20

Why would we perform urinalysis?

Answer 20

• Confirm origin of azotaemia.
• Evaluate for disease affecting other / specific regions of the kidney.
• Azotaemia specifically reflects tubular function (globally).
• To evaluate for causes of kidney disease.

Question 21

Why would you see glucose in the urine?

Answer 21

Hyperglycaemia.
– Could be stress associated.
– Could be secondary to DM (Check BG).
– Could be tubular damage (BG remains normal).
–> Fanconi syndrome.
–> Lepto.
–> Toxicity.

Question 22

Why would you see bilirubin in urine?

Answer 22

In dogs – is normal.
In other spp. – is abnormal and reflects hyperbilirubinaemia.
Bilirubin in pee contributes in part to the yellow colour of it.

Question 23

Why would ketones be seen in the urine?

Answer 23

Typically only observed as part of DM (diabetic ketosis / ketoacidosis).
Should evaluate for DM.
Other causes of ketonaemia / ketonuria are rare (e.g. starvation).

Question 24

1. What is hyposthenuria?
2. What is isosthenuria?
3. What is minimally concentrated urine USG?

Answer 24

1. USG <1.008, meaning the urine is actively diluted – kidneys working.
2. USG 1.008-1.012, comparable to plasma, reflective of KD.
3. USG 1.012-1.030/35, partially concentrated.

Question 25

Causes of reduced urine concentration.

Answer 25

Hypercalcaemia Hypokalaemia Hyponatraemia Hyperadrenocorticism Hypoadrenocorticism Hyperthyroidism Liver disease (low urea) Glucosuria e.g. DM, Fanconi. Endotoxins (e.g. pyometra). Drugs e.g. mannitol; phenobarbital; prednisolone. KD (e.g. CKD; lepto.) Young age (short LoH). High salt diet. IVFT. Oral fluid intake > requirements. Many mechs that are multifactorial.

Question 26

Why would you see blood in the urine?

Answer 26

Haematuria -- primary urinary tract disease or coagulopathy. Haemoglobinuria (or myoglobinuria) -- haemolysis (or severe myopathy) or aged sample with haematuria.

Question 27

How can the pH measurement on dip sticks be useful?

Answer 27

When evaluating crystalluria. -- oxylate at lower pH. -- Struvite at higher pH.

Question 28

How can protein measurement on dip stick be used?

Answer 28

As a screening marker. To assess for post-renal causes, then measure UPC (urine protein : creatinine ratio). But is inaccurate as does not take into account how concentrated the urine is. So send off for further measurement if shows a positive.

Question 29

1. Pre-renal proteinuria.

Answer 29

1. Pushing through kidneys too hard and causing blood proteins to be pushed through the glomerular surface. Increased blood proteins. -- Hyperglobulinaemia. -- Haemoglobinuria / myoglobinaemia. Functional -- pyrexia -- post-exercise -- seizure

Question 30

Renal proteinuria.

Answer 30

Intrinsic KD. Kidneys not absorbing proteins as they should at the tubules (mild). Kidneys leaking proteins out e.g. due to damage to glomerular basement membrane (mild to marked).

Question 31

Post-renal proteinuria.

Answer 31

Urinary tract (ureteric, bladder, prostatic, urethral). -- Inflammatory. --> sterile e.g. urolithiasis. --> infectious e.g. UTI. -- Neoplastic disease. -- Haemorrhage into urinary tract.. Or repro related.

Question 32

Why would nitrites and leukocytes be seen on dip stick?

Answer 32

Can be markers of infection. But unreliable -- false positives and false negatives occur. Perform cytology / sediment examination instead.

Question 33

Urine sediment preparation.

Answer 33

Gently mix sample. Transfer standard volume (5ml) to allow sample comparison pre/post centrifuge. Centrifuge at 1500 rpm for 5 mins. Decant supernatant with pipette. -- Leave small amount for resuspension. Re-suspend by flicking tube until well mixed.

Question 34

What is then done with the re-suspended urine?

Answer 34

Pipette onto a clean glass slide. Apply cover slip. Examine under low light (lower condenser, close diaphragm aperture). *Can use stains to enhance what you can see.

Question 35

LOOK AT IMAGES OF TYPES OF URINARY CRYSTALS ON THIS LECTURE TO FAMILIARISE WITH WHAT THEY LOOK LIKE!!!

Question 36

1. What is technical name for struvite crystals? 2. When are these crystals typically seen? 3. When are calcium oxalate dihydrate crystals typically seen? -- what is a different form of calcium oxalate? 4. When are urates typically seen? 5. What are casts?

Answer 36

1. Magnesium ammonium phosphate. 2. Typically seen with high pH or associated with infection. 3. Hypercalcaemia. Can be seen in bichons. -- Calcium oxalate monohydrate. 4. Reduced liver function. 5. Protein plugs that have been sat in the tubules and then been pushed out. -- granular casts can be seen with CKD or post-exertion. -- Hyaline casts can be seen with dehydration or post-exertion. -- Cellular casts can be seen with inflammation, infection or infarction.

Question 37

1. What is seen with cytology if patient has haematuria? 2. What is seen with cytology if patient has infection?

Answer 37

1. Red and white blood cells. 2. White blood cells and rods.

Question 38

1. Order urine collection methods from worst to best for sending off for bacterial culture. 2. Consideration for collecting the urine sample for bacterial culture. 3. If bacteria is found, what should be considered?

Answer 38

1. Floor > non-sterile container > free-catch > catheter > cystocentesis. 2. Collect before administration of any antimicrobials. 3. Is it from UTI or is it subclinical bacteriuria?