Approach to PU/PD

Question 1

Define polyuria

Answer 1

> 50ml/kg/day of urine

Question 2

define polydipsia

Answer 2

> 100ml/kg/day intake (dogs)
50ml/kg/day (Cats)

Question 3

what are the main differentials for primary polydipsia

Answer 3

centrally mediated disease (neoplasia, endocrine effects, compensating for losses)
OR
physiology ( toxicity, exercise, high temps)

Question 4

what does ADH do

Answer 4

increases aquaporin density and increases reabsorption from tubules.

Question 5

what is osmotic diuresis

Answer 5

if urine contains solutes above normal values (e.g. glucose in diabetes mellitus) this ‘draws’ water into the tubules increasing output.

Question 6

what is medullary solute washout

Answer 6

loss of solutes from the medulla, also leads to a concentration gradient and osmotic water loss.

Question 7

how can increased GFR lead to polyuria

Answer 7

hypertension will lead to increased filtration in excess of the kidneys resorptive capability.

Question 8

Is primary nephrogenic diabetes insipidus common

Answer 8

No rare

Question 9

what are the 2 substances that commonly cause osmotic diuresis

Answer 9

glucose
sodium

Question 10

describe Fanconi’s syndrome

Answer 10

Proximal tubular disease and loss of glucose, but amino acids, bicarb, electrolytes, lactate, etc.- basically animasl looses ability to reabsorp anything

Question 11

List 2 things that can cause reduced medullary/interstitial tonicity

Answer 11

low protein diet
medullary washot

Question 12

what is a Phaeochromocytoma

Answer 12

Catecholamine producing tumour of the adrenal gland i.e. adrenaline
RARE

Question 13

If you see signs of dehydration in animal that is PU/PD what is most likely cause

Answer 13

primary polyuria

Question 14

If you see a USG with >1.030 with normal hydration in PU/PD patient what should you think

Answer 14

normal- owner wrong
or
primary polydipsia driving intermittent polyuria-

Question 15

If you see a USG with >1.030 with dehydration what should you think

Answer 15

animal is normal and dehydrated
OR
check for:
- glucosuria- diabetes mellitus
- Fanconis
- renal tubular glycosuria

Question 16

If you see a USG with <1.030 with normal hydration what should you think

Answer 16

Consider primary polydipsia again, but consistently present.
means that they are pushing more fluid through kidneys

Question 17

If you see a USG with <1.030 with dehydration what should you think

Answer 17

Consider primary polyuria and intrinsic renal disease or extrinsic disease affecting renal function.

Question 18

If you see a USG with <1.006 (Hyposthenuria what should you think

Answer 18

Diabetes insipidus
primary polydipsia
hypercalcemia
hyperadrenocorticism

Question 19

what is considered active dilution by kidneys

Answer 19

<1.006 USG

Question 20

what do you do if you suspect primary polydipsia

Answer 20

Could this just be physiological
Toxin exposure
GI losses

rule out 3rd space loss- POCUS

check fro haem and biochem- look for endocrine and osmolarity changes

Question 21

describe how to work out osmalility of blood

Answer 21

(Na + glucose + BUN) x 2 = osmolality
all values straight from biochem

Question 22

what is the normal osmalalility of blood

Answer 22

dog 290-310
cat 308-335

Question 23

what is azotaemia

Answer 23

elevated urea and creatinine

Question 24

what is warning sign for a phaeochromocytoma

Answer 24

inappropriate hypertension
because it —> Produces adrenaline —> vasoconstricts peripheral vessels —-> increasing central blood pressure

Question 25

describe what causes pre-renal azotaemia

Answer 25

fluid loss i.e. haemoconcentration and reduced renal blood flow (eventually becomes renal also due to renal hypoxia) give fluids

Question 26

what can cause post-renal azotaemia

Answer 26

obstruction or uroabdomen

Question 27

why is post renal azotaemia dangerous

Answer 27

Hyperkalaemia can develop rapidly---> bradycardia

Question 28

what can cause renal azotaemia

Answer 28

AKI or chronic renal failure

Question 29

describe the difference in phosphorus between AKI and CKD

Answer 29

AKI- – Phosphorous increase is marked. CKD- Phosphorous increase is more moderate, and consistent with the creatinine elevation

Question 30

describe how to tell the difference between AKI and CKD

Answer 30

phosphorus clinical signs CKD- 2/3rd renal mass loss anaemia- CKD- due to reduced EPO production

Question 31

what does water deprivation test differentiate between

Answer 31

primary polydipsia, central diabetes insipidus and nephrogenic diabetes insipidus.

Question 32

what do you see with water deprivation test with primary polydipsia

Answer 32

USG improves with just water deprivation

Question 33

what do you see with water deprivation test with central diabetes insipidus

Answer 33

USG improves with vasopressin (ADH)

Question 34

what do you see with water deprivation test with nephrogenic diabetes insipidus

Answer 34

USG never improves

Question 35

which is more commonly the primary issue, polyuria or polydipsia

Answer 35

polyuria

Question 36

what can cause primary polyuria

Answer 36

Intrinsic renal issue or extrinsic effect on kidneys -ADH decrease osmotic diuresis medullary solute washout interstitial tonicity reduction increased GFR CKD AKI

Question 37

what is interstitial tonicity reduction

Answer 37

reduced concentration gradient across the interstitium

Question 38

what can cause a decrease in ADH

Answer 38

no ADH production - central diabetes insipidus OR reduced ADH sensitivity - nephrogenic diabates insipidus

Question 39

what is central diabetes insipidus

Answer 39

no ADH production or release

Question 40

what is nephrogenic diabetes insipidus

Answer 40

reduced ADH sensitivity or response

Question 41

List some common causes of secondary nephrogenic diabetes insipidus

Answer 41

cushings Addisons hyperthyroidism pyometra hypercalcaemia drugs

Question 42

what can cause a post obstructive diuresis

Answer 42

blocked cats

Question 43

what diagnostic test distinguishes between primary PU or PD

Answer 43

USG

Question 44

what does a low osmolality indicate

Answer 44

primary polydipsia

Question 45

List some diagnostic tests to look for a PD cause

Answer 45

history POCUS bloods neuro exam

Question 46

how can we identify renal azotaemia

Answer 46

USG will be isosthenuric, electrolyte disturbances are likely present

Question 47

why is the water deprivation test controversial

Answer 47

if you do the test and your animal is polyuric, not polydipsic, it will die

Question 48

how can you differentiate between psychogenic polydipsia and diabetes insipidus

Answer 48

modified water deprivation test and ADH administration

Question 49

What are the possible mechanisms behind primary polyuria?

Answer 49

ADH or its receptor, Osmotic diuresis, Medullary solute washout Interstitial tonicity reduction increased GFR

Question 50

List the 5 main differentials for polyuria caused by reduced ADH sensivity/response?

Answer 50

Cushings addisons hyperthyroidism pyometra hypercalcaemia

Question 51

What are the main differentials for polyuria caused by osmotic diuresis?

Answer 51

Diabates Mellitus post-obstructive diuresis- e.g. blocked cats Addison's result of diuretics

Question 52

What disease is common in Basenjis relating to glucose diuresis causing a proximal tubular disease?

Answer 52

Fanconi's syndromes

Question 53

What do we want to look for on clinicial exam with the PU/PD patient?

Answer 53

Body condition signs of dehydration neuro-signs dermatological conditions signs of other body systems

Question 54

Why is it important to do a POCUS with a PU/PD patient with suspected primary PD?

Answer 54

Rule out third space loss

Question 55

What next steps would we undertake with a PU/PD patient with suspected primary PU?

Answer 55

Triage if needed, POCUS, urinalysis, biochem and haem, bp, further imaging +/- FNA/renal biopsy

Question 56

How do we rule out pre-renal azotaemia

Answer 56

give fluids and see if urea and creatinine restore to normal

Question 57

What is the top differentials for pre-renal azotaemia

Answer 57

Addisons

Question 58

How do we diagnose an obstruction or uroabdomen?

Answer 58

POCUS to check for blockages or free fluid

Question 59

Why can CKD result in non-regenerative anaemia?

Answer 59

Due to damage, kidneys produce less EPO (erythropoietin) = less RBC are produced`

Question 60

what do you when performing a water deprivation test

Answer 60

over 3-5days you can gradually restrict water and then complete removal of water until 5% dehydration is achieved. If doesn't improve give ADH (vasopressin).