Approach to PU PD

Question 1

Define polyuria.

Answer 1

Urine production >50 ml/kg/day

Question 2

Define polydipsia.

Answer 2

Water intake >100 ml/kg/day

Question 3

Define isosthenuria.

Answer 3

USG 1.008-1.012

Question 4

Define hyposthenuria.

Answer 4

USG 1.001-1.007

Question 5

Define minimally concentrated.

Answer 5

USG < 1.030 for dogs and <1.035 for cats

Question 6

Define dysuria.

Answer 6

Difficult urination

Question 7

Define stranguria.

Answer 7

Straining to urinate

Question 8

Define pollakiuria.

Answer 8

Increase frequency of urination

Question 9

What are differentials for hyposthenuria?

Answer 9

Hyperadrenocorticism
E. coli infection
Psychogenic polydipsia
Central diabetes insipidus
Nephrogenic diabetes insipidus
Hepatic insufficiency

Question 10

What is ADH released in response to?

Answer 10

Increased plasma osmolality and volume depletion

Question 11

What is the mechanism for pu/pd with diabetes mellitus? How would you diagnose it?

Answer 11

Osmotic diuresis due to glucosuria
Dx: blood glucose, urine glucose

Question 12

What is the mechanism for pu/pd with renal failure? How would you diagnose it?

Answer 12

Osmotic diuresis of remnant nephrons + structural disruption of medullary concentration gradient
Dx: BUN, creatinine, SDMA, urinalysis

Question 13

What is the mechanism for pu/pd with bacterial pyelonephritis? How would you diagnose it?

Answer 13

Renal parenchymal damage + E. coli endotoxin competes with ADH on renal tubules
Dx: Urine culture, abdominal ultrasound, excretory urogram

Question 14

What is the mechanism for pu/pd with hypercalcemia? How would you diagnose it?

Answer 14

Inhibits binding of ADH to receptors on renal tubules
Dx: Serum or plasma calcium

Question 15

What is the mechanism for pu/pd with hyperadrenocorticism? How would you diagnose it?

Answer 15

Glucocorticoids inhibit ADH release and inhibit effect of ADH on renal tubules
Dx: LDDST, ACTH stimulation test, urine cortisol:creatinine ratio

Question 16

What is the mechanism for pu/pd with hyperthyroidism? How would you diagnose it?

Answer 16

Increased medullary blood flow + psychogenic
Dx: serum T4

Question 17

What is the mechanism for pu/pd with hepatic insufficiency? How would you diagnose it?

Answer 17

Loss of medullary concentrating gradient (low urea), possibly psychogenic
Dx: Chem panel, bile acids, blood ammonia, abdominal imaging

Question 18

What is the mechanism for pu/pd with pyometra and E. coli septicemia? How would you diagnose it?

Answer 18

Endotoxin competes with ADH binding sites on renal tubules
Dx: History, CBC, abdominal imaging, cultures

Question 19

What is the mechanism for pu/pd with post-obstructive diuresis? How would you diagnose it?

Answer 19

Osmotic diuresis due to retained solutes (especially urea)
Dx: history, urine output

Question 20

What is the mechanism for pu/pd with hypoadrenocorticism? How would you diagnose it?

Answer 20

Mineralocorticoid deficiency results in sodium loss + renal medullary washout
Dx: Serum Na+ and K+, ACTH stimulation test

Question 21

What is the mechanism for pu/pd with diabetes insipidus? How would you diagnose it?

Answer 21

Primary: decreased ADH production
Nephrogenic: defect in renal response to ADH
Dx: modified water deprivation test and diagnosis of exclusion