Polyuria

Question 1

What is the difference between polyuria and high urinary frequency and how do you differentiate between the 2 clinically?

Answer 1

In both, will be passing urine more often than before.

• polyuria - passing abnormally large volumes of clear urine each time
• high urinary frequency - volume voided each time will be normal or reduced

collect 24 hour urine sample

Question 2

What are Dx of polyuria?

Answer 2

ENDOCRINE:
Diabetes Mellitus
Diabetes insipidus
Hyperthyrodism

HEART FAILURE

ELECTROLYTE IMBALANCE:

• hypercalcaemia
• hypokalaemia

MEDICATION:
Diuretics, caffeine, alcohol, lithium

PSYCHIATRIC
• Psychogenic polydypsia

Renal failure
hypercalcaemia

BONE metastases - hypercalcaemia

Steroids and Cushing’s cause polyuria by causing DM

Question 3

What questions will help you narrow down the cause of polyuria?

Answer 3

What is the temporal pattern of urine output?
Any fatigure, weight loss, recurrent infections? suggests diabetes
Any LUTS? frequency, urgency, hesitance, terminal dribbling, incomplete voiding
Any pain, change in urine frequency, colour, smell? UTI
Drug history- diuretics
Family history - DM

Question 4

What will you ask about on PMHx of polyuria?

Answer 4

RENAL
History of renal problems or triggers of renal problems? vasculitides, urinary retention,

hypertension

CANCER:
Older patients: ask about cancer and known bony involvement

PSYCHIATRIC
Any psychiatric disorders

Question 5

What should you look for in the drug history of someone with polyuria?

Answer 5

Diuretics, lithium (causes nephrogenic DI)

Question 6

What should you look for in the family history of someone with polyuria?

Answer 6

Diabetes, any cancers

Question 7

Why do we not need to urinate when we sleep?

Answer 7

at night, the kidneys concentrate the urine in order to retain fluid

Question 8

What is nocturia a sign of?

Answer 8

(in absence of other causes such as BPH) early sign of loss of ability to concentrate urine.

Question 9

What are simple tests in someone with polyuria? What are they used to detect/exclude?

Answer 9

Capillary blood glucose (DM) and urinalysis (UTI + glucose and ketonuria for DM)

Question 10

What are further Ix for polyuria?

simple tests are capillary blood glucose and urinalysis

Answer 10

Fasting glucose, urine osmolality, electrolytes (primary polydypsia will have hypOnatremia), urea, creatinine, EGFR, calcium and TFTs

Question 11

What are the two different mechanisms that can cause polyuria and how do they reflect in the urine osmolality

Answer 11

Inability to reabsorb solutes - remain in the urine and keep water with them -> high urine osmolality
Inability to reabsorb water (can be due to ADH deficiency) -> low urine osmolality

Question 12

how will the results of electrolytes differ in someone with polydipsia to the other pathologies of polyuria?

Answer 12

polydipsia - serum sodium will be diluted due to excessive water intake
other pathologies - will be high because of dehydration

Question 13

Why do we test for urea, creatinine and eGFR in patients with polyuria?

Answer 13

to rule of out chronic kidney disease

Question 14

Polyuria. No DM. Urine osmolality low and normal serum sodium.
What is the differential?

Answer 14

diabetes insipidus

Question 15

What are the types of diabetes insipidus and whitest can be done to differentiate between then.

Answer 15

Cranial and nephrogenic
cranial - problem with the posterior pituitary (low/no ADH secretion). kidneys are normal
nephrogenic - problem with the kidneys, not sensitive to ADH

water deprivation test - give desmopressin.

• cranial DI - can now concentrate the urine
• nephrogenic - no change in urine concentration

Question 16

overall, give the order of investigating someone with polyuria

Answer 16

• plasma glucose (to rule our DI)
• if normal, urine osmolality (if normal, consider causes of diuresis)
• if high, plasma sodium (if low -> polydipsia)
• if normal, water deprivation test —> will help categorise type of DI

Question 17

What are causes of cranial and nephorgenic DI?

Answer 17

Cranial- pituitary tumours, cranipharyngiomas, trauma, mets, vascular lesions, meningitis

Nephrogenic- pyelonephritis, hypokalemia, hypercalcemia, lithium drugs, hydronephrosis, inherited

Question 18

What is management of cranial DI?

Answer 18

Adequate fluid intake, investigate cause, give ADH replacement

Question 19

What are the WHO criteria for the diagnosis of diabetes mellitus?

Answer 19

either:

• fasting plasma glucose over 7.0
• glucose tolerance test (taken 2 hours after indigestion 75g of glucose)- plasma glucose over 11.1

must be met on two separate occasions or on one occasion with symptoms