Polyuria Flashcards
What does polyuria and high urinary frequency have in common?
passing urine more often that before
How is polyuria different from high urinary frequency?
pass abnormally large volumes of clear urine each time
How do you check if it is true polyuria?
collecting 24hr urine sample (>3L = polyuria) - usually hard to rely on patient
What are differential diagnosis for polyuria?
- Diabetes mellitus (T1 or T2)
- Diuretics (e.g. diuretic medication, caffeine, alcohol, lithium)
- Heart failure
- Hypercalcaemia
- Hyperthyroidism
- Primary polydipsia
- Hypokalaemia
- Hyperuricaemia
- Diabetes insipidus (cranial or nephrogenic)
How can chronic renal failure and hypercalcaemia (e.g. due to bone metastases) cause polyuria?
by inducing nephrogenic diabetes insipidus
Why can steroids and Cushing’s syndrome cause polyuria?
by causing diabetes mellitus
What questions do you ask patient to help narrow down differential?
- Temporal pattern of urine output
- Fatigue, weight loss, recurrent infections
- Lower urinary tract symptoms
- Pain frequency, change in urine colour and smell
- PMHx
- DHx
- FHx
What do you ask about temporal pattern of urine output?
no of times day and night especially nocturia
What does nocturia (in absence of other causes e.g. BPH) suggest?
one of earliest signs of loss of concentrating ability - makes primary polydipsia less likely
What would fatigue, weight loss, recurrent infections and polyuria suggest?
DM
What are examples of lower urinary tract symptoms?
- frequency
- urgency
- hesitancy
- terminal driblling
- incomplete voiding
What would symptoms of lower urinary tract suggest?
- pathology of bladder or outflow tract
- e.g. prostatism (men)
- detrusor instbaility and prolapse (women)
- not really polyruia
Why do you ask about pain frequency, change in urine colour and smell with polyuria?
suggestive of UTI, which could cause increased frequency but not polyuria
What PMHx do you ask about with polyuria?
- Hx renal problems e.g vasculitides, hypertension, chronic urinary retention
- Older patients, cancer (bony mets, hypercalcaemia)
- primary polydipsia in psychiastric disorders
What DHx do you ask about with polyuria?
- diuretic are potential and obvious cause of polyuria
- recent changes in medication or new over counter drugs
- lithium
Why can lithium cause polyuria?
inducing nephrogenic diabetes insipidus
What FHx do you ask about polyuria?
- hereditary component to DM and some forms of cancer
2. familial forms of diabetes inspidus (nephorgenic and cranial) present early in life
What GP tests must you request for polyruia?
- Cap blood glucose
2. Urinalysis with dipstick
Why do you do a cap glucose?
check for DM
Why do you do a urinalysis for polyuria?
- exclude UTI
2. see if glucosuria and ketonuria other signs of DM
What other tests may you request for polyuria?
- Fasting plasma glucose
- Urine osmolarity
- Electrolytes
- Urea, creatinine and eGFR
- Serum calcium
- Thyroid function
Why/When do you do fasting plasma glucose?
- if cap glucose is near upper limit or above normal
2. to exclude DM and calculate serum osmolarity
What could lead to a high osmolality and volume?
inability to reabsorb solutes by the kidneys, solutes remain in urine and keep water with them
What could lead to a low osmolality and volume?
inability to reabsorb water due to distal tubule pathology of deficient ADH pathway
What would electrolyte levels be like in primary polydipsia?
serum sodium will be dilute
What would electrolyte levels be like in other polyuria pathologies?
serum sodium concentrated
Why do you need to measure potassium?
calculate serum osmolarity
Why do you measure urea, creatinine and eGFR for polyuria?
help exclude chronic kidney failure
Why do you measure serum calcium in polyuria?
exclude hypercalcaemia
Why do you measure thyroid function in polyuria?
exclude hyperthyroidism
What are the 2 types of diabetes inspidius?
- Cranial/Central
2. Nephrogenic
What is the cranial/central inspidous?
- ADH secretion either reduced or absent due to defect in hypothalamic-pituitary axis
- Signal to kidneys to concentrate the urine is weak or absent
What are the causes of cranial inspidus?
- head injury
- pituitary tumours
- craniopharyngiomas or metastases
- surge5y
- vascular lesion
- metastasis
What is nephrogenic insipidus?
kidneys become less sensitive to ADH so do not respond to signals to concentrate the urine
What are causes of renal damage for nephrogenic insipidus?
- low potassium
- high calcium
- lithium
- pyelonephirits
- hydronephorisis
- may be inherited
What is a water deprivation?
distinguish between two times
What is the process of a water deprivation test?
- Patient is fluid restricted
- Normal person ADH released to concentrate urine but in DI, urine dilute
- Desmopressin given, cranial DI will be able to concentrate urine but not nephrogenic
What should you do before a water deprivation test?
ensure true polyuria with 24hr urine
Why is a water deprivation potentially dangerous?
if DI as deprivation can cause hypovolemia so patients wieghed through
When will the water deprivation test be stopped?
if body weight loss >3%
What would polyuria + raised plasma glucose suggest?
DM
What would polyuria + normal plasma glucose + normal urine osmolarity >300mOsm/L suggest?
solute diuresis (drugs, contrast agent, urea)
What would polyuria + normal plasma glucose + low urine osmolarity <250mOsm/L + low serum sodium suggest?
psychogenic polydyspia
What would polyuria + normal plasma glucose + low urine osmolarity <250mOsm/L + normal serum sodium suggest?
diabetes insipidus (desmopressin test to determine type)
What is the management for cranial diabetes inspidus?
- Adequate fluid intake
- Investigation of underlying cause
- Replacement ADH
When would you do investigation of underlying cause for CDI?
- when no obvious cause is present (e.g. intercranial surgery)
- MRI head
When do you give replacement ADH?
if no reversible cause of cranial DI (e.g. pituitary tumour) patients need to take replacement ADH for life
What medications do you use in nephrogenic but not cranial DI?
e.g. chlorpropamide, carbamazepine
