Polyuria Flashcards
What is the difference between polyuria and urinary frequency
Both involve passing urine more often than before
Polyuria = abnormally large volumes passed
Urinary frequency = reduced/normal volume
What are the ddx for polyuria
T1DM/T2DM Diuretics HF Hypercalcaemia Hyperthyroidism Primary polydipsia Hypokalaemia
How can chronic renal failure and hypercalcaemia cause polyuria?
How can steroids and Cushings syndrome induce diabetes mellitus
CRF and hypercalcaemia induces nephrogenic diabetes insipidus
Steroids and Cushing’s syndrome induces diabetes mellitus
What diagnosis does nocturia make LESS likely
Primary polydipsia
Fatigue, weight loss and recurrent infections are all features of?
Diabetes mellitus
What may lower urinary tract symptoms (LUTS) - frequency, urgency, hesitancy, terminal dribbling and incomplete voiding indicate?
Pathology of bladder or outflow tract (e.g. prostatism in men, detrusor instability/prolapse in women)
Pain, frequency, change in urine colour and smell all indicate what?
UTI.
UTIs would cause increased urinary frequency, but NOT polyuria
In elderly patients, what is a common cause of polyuria?
History of cancer or bone metastasis, as this increases likelihood of hypercalcaemia which can cause polyuria
Patients with a history of psychiatric disorders may be more likely to have what?
Primary polydipsia
Which drug given in bipolar disorder can cause nephrogenic diabetes insipidus
Lithium
Which investigations should be done in someone with polyuria
- Capillary blood glucose
- Urinalysis - exclude UTI (UTIs give urinary frequency not polyuria), glucosuria and ketonuria are signs of DM
- Fasting plasma glucose (if cap blood glucose is high)
- Urine osmolality - high urine osmolality = kidney failing to reabsorb solutes. low urine osmolality = kidney failing to reabsorb water (ADH deficient)
- Electrolytes - primary polydipsia = low serum sodium. In all other pathologies, serum sodium will be high
- Urine, creatinine and eGFR
- Serum calcium - hypercalcaemia is a cause of polyuria
- TFTs - hyperthyroidism causes polyuria
What is diabetes insipidus?
Problem with the ADH pathway means that kidneys don’t concentrate urine and the patient passes lots of urine as a result
What are the different types of diabetes insipidus
- Cranial/central - reduced/absent ADH secretion due to HPG axis defect. Causes are head trauma, pituitary tumours, craniopharyngiomas or metastases, surgery, vascular lesions and meningitis.
- Nephrogenic - kidneys become less sensitive to ADH - so don’t respond to the signals to concentrate urine. Causes include renal damage (low potassium, high Ca, Li, pyelonephritis, hydronephrosis)
How do you distinguish between cranial and nephrogenic diabetes?
Do the water deprivation test
Give desmopressin (ADH analogue) - if cranial diabetes insipidus - the urine will be able to be concentrated. If nephrogenic diabetes insipidus, the urine will still be dilute
In someone with polyuria who has normal plasma glucose and normal urine osmolality, what is the likely diagnosis?
Solute diuresis e.g. due to drugs or contrast agent
