Excessive Urination
Polyuria is a highly subjective symptom and one which presents rather less often than urinary frequency (which is dealt with separately, see 'Frequency'). Most of the causes of polyuria listed here are also, by implication, causes of polydipsia – the only causes of true polydipsia not included are those due to dehydration.
Differential diagnosis
Common Diagnoses
- Diabetes Mellitus (DM)
- Diuretic Therapy
- Chronic Kidney Disease (CKD)
- Hypercalcaemia (e.g. Osteoporosis Treatment, Multiple Bony Metastases, Hyperparathyroidism)
- Alcohol
Occasional Diagnoses
- Potassium Depletion: Chronic Diarrhoea, Diuretics, Primary Hyperaldosteronism
- Relief of Chronic Urinary Obstruction
- Drugs: Lithium Carbonate, Demeclocycline, Amphotericin, Glibenclamide, Gentamicin
- Cranial Diabetes Insipidus (Hypothalamo-Pituitary Tumour, Skull Trauma, Sarcoidosis or Histiocytosis X)
- Cushing’s Disease from Excessive Corticosteroid Doses and Acth-Secreting Bronchial Carcinoma
- Sickle-Cell Anaemia
- Early Chronic Pyelonephritis
Rare Diagnoses
- Psychogenic Polydipsia (Compulsive Water Drinking)
- Supraventricular Tachycardia
- Didmoad Syndrome (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, Deafness: Autosomal Recessive)
- Familial Cranial Diabetes Insipidus (Autosomal Dominant Inheritance)
- Familial Nephrogenic Diabetes Insipidus (Males only: X-Linked Recessive)
- Fanconi Syndrome
Ready reckoner
Key distinguishing features of the most common diagnoses
| DM | Diuretic Therapy | CRF | Alcohol | High Ca2+ | |
|---|---|---|---|---|---|
| Marked Thirst | Yes | No | No | No | Yes |
| Other Abnormalities on Urinalysis | Possible | No | Possible | No | No |
| Abdominal Pain and Vomiting | Possible | No | No | No | Yes |
| Episodic | No | Possible | No | Yes | No |
| Anorexia/Weight Loss | Yes | No | Possible | No | Possible |
Possible investigations
Likely: Urinalysis, fasting glucose or HbA1c.
Possible: FBC, U&E, serum calcium.
Small Print: Blood film, further specialist investigations (see below).
- Urinalysis: Glucose and possible ketones in diabetes; possible haematuria and proteinuria with renal problems; specific gravity very low in diabetes insipidus and psychogenic polydipsia.
- Fasting glucose or HbA1c: To confirm diabetes mellitus.
- FBC: Normochromic anaemia in CKD; film for sickle-cell anaemia.
- U&E: To detect potassium deficiency and abnormalities suggesting CKD.
- Serum calcium: Elevated in hypercalcaemia.
- Further specialist investigations: Many of the aforementioned causes will need further investigation in secondary care to establish underlying aetiology (e.g. ultrasound and renal biopsy in CKD, water deprivation test for diabetes insipidus, CT scan if possible pituitary lesion, and so on).
Top Tips
- Take time to clarify the symptoms. It is essential to differentiate polyuria from frequency, as the causes are very different.
- Remember alcohol as a possible cause, especially in young males. Patients can be surprisingly slow to make quite obvious connections.
- Refer for more detailed investigation if the symptoms are clear-cut and baseline tests draw a blank.
Red Flags
- Diabetes mellitus is not the only cause of polyuria with thirst. If urinalysis is negative for sugar, consider diabetes insipidus or hypercalcaemia.
- Weight loss and cough in a smoker with polyuria suggests a possible ACTH-secreting tumour. Arrange an urgent CXR.
- If urinalysis reveals glucose and ketones in a known or new diabetic, arrange for urgent assessment with a view to admission for stabilisation.
- Renal disease is likely in patients with polydipsia who have blood and protein on urinalysis.