Urine volume is a poor guide to renal function as it is physiologically variable and 24-hour collections are often erroneous. However severe oliguria or polyuria imply pathology and require further investigation.
Difficult to set an upper limit of normal, but 4 litres is a lot. Causes:
- Osmotic diuresis – diabetes mellitus
- Loss of antidiuretic hormone (ADH) – cranial diabetes insipidus (head injury, etc)
- Failure to respond to ADH – nephrogenic diabetes insipidus
- Excessive intake – psychogenic polydipsia
300-500 mls of urine is needed to excrete adequate amounts of solute each day. Less than this is therefore oliguria.
- Physiological response to severe dehydration
- Hypoperfusion of the kidneys – hypotension or damage/occlusion to renal artery/aorta
- Acute Renal Failure (see Approach to the patient with oliguria)