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:
â€¢ Osmotic diuresis â€“ diabetes mellitus
â€¢ Loss of antidiuretic hormone (ADH) â€“ cranial diabetes insipidus (head injury, etc)
â€¢ Failure to respond to ADH â€“ nephrogenic diabetes insipidus
â€¢ Excessive intake â€“ psychogenic polydipsia
300-500 mls of urine is needed to excrete adequate amounts of solute each day. Less than this is therefore oliguria.
â€¢ Physiological response to severe dehydration
â€¢ Hypoperfusion of the kidneys â€“ hypotension or damage/occlusion to renal artery/aorta
â€¢ Acute Renal Failure (see Approach to the patient with oliguria)