Carole Foot, an intensive care specialist at Queensland's Prince Charles Hospital said by examining a patient's urine could provide information to doctors about whether patients were taking certain medications or were being over-administered, reported ABC science online.
For example, propofol, a common sedative in critical care wards, turns urine pink if given in the right dose but green if patients are getting too much.
Foot has published a paper on what she calls the "uroscopic rainbow" in the Postgraduate Medical Journal. She said the idea for the paper hit her after being on a ward round and discovering a number of patients had discoloured urine.
"Here we were with these highly sophisticated monitoring devices that tell us all sorts of things about our critically ill patients and here we are doing something as old fashioned as looking at urine," Foot said.
"I've seen people worked up about complex problems when they just didn't ask the patient something simple."
In a healthy person, urine ranges in colour from almost clear to bright yellow because of a pigment known as urochrome.
But once the urochrome becomes concentrated, urine can go dark yellow or brownish, which suggests it's time for a drink.
"It's a marker of hydration (which can) be used as a marker of whether you're drinking enough fluid, particularly in summer," Foot said.
Dark brown or tea coloured urine can indicate infection in patients who have undergone heart or valve operations because it suggests the patient is haemolysing, or breaking down red cells.
Urine that turns black when exposed to air can also be a sign of alkaptonuria, a rare enzyme disorder that causes abnormalities of the skin and cartilages. And gout can produce pink urine.
This diagnostic tool goes back many centuries. The ancient Greeks first diagnosed the rare blood disorder porphyria by observing colourful urine and even named the illness after the Greek word for purple.
Then in the Middle Ages, when urine analysis enjoyed its heyday, specimens were routinely examined in a matula, or urine glass, held up to the light.
But urine inspection isn't always fail-proof, said Foot, because individual urine pH levels and genetic factors could influence whether or not certain substances discolour it.