Mr Rudd was admitted to hospital in Brisbane on Friday and was due to undergo an operation to remove his gall bladder.
He said in a statement he had experienced acute abdominal pain on Thursday and underwent a series of medical tests on Thursday night and Friday morning.
Based on specialist advice, he was admitted to the Mater Private Hospital around 12pm AEST on Friday.
Doctors advised he was likely to be in hospital for a couple of days before being allowed home, while a spokesman said Mr Rudd planned to resume work next week.
But that plan appears to be ambitious according to surgeon and Associate Professor at the University of Sydney Henry Pleass, who recommends at least a fortnight off work after surgery to reduce the risk of infection.
“If the guy is planning to carry on campaigning that would be brave of him,” Dr Pleass told AAP.
“But it is possible – people have had just one day off. It depends on how stoic you are and how desperate for cash.”
Dr Pleass said it was most likely Mr Rudd has a condition called cholecystitis, an inflammation of the gall bladder which causes fever, acute abdominal pain and generally “makes you feel awful”.
It could also be a temporary blockage causing pain for periods of up to an hour known as biliary colic.
Gallstones are most commonly found in overweight women aged in their 40s, and are associated with female hormones.
But Dr Pleass says it also affects one in four men.
He says about one third of the world’s adult population are affected but only about two per cent become ill.
“What makes a person become symptomatic we don’t really know,” he said.
“It’s often associated with poor diet, a western diet with too much fat, (and) being overweight.”
Stress was not thought to be a factor, he said.
The gall bladder stores bile and is emptied every meal time to absorb food.
Problems occur when stones form and calcify over time.
They can grow to 2-3 centimetres but it’s the smaller kind which cause trouble.
“Those are the ones that can go down the bowel and cause jaundice, and all sorts of other nasty complications,” Dr Pleass said.
In the case of cholecystitis, the pain is caused when the gallstones block the gall bladder tract, causing damage to its wall resulting in inflammation and fever.
Most modern surgeons will perform emergency surgery for the condition, a laparoscopy (keyhole) procedure which normally takes less than an hour.
Patients are normally given antibiotics for 24 to 48 hours afterwards and can remain in hospital for a couple of days.
As for Mr Rudd’s recovery?
“He should be fine,” Dr Pleass said. “Probably just a little bit sore.”