And although Dr Paul Bilokopytov was concerned about the possibility of appendicitis, the inquest heard, the general practitioner's clinical opinion was that it could be ruled out.

Luca Raso died in February, 2017, after a week of illness that included vomiting, diarrhea, lethargy, loss of appetite and an instance of vomiting brown liquid, which his mother described as looking like "Coca Cola syrup".

An autopsy found the San Clemente High School student died of peritonitis secondary to a ruptured gangrenous appendicitis.

In the week before his death, Luca's family twice took him to see Dr Bilokopytov at a Bay Medical Group surgery.

On both occasions the doctor said the 13-year-old had viral gastroenteritis.

Luca's mother, Michelle Degenhardt, also called the surgery on two occasions out of concern for her son.

Dr Bilokopytov gave evidence during the second day of the inquest into Luca's death in Newcastle on Tuesday.

The doctor disagreed with evidence given by Ms Degenhardt and Luca's sister, Victoria Raso, on Monday that he had been told the teenager was in abdominal pain.

He also denied the 13-year-old said to him: "it hurts everywhere".

"It is a huge tragedy. If I was suspecting abdominal pain I would have investigated it on Wednesday [during the first consultation]," he said.

"I would never ignore a pain complaint from a young child.

"There was no pain and I ruled out appendicitis, in my clinical opinion."

Dr Bilokopytov also disagreed with evidence from Ms Raso that she told him Luca could not walk unassisted during the second visit to the surgery, three days before his death.

He said there were "no signs of appendicitis" during either consultation - the first taking place five days before Luca died.

Dr Bilokopytov said he was shocked to hear of Luca's death.

"Once you've been burnt, you'll always be more cautious," he said.

"This is not a burn, it's a tragedy and it will stay with me for long."

He disagreed with a suggestion that similarities between the clinical notes from each consultation indicated "auto-queue entries".

The doctor also rejected challenges from the legal representative for Luca's family regarding his method of checking the teenager's pulse, as well as a suggestion that he should have noticed the young man was wearing a pair of pull-up incontinence pants because he was suffering from such severe diarrhea.

Dr James Lynch, a Victorian general practitioner who gave evidence on a panel of medical experts on Tuesday, said it was "inconceivable" that a competent abdominal exam could have been completed without noticing the pull-ups.

He said a patient in Luca's condition should have been treated as having appendicitis until proven otherwise.

"The differential diagnosis is potentially lethal," Dr Lynch said.

Sydney GP Dr Hester Wilson, who was also on the panel, said it was difficult to reconcile between the family's experience and Dr Bilokopytov's records.

She told the inquest that, given what was in the consultation notes, it was "really possible I would have made the same decision".

"It's pretty clear from the doctor's notes that it wasn't an acute abdomen, but at the same time the family is saying he was in pain," Dr Wilson said.

Earlier on Tuesday, the doctor who performed Luca's autopsy told the inquest he estimated gangrene had set-in inside the 13-year-old at least four or five days before his death.

Dr Allan Cala said the condition that claimed Luca's life was bacterial, not viral.

He said he found no evidence that Luca had gastroenteritis in the days before he died and Dr Bilokopytov's clinical notes were incompatible with what was discovered during the autopsy.

But Dr Cala said Luca's condition was uncommon.

"I don't believe most GPs [general practitioners] see people with this kind of condition regularly," he said.

"It's really quite rare."

The inquest, under State Coroner Teresa O'Sullivan, continues on Wednesday.

While you're with us, did you know the Newcastle Herald offers breaking news alerts, daily email newsletters and more? Keep up to date with all the local news - sign up here.