Nova Scotia’s health minister is promising a new registry of medical errors for the whole province after a test mix-up led to a woman having an unnecessary mastectomy in Halifax.

Dave Wilson said he hopes to have an interim system in place by the fall and a permanent one in the new year.   He said it's been in the works for a year.

"Medical mistakes are something that does happen in every single jurisdiction around the world. One of the things we need to try and ensure is that we minimize the effects on patients," he said.

The various health districts all track their own mistakes, but the province does not collect the information in one place or analyze the information.

Wilson said he hopes the change will help health care professionals learn from their colleagues' mistakes.

"How do we prevent them? How do you train health care providers better to ensure they don't happen in the future or we minimize the number of adverse effects?" he said.

Capital Health confessed on Monday it made mistakes in two separate instances, both involving cancer patients.

A woman in her 60s had a breast removed when the process was unnecessary and the other patient, who needed surgery, was not scheduled for the procedure until after the mistake was caught.

In a second separate case, tissue samples were switched before the pathology analysis. One patient had an unnecessary diagnostic biopsy and the other patient never got the followup they needed.

Capital Health said there were over 19,000 reports of adverse events in the last fiscal year, but it says only three per cent of cases resulted in harm to a patient. That works out to almost 600 people.

The health minister said he's not aware of any deaths related to medical errors, or other cases of unnecessary surgery.