Southern Community Laboratories in Dunedin has apologised to the Otago woman who had a mastectomy by mistake earlier this year, SCL pathologist and medical director Dr Peter Fitzgerald says.
The woman's breast biopsy specimen was swapped with another woman's.
"The results for one woman basically ended up being given to the other - that's the reality," Dr Fitzgerald said.
The switch resulted in a false clearance for the other Otago woman.
SCL improved its processes after the error occurred about three months ago to reduce the risk of the highly unusual mistake happening again, he said.
SCL was assisting Southern District Health Board's investigation into the mistake, which would take up to another fortnight to complete.
Dr Fitzgerald said he had felt very "uncomfortable" about the situation and had personally apologised to the woman who had the unnecessary mastectomy.
"I've been practising for not quite 20 years . . . and I've never experienced this before."
He emphasised the "unfortunate" mistake could, theoretically, have been made with any specimen.
The lab had started spacing certain specimens to prevent those of the same type going through at the same time.
It was not practical to space high-volume skin specimens, he said.
Dr Fitzgerald said SCL identified the error soon after it happened, when the lab analysed tissue from the mastectomy as part of usual follow-up procedure.
Finding no pathology which could justify the operation, the lab reviewed specimens from the day in question and discovered the mistake.
"The identification of this problem came from us."
Dr Fitzgerald said the two samples had been taken from the women on the same day, at different times, by Dunedin Hospital radiologists, who correctly identified them and sent them to SCL for testing.
SCL processed the specimens, giving them a unique lab number, and then sent them back to Dunedin Hospital to the SCL-operated lab there.
During the testing process in the hospital lab, the specimens were inadvertently switched when they were each transferred from their original container to another designed for the testing process.
"There's a potential for human error here, and this is what the problem is, I believe.
"As far as I know, it's never happened before [to] us," he said.
As well as the unique lab number, specimens were labelled with patient names, National Health Index numbers, and accession numbers.
The lab worker was still working for SCL.
"Of course they've been spoken to; that goes without saying," he added.
DHB chief medical officer Dick Bunton said the DHB was leading the review into the "patient diagnosis error" that occurred in the SCL lab.
"We regret that the error occurred and have apologised for the harm caused.
The unnecessary operation did not happen at either Dunedin or Southland Hospital, he said.
Mr Bunton said the DHB had "informally" advised the National Screening Unit about the mistake, despite it not being a screening unit issue.
The mistake is separate from issues raised earlier this year about the DHB's BreastScreen HealthCare over what was feared to be an abnormally high number of "false negatives", which could have delayed cancer diagnosis for up to 28 women. However, last month the ministry cleared the DHB, saying the unit had a reasonable rate of false negatives.
When contacted yesterday, Ministry of Health chief medical officer Dr Don Mackie said the women affected by the "terrible mix-up" were not part of the screening programme.
"Our understanding at this stage is that they had symptoms and their doctors referred them for diagnostic investigations and decisions about treatment.
"The investigation will look at all of these steps," Dr Mackie said.
Mercy Hospital chief executive Richard Whitney said Mercy and Dunedin Hospitals had "an interest in an individual that has suffered an event".
"The individual concerned - and we have spoken with the individual concerned - has no interest in any media contact or any issue or story . . . ending up in the media," Mr Whitney said.
"We would respect that for [the] woman concerned and we would ask that perhaps the media respects that as well."
He refused to confirm or deny whether the operation happened at Mercy Hospital.
Southern DHB BreastScreen HealthCare lead surgeon Michael Landmann declined to comment, saying the investigation must take its course.
A spokeswoman for the Health and Disability Commissioner's office yesterday said he was not investigating the issue.
- Additional reporting, Vaughan Elder.
