An Otago University dental laboratory says a single mistake several years ago has devastated a patient and its staff.
Health and Disability Commissioner Anthony Hill says a woman was wrongly diagnosed with cancer and underwent unnecessary major surgery after biopsy samples were swapped.
In 2008, the 62-year-old had dental surgery to replace a missing tooth with an implant. She saw an oral surgeon three years later with pain and swelling and a biopsy sample was taken.
The woman's sample was mixed up with another person's during analysis, known as the cut-up process, at Medlab Dental's laboratory.
The mistake was realised after the woman's surgery when there was no cancer present in tissue removed. The other patient got the care he needed soon after following a repeat test.
Medlab Dental was found to have breached patient rights over the case. Mr Hill said human error was to blame, but better processes were needed and the lab has made changes.
The head of the lab, Alison Rich, said she has spoke to the woman many times about what happened. "She couldn't believe how such an error could have happened and it's quite difficult for me to be able to answer that, because I couldn't believe it either."
Associate Professor Rich said the woman has been offered any restoration surgery that might help.
Medlab Dental was following standard procedures, she said, but has tightened these up, with verbal cross-checking, digital bar-coding of samples and quiet time with fewer interruptions.
Associate professor Rich said checking has revealed that there were no other errors made, but admits the sole mistake was terrible.
"We see a number of cases - 2500 to 3000 per year. All the good work we that have done with those cases and wonderful diagnoses that have been made that have helped people gets lost because of one error, which has had devastating results on the patient and for the staff here too."
Medlab Dental has apologised for the mistake but does not know how it happened. Associate Professor Rich aid she and her staff still feel ill about what happened.