Until now, publicly funded tests were limited to those estimated to have a 20% chance of carrying one of the two BRCA gene mutations, a threshold lowered to 10%.
Awareness of the mutation was raised in 2013 when actress Angelina Jolie opted to have a double mastectomy after testing positive for the BRCA1 gene.
University of Otago genetic researcher Dr Logan Walker, of Christchurch, said relaxing the criteria meant more women would test positive for the mutation, but others would be relieved to find out they did not carry the mutation.
He said mastectomy and ovary removal were effective preventive options, but some people would opt instead for more intensive screening.
Indications for needing a test included women who developed breast cancer in their early 20s.
Up to 500 people a year received the testing now through the public health system, and it was impossible to say by how much this would increase, Dr Walker said.
He said some of his own research concerned ways to improve interpreting genetic testing for better accuracy.
The decision by the publicly funded Genetic Health Service NZ
to relax the criteria has been welcomed by the New Zealand Breast Cancer Foundation.
The old threshold meant New Zealand would lag behind the United Kingdom and Australia, as those countries recently moved to the 10% risk level.
The BRCA mutation greatly increases a woman's risk of breast or ovarian cancer, and was linked to pancreatic and other cancers.
Women with the mutation had a 40% to 90% chance of developing breast cancer.
Breast Cancer Foundation medical advisory committee chairwoman Dr Reena Ramsaroop said the lower threshold "will make genetic testing available to families who have previously missed out, despite being at significant risk of having the BRCA mutation''.
While the move would increase costs, money could be saved in taking the preventive approach, Dr Ramsaroop said.
