A widely-used pregnancy test is being investigated by Medsafe after reports of false results - but the company that makes it is standing by its product.
The EasyCheck Pregnancy Test Cassette is government-subsidised and is used in hospitals, medical practices and by Family Planning.
Medsafe said in a safety alert it had received several reports from clinicians, district health boards and community providers about either false negatives or technical faults.
The medicine and medical device authority said it was monitoring the reports.
It said it had asked the supplier, Phoenix MedCare, for more information about the device to find out what sort of errors there had been and how many.
But Phoenix MedCare said the product was regularly tested by independent labs and was performing well.
Its managing director, Brad Rodger, said since last July Phoenix had distributed half a million tests and only heard of two potential cases of false negative tests from Medsafe and a handful of inconclusive results.
That was well below acceptable levels for erroneous tests per batch, he said.
But Auckland Women's Health Council wanted the tests recalled immediately, saying any doubt about the quality was too much.
Its spokeswoman, Lynda Williams, said an incorrect result was a huge concern.
"It's denying women time to make choices about whether they continue to drink alcohol, and whether this pregnancy is welcome or not welcome," she said.
"They may be thinking of terminating the pregnancy so there is a need for women to be given reassurance that the testing kits are more reliable than this one seems to be."
Family Planning uses the tests, and said it has had a small number of reports of problems.
Its medical advisor, Christine Roke, said most of those have been about the results being unclear, rather than wrong.
But a false negative result would be a serious problem, she said.
"All tests do have wrong results occasionally so it is important for people to be aware that if they have a result that they don't think is right, then they need to think about whether to repeat the test or seek some help about it," Dr Roke said.
Mr Rodger said it was possible for the tests, which measure hormone levels in urine, to deteriorate or for people to use them wrongly.
"If you're testing later in the day and there has been a lot of fluid intake, for example, that could dilute your urine and if you are very early on in pregnancy, say 10 days or show, it could show a negative result."