An investigation is under way at the Southern Health Trust after almost 200 people were possibly given an inaccurate Covid test result.
A trust spokesperson told BBC News NI it appears the issue may be linked to one bottle of solution used within the laboratory.
At present 193 people may be affected, which includes inpatients, staff and tests carried out in the community.
It is not clear yet just how many were given a wrong test result.
However, BBC News NI understands that around eight patients were nursed on a Covid ward in Craigavon when in fact they had tested negative for the virus.
Some were given medication to treat Covid, which was not necessary.
According to the trust, the Covid swabs were taken between the 11-16 February this year and the problem is linked to one bottle of solution used in the laboratory.
A statement said the “swabs in question are being reprocessed and the trust is contacting those people affected”.
“All will be offered a retest and we are managing each person’s individual circumstances as required,” it added.
It is not clear whether some patients may have been given a negative result when in fact they were positive.
A deep clean of the laboratory has taken place and a review of procedures is under way.
The trust has apologised for any stress caused and is now working closely with the Public Health Agency on what happened.