Several hundred women who donated blood to the Irish Blood Transfusion Service in the last 18 months may have been anaemic when their donations were taken or may have become anaemic as a result of donating, the service has said.
A device used to measure haemoglobin, the element of blood that carries iron, had been giving inaccurate results.
The IBTS has suspended taking blood donations from women who gave blood in the last 18 months, until it has checked a blood sample from each donor.
Women with haemoglobin levels of between 12.6 grams and 16.5 grams per decilitre can donate blood, and levels of 11.5 grams or lower are categorised as anaemia.
The “non-invasive, point-of-care device” was introduced by the IBTS in July 2014 and the test was carried out on donors prior to accepting their donations.
In a statement on Monday evening, the IBTS said it had discovered the device gives inaccurate results in some individuals with anaemia down to, and probably below, 8.4 grams per decilitre.
From last week, the organisation introduced a full blood count on all female donors and of 1,041, 20 donors with anaemia were discovered to have not been detected by the new device. The process is to be extended to all male donors this week.
The organisation's medical and scientific director, Dr William Murphy, said as a result of the issue, several hundred women, and probably a much smaller number of men, could have been rendered iron deficient and anaemic from blood donation in the past 18 months.
He said the device, which uses a white light to measure redness of blood in the finger, missed a subset of women who were anaemic.
Over the next few weeks, the IBTS will introduce new software to reanalyse all the electronic results from all donors who have been tested and accepted for donation since the device was introduced, he said, and any discrepant results will be notified to the donors involved.
“In the meantime we will ask any donors who are concerned or may be feeling a bit under the weather to attend their GP if they are worried that they might be anaemic or iron deficient.”
Dr Murphy said the IBTS will meet the cost of attending the doctor and iron studies.
He has asked that male donors make an extra effort to attend clinics and give blood donations to maintain blood supply until the problems are resolved.
Dr Murphy also said they are confident the issue has not had any impact on blood received by patients.
“We are determined to have this matter resolved as soon as possible,” he said.
Minister for Health Leo Varadkar has said he was informed on Monday that the IBTS had identified a problem.
“I am assured that the IBTS has put in place appropriate precautionary, safety, contingency and communication measures to deal with the issue,” he said.
“I am being briefed on the issue on an ongoing basis and will monitor it closely.”
