The Irish Blood Transfusion Service has suspended taking blood donations from women who have given blood in the last 18 months, due to an issue with iron-deficiency anaemia.
It has made an appeal to men who donate to help keep the blood supply up.
A problem has been found with a test, introduced in July 2014, used to check haemoglobin levels in potential blood donors.
The test was failing to identify all donors with anaemia, particularly women. Several hundred donors have been affected and contacted.
IBTS medical and scientific director Dr Willie Murphy said that as a result of the issue, some women and a small number of men may have been rendered iron deficient and anaemic from blood donation in the the past 18 months.
The IBTS will now check a blood sample from each donor for haemoglobin. It says there is no issue with the safety of blood transfusions.
But the problem is likely to lead to a fall-off of around 550 unit of blood this week - a quarter of the blood supply.
While this will result in supply constraints, the IBTS expects to meet hospital needs and can import blood if necessary.
As a result, it is appealing to men to donate in the interim.
The blood service will replace the faulty test with an alternative as soon as possible.
It is asking any concerned donors to attend their GP if they are worried that they might be anaemic or iron deficient. The blood service will meet the cost of GP visits and iron checks.
Concerned donors can contact the IBTS at 1850-731-137.
Health Minister Leo Varadkar today said: "I was informed earlier today that the Irish Blood Transfusion Service has identified a problem with the device used by them to measure haemoglobin levels in prospective blood donors.
"I am assured that the IBTS has put in place appropriate precautionary, safety, contingency and communication measures to deal with the issue.
"I am being briefed on the issue on an ongoing basis and will monitor it closely," he said.