Hospital and GP services will be delayed as members of the Medical Laboratory Scientists Association (MLSA) ramp up industrial action in a long-running pay dispute.
The HSE said there will be significant disruption and delays in hospitals from 8am to 8pm today and tomorrow.
It is understood there are up to 14,000 outpatient appointments and 300 to 400 day procedures a day, with a significant number affected.
The medical scientists who want the same pay as clinical biochemists in hospital laboratories will refuse to carry out diagnostic testing of patient samples.
They work in public voluntary hospitals, HSE hospitals, private hospitals and the Irish Blood Transfusion Service.
“This will lead to the cancellation of many inpatient and day-case elective procedures and hospital outpatient appointments across the country,” said the HSE.
It said all routine GP testing services will be suspended on both days and patients currently in hospital requiring tests will also be affected.
The industrial action is expected to lead to delays for patients with non-urgent care needs in emergency departments.
However, services including dialysis and some cancer services will continue.
“While efforts are continuing to try to avert this action, the HSE is working with the MLSA to ensure arrangements are in place on the days for the provision of a limited range of services safely,” the HSE said.
“Appointments and procedures disrupted by the strikes will be rescheduled as soon as possible.”
A spokesperson for the Irish Blood Transfusion Service said blood donation clinics will continue to operate as scheduled, along with testing and processing of all donor blood for hospitals.
Non-urgent patient testing services will be suspended.
Today’s two-day strike follows a one-day stoppage last week. Further strikes are planned next Tuesday to Thursday.
The MLSA said it made every effort to avoid “regrettable” disruption to patients and fellow healthcare workers but has been left with no alternative.
It said the industrial action is being taken in a dispute over unfilled posts, pay parity and career pathway issues.
The union claimed the HSE or Department of Health has made no approach for discussions since last week’s stoppage “despite comments from HSE representatives implying talks were ongoing”.
It said most of its 2,100 members will be on picket lines at all public voluntary and HSE hospitals. Members working at the Irish Blood Transfusion Service will join the pickets for the first time.
MLSA members voted by 98pc in favour of industrial action last November.
Union chairperson Kevin O’Boyle said the HSE and Department of Health are ignoring severe problems and burn out in the sector.
He said medical scientists carry out identical work to clinical biochemists in hospital laboratories but are paid on average 8pc less.
Mr O’Boyle said medical laboratory aides who report to medical scientists start on a higher salary.