A drop in the number of blood donations has had a severe impact of supply levels, prompting a new appeal for donors.

The Irish Blood Transfusion Service (IBTS) expects current supplies of the main blood types to last just three more days.

It is calling for an extra 1,500 donations over the next three weeks to ensure it can keep up with demand from hospital.

Stephen Cousins, IBTS donor services manager, told Newstalk.com that the service aims to hold around seven days of supply at any given time.

But recent weeks have seen a significant decline in donations of the two most common blood types, O positive and A positive, he said.

The so-called universal type, A positive, which can be used in emergencies when a person’s blood type is not known, is also in short supply.

"In summer, it’s difficult to keep donations going. It takes a lot of work," Mr Cousins said.

"People’s routines are different - they may be travelling, for example."

Attendance at clinics has fallen to 6% on some recent weeks, he said.

Unless there is a significant increase in donations, he said, supply to hospitals may be threatened.

The IBTS is holding extra clinics this Sunday in Wexford Town, Celbridge and Mountbellew. Details are available on www.giveblood.ie