A health authority in western Newfoundland is rescheduling appointments and pushing seriously ill patients to the front of the line for cancer and cardiac testing due to a shortage of medical isotopes.

Western Health depends on the Chalk River nuclear reactor for part of its isotope supply. That facility has been shut down for weeks.

Radiologist Ed Mercer said it's difficult to plan ahead, as the shortage means Western Health is receiving a different amount of the material each week.

"We don't know from week to week, from day to day, what we're going to get in … the effect is that the patients are somewhat being jostled around a little bit so they're going to have to be more flexible with their time," said Mercer.

"It's a juggling act by the technologists mainly to decide how we get that done," said Mercer. "We're down some weeks, 20 per cent, 60 per cent. So we're obviously not doing the numbers we were doing before. However, we're tailoring the tests to try and get as much done as possible in the time frame that we have."

Mercer said the situation could get worse, and he is asking people trying to book appointments to be patient.

The indefinite shutdown of the Chalk River reactor in Ontario has cut off up to a third of the world medical isotope supply. Another reactor in the Netherlands plans to shut soon for a month's worth of routine maintenance.