Health chiefs have admitted that as many as one-in-five throat swab tests for the COVID-19 virus may deliver false negatives.
According to the Irish Independent, the figure could be even higher in circumstances where the tests are not taken from swab sites sufficiently deep in the nasal cavity.
It comes as doctors at several Irish hospitals became concerned when such swab tests either failed to confirm COVID-19 in patients displaying classic viral symptoms, or registered different results from blood tests.
Professor Sam McConkey is head of the department of international health and tropical medicine at the Royal College of Surgeons in Ireland (RCSI).
He told Newstalk Breakfast: "In the early stages of infection - if you're infected today and the next few days - you're negative.
"It takes a while for it to become positive.
"And then also it only lasts positive for about five or six days.
"So even if people are still coughing and still perhaps getting very sick in the latter stages, it can also be negative later on.
"I would still say it's a very valuable test, because if it's negative it really points to you not being infectious.
"So the test we've been using here through March and April has really helped us control the virus really well by detecting cases using that PCR test and tracing all their contacts, keeping everyone in isolation.
"We've actually controlled the virus very well.
"That same strategy has worked in China and worked in New Zealand."
On other tests for those who have symptoms, such as blood tests, Prof McConkey said: "We're evaluating whether blood tests are reliable or not.
"So we're not saying the blood tests that are on the market so far are 100% accurate either.
"So certainly diagnostic tests of ours they do have false positives and false negatives - and even the blood tests we're not finding are 100% reliable."
