The Health Service Executive (HSE) has confirmed it has called in external clinical experts to examine a "very small number" of diagnostic tests in the northeast.
It refused to confirm the nature of the tests under examination, but said they "do not relate to breast services and do no relate to mammograms, ultrasounds, CT scans or MRI scans".
It is believed they relate to X-rays reported on by a locum consultant who worked at a number of hospitals in the region. It is also understood a meeting has taken place to consider the issue after it emerged that one or two lung cancers may have been missed by the doctor, who, it is believed worked for a period at Our Lady of Lourdes Hospital in Drogheda and Our Lady's Hospital in Navan.
The HSE said it is "liaising with external expert clinical input to determine what, if any, impact on patient care arose in this very small number of cases". "The matters referred to in the media relate to a very small number of diagnostic tests," it said.
The HSE said what it called "the exaggerated tone and speculative content of some of this comment" was "regrettable given that it is likely to cause unnecessary anxiety for some patients and their families".
The body said the main concern and the "key learning" from recent events in relation to diagnostic services in the Midland Regional Hospital, Portlaoise, is to "ensure that if there are any concerns regarding any aspects of patient care which are found to be valid the patients and their families will be the first to be informed and supported".
The HSE also said it should be noted that individual diagnostic tests are "not the only means by which a patients need for treatment is identified and dealt with".
"With the benefit of this external clinical input decisions will be made as to the appropriate next steps, if any. This decision making process will be based on the principle of patients and their families being informed and supported as the main priority."
Fine Gael's health spokesman, Dr James Reilly, said patients must not be exposed to a prolonged period of uncertainty.
"The list of places where patients’ confidence in their diagnosis is being undermined continues to grow and the HSE’s response in this case must be considerably different to their response in Portlaoise and elsewhere," he said.
Labour's Jan O'Sullivan said the matter will "add to the growing crisis of confidence in the health service, particularly in regard to procedures for screening and diagnosis of cancer.
"It is now up to the Minister for Health, Mary Harney to take personal charge of the situation and so that the confidence of the public can be won back."