An "extraordinary" hospital waiting list audit is under way across Northern Ireland.

Tens of thousands of people are receiving letters as part of a validation exercise to update lists.

The majority of patients will be sent two letters before being removed.

The Royal College of GPs (RCGP) has advised patients to respond to their letters within two weeks to avoid the "significant risk" of losing their place on the list.

Almost 13,000 letters have already been sent as part of the audit, which is in "its very earliest stages".

The Health and Social Care Board (HSCB) has allocated £145,000 of non-recurrent funding to the five health trusts for the evaluation.

Among those already contacted are patients waiting 190 weeks for dermatology and three years for routine ENT appointments.

Nearly 300,000 people in Northern Ireland are on a waiting list for a first appointment with a consultant, according to recent Department of Health figures.

A total of 299,436 patients were waiting at the end of June, which is 23,500 more than the previous year.

More than a third of patients have waited for more than a year - targets state no-one should wait longer than 52 weeks.

Each trust will validate a number of lists.

Dr Grainne Doran, RCGP NI chairwoman, said the number of people receiving letters was "extraordinary because our waiting lists are extraordinarily long".

She said waiting lists validations were generally more common in Northern Ireland than the rest of the UK due to the scale of lists. She encouraged people to reply to the letters.

"There is a significant risk you will lose the appointment if you do not reply as that is how the system works. No action means you will be removed," she said.

'Private treatment'

She said patients may no longer need appointments because they have sought private treatment or their symptoms had cleared up since being placed on the list.

She said the exercise could impact on a GP's workload as the clinical responsibility for patients removed from the list would fall to GPs, who may then have to check patients' notes, going back five years in some cases.

A HSCB spokesperson said trusts were required to routinely undertake waiting list audits to ensure patients still require appointments and that contact details for patients are up to date.

The spokesperson said the validation process would help reduce the number of outpatient appointments lost when patient does not attend or wants to cancel their appointment.