Senior health service figures will face MSPs investigating a critical report into falsified NHS waiting times.
Chief executives from Glasgow, Tayside and Forth Valley will answer questions from Holyrood's Public Audit Committee less than a month after ministers were warned that trust in official targets has been put at risk.
An investigation by Audit Scotland, which scrutinises public spending, found problems across the country in the way patient waiting times targets are approached by health boards.
The auditors said their work was hampered by a lack of information and because of inadequately controlled management systems.
The waiting lists problem surfaced in 2011 when NHS Lothian was found to have manipulated waiting time codes, marking patients as unavailable for "social reasons" such as failing to get time off work or being on holiday. Facing extra pressure to meet shorter 18-week guarantees, it was discovered managers were putting pressure on staff to find ways around the system. This included marking patients as unavailable if they refused to travel to England.
Audit Scotland said it had been hard to trace changes on patient records and identify reasons for the use of waiting time codes. They also found that the use of "social unavailability" increased from 11% in 2008 to just over 30% in 2011. The levels then dropped off around the time "fiddled" waiting figures were discovered at NHS Lothian. Internal auditors reported the inappropriate use of unavailability codes at NHS Tayside, on a smaller scale.
At NHS Greater Glasgow and Clyde, auditors said some patients were marked as unavailable for two months. NHS Forth Valley was found to have kept good records in its electronic system but it had the biggest percentage difference between reported and actual waits.
Iain Gray, the convener of Holyrood's Audit Committee, said the report left two "unanswered questions" The former Labour leader said more information was needed about the "inexplicable rise" in the number of patients marked as unavailable for treatment between 2008 and 2011 and the "sudden plummet" in this after the problems at NHS Lothian were uncovered.
Mr Gray told BBC Radio Scotland's Good Morning Scotland programme : "We'll be asking the health boards what their explanation will be." He added: "The other thing I think the committee will want to explore is who knew what when and who did they tell that to. The Auditor General is very clear there were warning signs two or three years ago and really those should have been investigated."
Mr Gray went on: "The committee's confidence in whether these things have been put right will depend very much on the evidence we hear from the boards and indeed from the chief executive of the NHS. Our job as Audit Committee is to follow the audit trail, so we will be asking what happened, why was it there was such a big use of social unavailability and then suddenly a drop in it just at the point when Lothian were found." He also said committee members would be asking NHS chiefs "exactly what they have done to ensure in the future we can have more confidence in the figures".