Officials have refused to rule out the possibility of the new National Children's Hospital costing more than €2bn.
The total cost of the project stands at around €1.7bn at the moment.
It was initially due to cost just €650m to build.
Secretary General of the Department of Health Jim Breslin was questioned about the rise in costs at the Public Accounts Committee (PAC) earlier by Labour TD and Vice-Chair of the PAC Alan Kelly.
Mr Kelly asked: "Can you guarantee us that this project will come in under €2bn?"
Mr Breslin answered: "So the only variation on the guaranteed maximum price are the exclusions from the contract and we've been asked by the Government to do a scenario of sensitivity analysis on the impact of those.
"That's not complete, but that does include inflation above 4% from July of 2019, so I don't think it takes it into that type of space."
Afterwards, Deputy Kelly said: “It is extremely worrying that the top official in the Department of Health, Mr Jim Breslin, was unable to confirm to me that projected costs for the National Children’s Hospital won’t exceed €2 billion.
"The Department of Health confirmed to me at the Public Accounts Committee that they are now running their projected costs study in parallel with the report being carried out by PWC into what the final cost will be.
“It’s hard to understand why the Government have now commissioned their own internal study, they should just let PWC get on with the job, rather than introduce make-work schemes for the Department of Health, who clearly haven’t handled this project well since the beginning.
“The public don’t believe or trust that the State can produce projects of this scale and judging by some of the facts that became known at today’s PAC meeting, they would be right to feel this way.
“The handling of dealing with these overruns has been absolutely shambolic and the fact that we are still none the wiser as to if the costs will reach the €2 billion mark is embarrassing, especially when we are in the middle of a nursing strike where workers are being told that taxpayers won’t thank them if they get a wage increase. The taxpayers are the ones being taken for a fool when it comes to the cost of this project.”