The state agency created to keep watch over the state’s health care costs has seen its own budget skyrocket by ?160 percent over the past decade in a “very troubling and ironic” trend that has too long gone unchecked, a nonprofit group representing Bay State hospitals charged.

Administrative costs at the Center of Health Information and Analysis have grown to $32 million after spikes of ?21 percent and 6 percent in its appropriations the last two years, according to a letter the Massachusetts Hospital Association sent to CHIA last month.

In this fiscal year alone, hospitals are being asked to pay ?45 percent more than they did in fiscal 2014, not including any “credit” left over from last year, according to the hospital group.

“This trend is unsustainable and directly contradicts the cost growth expectations of the commonwealth’s 2012 health care reform law,” Timothy F. Gens, the executive vice president and general counsel for MHA, wrote in a Nov. 17 letter obtained by the Herald that was sent to CHIA executive director Aron Boros.

“While the agency has the requirement to study cost growth per the law, we find it very troubling and ironic that its own costs — which are billed to the same entities it is charged with measuring — greatly exceed the commonwealth’s benchmark,” Gens wrote.

Andrew Jackmauh, a CHIA spokesman, defended the spikes in the center’s budget, arguing that it took on a range of added responsibilities that its predecessor, the Division of Health Care Finance and Policy, never had and that “increase reflects investments necessary to meet CHIA’s increased obligations.”

Jackmauh also said CHIA didn’t request a budget increase in 2012, its first year under the new law, and that its next budget request is for a 2 percent increase targeted to match inflation.

“We have now moved from a growth mode to maintenance mode,” Jackmauh said.

But in raising the red flag, MHA officials say lawmakers need to step in to change the funding formula, which makes hospitals and ambulatory surgery centers responsible for backing at least one-third of CHIA’s budget.

But as CHIA’s directives have “evolved” under the landmark legislation, Gens said the hospitals’ share has risen to ?50 percent of the center’s administrative costs, straining them as they try to rein in their own costs.

“We don’t propose that they don’t get support,” Gens said of the center. “But what’s turned out in practice since (the law) has been passed, we have a contribution that is not capped and is really not tied to the hospitals and the mission and the services that CHIA provides.”

Not so, said Jackmauh, who argued that CHIA’s range of research — including monitoring overall health care spending growth and analyzing physician groups and others — all still stands to benefit its core funders.

“Hospitals and health plans are among the biggest beneficiaries of CHIA resources,” he said.

The state has leaned on CHIA to closely watch what it’s spending on health care since its creation.