But a recent unexplained plunge has advocates wondering if other forces may be at work.

After four years of growth, Medicaid rolls began leveling off early in 2005, but plummeted this spring. Between April and October, 13,366 Utahns dropped from the government-paid insurance program, representing seven percent of the caseload.

Health officials suspect Utah's hot job market is driving the trend, but admit they can't say for sure. They know who's leaving - mostly parents and children - but not why.

Medicaid eligibility specialist Jacky Stokes is surveying closed cases to determine if applicants are being wrongfully rejected.

"The survey will tell us did the case worker screw up, or the applicant screw up," said Stokes.

But the study could take six months and won't explain what's happening to patients who exit the program.

"Are they getting insurance or just foregoing health care? We don't know. Nobody seems to know," said Patrice Schell, an advocate at Voices for Utah Children.

It's a critical question, considering Utah's ranks of uninsured swelled seven times faster last year than the national rate, said Judi Hilman, executive director of the Utah Health Policy Project.

"Other states are looking for ways to expand Medicaid to cover the uninsured. But here in Utah, a legislative task force is exploring options for cutting Medicaid," said Hilman. "We're a little out of step."

Declining Medicaid enrollment is a national phenomenon, which advocates believe stems from a 4-month-old federal law requiring Medicaid applicants to provide proof of citizenship.

The law aims to guard against illegal immigrants fraudulently obtaining benefits. But advocates fear it's discouraging disabled, elderly and homeless citizens from obtaining health care.

State health department records show missing paperwork contributed to 47 percent of the case closures in July, which saw a record drop in enrollment. Only 5 percent were turned away because they earned too much to qualify for help.

But Stokes doubts the proof-of-citizenship rules are to blame.

She has instructed eligibility workers to extend deadlines for clients who have trouble producing documentation. Also, for all Utah-born citizens, workers can access electronic copies of birth certificates using an inter-agency data sharing tool that other states are looking to emulate.

But that doesn't help the 30 to 40 percent of Medicaid enrollees born elsewhere, said Hilman. "We should be databrokering across states." kstewart@sltrib.com