Hospitals and insurers are expected to give their clearest view yet on whether people are having more surgeries and other medical procedures during the next few weeks when they report earnings, according to investors who are closely watching U.S. medical services use.

Investors, who study medical use data as a cue for the right time to buy hospital stocks and sell insurer stocks, say most signs indicate the increase in use is primarily due to a onetime event: the decline in the U.S. of the uninsured population due to the national healthcare reform law.

But, they say, they are on the lookout to see exactly how much that spending has picked up, and if there is a sharp increase in spending per person, which could mean insurers are paying out more claims and that profits will suffer.

A broad economic-based resurgence of demand would represent a shift in the overall health spending trend, which has been dampened by years of economic downturn and an increase in the percentage that consumers spend out of pocket.

"Our expectations are not for an economic-driven increase in utilization," said Joel Emery, a co-portfolio manager at Fred Alger Management, describing the current health utilization trend as moving from a decline to a break-even or slight positive. "It's just the magnitude of how big it's going to be in terms of the Medicaid and (health) exchange expansion."

An estimated 10 million people have gained insurance coverage this year through the expansion of Medicaid and the introduction of subsidized private health plans under the Affordable Care Act, often called Obamacare.

That has poured more people into a system that contracted during the economic downturn as people lost their employer-based insurance plans or cut back on spending on elective healthcare.

About three months ago, hospital stocks rose - and insurers fell - after LifePoint Hospitals Inc reported that it was seeing an uptick in demand due to the economy. Some hospitals backed that notion, while others said it was only Obamacare affecting volume. Insurers said they had yet to see any change in per person spending, and attributed some higher spending to costs for a new drug to treat Hepatatis C.

Hospitals are experiencing an increase in volume in some areas, such as patients who have hip and knee procedures that they had put off when the economy was at its weakest, according to David Heupel, a healthcare analyst for Thrivent Asset Management. Johnson & Johnson confirmed earlier this week that they had seen two consecutive quarters of increases in these procedures, he pointed out.

Based on tracking of prescription volumes, hospital visits and physician visits, there has been just a small increase in medical services use, he said.

Jeff Jonas, a portfolio manager with Gabelli & Co., said he believes the insurers have not been caught by a sudden surge in increasing demand. UnitedHealth Group Inc will kick off earnings on Thursday morning and LifePoint is the first hospital scheduled to report, on Friday.

"It has been a modest acceleration this year and it's still well within what they've (the insurers) priced for and what they've expected for cost growth," Jonas said.