Anthem Blue Cross customers got a shock this week when the health insurer informed thousands of individual policyholders that their premium rates will jump as much as 39 percent on March 1.

"There aren't any other parts of our society where people have no regard for inflation rate and increase their prices this much. I can't imagine anything in the world that's going up 39 percent," said Josh Libresco, 54, of San Rafael, as he grappled with the news that his family premium will go from $858 per month to $1,192 - and that's with a $5,000 deductible.

Anthem, which has reportedly sent letters this week to those who buy their coverage individually and are not covered by a group policy, said rising health care costs led to the increase.

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The company, based in Woodland Hills (Los Angles County), declined to say how many customers received the increase or what the average premium hike was, but the insurer has the largest number of individual customers in the state. Last year, when Anthem Blue Cross raised rates by as much as 68 percent for some customers, the company said it had about 800,000 members.

The Department of Insurance plans to hire an actuarial firm to look into Anthem's "alarming" rate increases, said Darrel Ng, spokesman for the department.

Unlike home and automobile insurers, California insurers can legally raise rates for policyholders as much as and whenever they want. Regulators technically oversee the increases, but they have no power to control rates.

The most recent effort to require state regulators to approve health insurance rate increases, a bill by Assemblyman Dave Jones, D-Sacramento, failed to pass the Assembly Health Committee in April.

For Jeff Sher of San Francisco, who is both an independent health insurance agent and an Anthem customer, his 38 percent increase comes on top of a 41 percent increase last year. That means that in just a year, his premium increased from $273 to $530 per month, or 94 percent.

Sher, who is 59, said he hasn't needed to see a doctor in seven or eight years.

"It's all based on this illusion there is a free market in this product. But you can't shop for health care, particularly after you're already sick," he said. "You can't shop for a carrier because there is almost no competition."