Quest Diagnostics Inc. (NYSE:DGX) will continue to aggressively buy back shares of its own stock in 2010, after its board authorized another $750 million stock repurchasing plan on top of the more than 10 million shares it bought back last year.

The Madison, N.J.-based diagnostics company has been buying back shares since 2008, when it repurchased a little more than $250 million worth of stock, and has been increasing the size of the buybacks ever since. Companies typically utilize stock repurchasing programs to boost shareholder value and because it’s less expensive than paying dividends when firms are flush with cash, a Quest is. The company roughly doubled its cash position during 2009, to $534 million in cash and equivalents, compared with $254 million for the same period last year.

The company has about 183 million shares of stock outstanding, according to a press release.

Quest also reported strong sales for the fourth quarter and 12 months ended Dec. 31, 2009, which helped increase its bottom line by about 25 percent.

Quest grew sales by 2.7 percent during the fourth quarter, to $1.84 billion, compared with just more than $1.8 billion for the same period last year. The increase carried over for the entire year, as Quest boosted sales by 2.8 percent to $7.45 billion, compared to $7.25 billion for 2008.

Company officials said the uptick in sales was a result of increased demand for gene-based and esoteric tests, including cancer diagnostics.

The top-line growth helped fatten its bottom line. Quest reported $729 million in net income for the full year, compared with $581 million during the prior year.

For 2010, the company said it expects sales to grow 3 percent to 4 percent, with earnings per share expected to be between $4.10 and $4.30.