U.S. laboratory Quest Diagnostics Inc on Thursday raised its full-year forecast for profit and revenue and beat third-quarter estimates, on strong demand for its COVID-19 tests due to the spread of the virulent Delta variant in the United States.

COVID-19 testing volumes in the U.S. had slumped in the first half of this year, but demand rose once again in recent months due to the Delta variant, leading employers and schools to implement strict screening programs.

"We have raised our outlook for the remainder of the year based on higher than anticipated COVID-19 volumes," the company said.

Diagnostic companies like Abbott Laboratories have said demand for COVID-19 tests rebounded during the quarter.

The company raised its full-year revenue forecast to between $10.45 billion and $10.60 billion, from $9.84 billion to $10.09 billion, and full-year profit outlook to $13.50 to $13.90, from $11.65 to $12.35.

Excluding items, Quest earned $3.96 per share, beating analysts' estimates of $2.88.

Net income attributable to the company fell to $505 million, or $4.02 per share, in the quarter ended Sept. 30, from $568 million, or $4.14 per share, a year earlier.

Shares of the company rose 3% before the bell.