Feb 9 (Reuters) - U.S.-German genetic testing company Qiagen reported better-than-expected quarterly earnings on Tuesday, citing very strong demand for COVID-19 testing combined with improvements in non-COVID-19 areas of its portfolio.

Qiagen's products include several types of ultra-rapid, portable and antigen-based coronavirus tests that have boosted its shares by around 30% since the beginning of the pandemic, but it expects sales to keep growing even after a mass rollout of COVID-19 vaccines.

"Teams are working on regulatory submissions and expanding the use of key solutions in our COVID-19 portfolio that also have applications once the pandemic has subsided," Chief Executive Thierry Bernard said.

At the same time, the company is still working on ramping up production capacity for core COVID-19 products and ensuring they accurately detect new variants of the virus, Bernard said, adding Qiagen sees improvements in non-coronavirus products as well.

As improved demand trends for Qiagen's QuantiFERON tuberculosis test, cancer diagnostics and DNA sample technologies complemented coronavirus-related sales, fourth-quarter net sales rose 36% to $571.2 million on a currency-adjusted basis, beating the $539.14 million expected on average by analysts in a Vara Research poll.

For the first quarter of 2021, Qizgen expects net sales to grow at least 45% at constant currencies, while adjusted earnings per share (EPS) should be between $0.60 and $0.62 compared to $0.34 a year earlier.

The company also confirmed its guidance for 2021 adjusted EPS and net sales growth.

Late on Monday, Bloomberg News reported that U.S. diagnostics firm Quidel Corp is looking to make a takeover offer for Qiagen, a move that would follow Thermo Fisher's bid from August 2020 that was rejected by shareholders as being underpriced. (Reporting by Zuzanna Szymanska in Gdansk Editing by Chris Reese and Cynthia Osterman)