WALTHAM — While it posted record operating profits of $1.4 billion and sales of $12.5 billion last year, Thermo Fisher Scientific Inc. will have to work harder to do better in 2013, its chief executive Marc N. Casper, said Friday.

Casper cited expected slower growth in the US economy and the prospect of automatic federal spending cuts, which would hurt medical research labs that are major Thermo Fisher customers. Given those headwinds, the maker of life sciences tools and specialty diagnostics will have to expand its markets and take business from rivals to continue getting bigger, he said.