From Longman Dictionary of Contemporary Englishsweat bloodsweat bloodWORK HARDto work extremely hard to achieve something Beth sweated blood over that article. → blood
Examples from the Corpus
sweat blood• I could have understood it in Cottee's case if he had been sweating blood for Everton.• Although I remember seeing some one eating chips from a story I'd sweated blood on when I was working in Worcester.• Donald sweated blood to build up his business.• If I had to sweat blood it would be done. 