MADRID, Mar 1 (Reuters) - Grifols' $1.8 billion sale of a 20% stake in Shanghai RAAS will go ahead after the due diligence process concluded "with a satisfactory outcome," the Spanish drugmaker said on Friday.

Grifols said the sale to Haier Smart Home, announced in December, will be completed by the end of the first half of this year, provided all regulatory hurdles are cleared.

Grifols, which produces drugs made from blood plasma, had said it would use the proceeds to reduce its debt.

The company has lost about half its stock market valuation since early January, when bearish fund Gotham City Research published a report questioning its accounting and debt levels.

(Report by Inti Landauro; edited in Spanish by José Muñoz)