(Reuters) - UnitedHealth Group Inc Chief Financial Officer John Rex said on Tuesday that the company's 2018 earnings outlook reflects the company's first-quarter business strength and takes into account expectations for medical and flu-related costs.

The company anticipates a 2018 medical cost ratio, or the measure of premiums paid compared to the cost of care, stable at 81.5 percent this year, plus or minus 50 basis points.

(Reporting by Caroline Humer in New York; Editing by Jeffrey Benkoe)