** Health insurer Humana's HUM.N shares rise 6% to $275 premarket

** HUM posts Q1 adj. profit of $11.58 per share, beating analysts' estimates of $10.07 per share, according to data compiled by LSEG

** Co reports Q1 medical loss ratio of about 87.4% vs estimates of 87.5%

** Health insurers expect medical loss ratio -- which is the percentage of premiums it spends on medical care -- to be about 80%

** Co maintains its annual profit forecast of $16.25 per share, slightly below estimates of $16.35 per share

** Sees annual medical loss ratio in a range of 90.1% to 90.5%, compared with analysts' estimates of 90.11%

** As of last close, HUM has risen 2.23% YTD

(Reporting by Siddhi Mahatole)

((siddhi.mahatole@thomsonreuters.com))