April 30 (Reuters) - Humana beat Wall Street estimates for first-quarter profit on Wednesday by a large margin, helped by lower costs and delayed administrative expenses and incremental investments, sending shares of the health insurer up 4.7% in premarket trading.

On an adjusted basis, the company earned a profit of $11.58 per share, above analysts' average estimate of $10.1, according to data compiled by LSEG.

The results were in stark contrast to industry bellwether UnitedHealth. Earlier this month, UnitedHealth missed quarterly estimates for the first time since 2008, in part due to high spending related to its Medicare Advantage plans, sparking a brief selloff in the sector.

Humana is a top provider of U.S. government's Medicare Advantage plans, meant for people aged 65 and older, and those with disabilities.

Investors will be keenly watching for details on the company's medical spending.

The insurer's medical cost ratio - the percentage of premiums spent on medical care - came in at 87.4% for the quarter, in line with its prior estimate. Analysts on average had expected a medical cost ratio of 87.5%.