Tenet Healthcare Corp. has reported a first-quarter loss on costs for labor lawsuits. The net loss was $31 million, compared with a profit of $75 million a year earlier when the company benefited from a $92 million tax gain. Revenue gained 6.9 percent from the year earlier to $2.37 billion. Tenet has tried to gain patients by renovating hospitals to attract doctors and insurance plans, and said admissions increased 1 percent. The admissions increase was helped by a severe flu season and an extra day in the quarter, according to a Tenet statement.