(a) The premium rates for a state-approved health benefit plan offered by a health maintenance organization under Section 1501.255 must be established in accordance with formulas or schedules of charges filed with the department.
(b) A health maintenance organization that participates in a purchasing cooperative that provides employees of small employers a choice of health benefit plans may use rating methods in accordance with this subchapter that are used by other small employer health benefit plan issuers participating in the same cooperative, including rating by age and gender, if the health maintenance organization has established:
(1) a separate class of business, as provided by Section 1501.202; and
(2) a separate line of business, as provided under Section 1501.255(b).