Beginning May 1, enrollees in UnitedHealthcare's HMO or HMO-point of service Medicare Advantage plans nationwide must obtain a referral from a primary care provider. This recommendation is necessary before visiting a wide range of specialists. The change limits access to specialty care in these plans. The goal is to adjust the sequence of health care provision. Thus, participants cannot directly visit a specialist without the consent of the primary physician. This move applies to health maintenance in Medicare Advantage programs. The information comes from MedPage Today.