Direct Billing Act - Amends the Public Health Service Act to make it unlawful for any person to present a bill, claim, or demand for payment to any person other than the patient receiving services. Makes it unlawful for any physician to present a bill for ancillary health services to any recipient of such services unless the services were furnished personally by: (1) the referring physician; (2) a physician who is a member of the same group practice as the referring physician; or (3) individuals employed by such physician or group practice who are supervised by such physician or another physician in the group practice. Makes such prohibitions inapplicable with respect to ancillary health services for which payment may be made under title XVIII (Medicare) of the Social Security Act.

Provides exceptions to such prohibitions, including demands for payments made to immediate family members, designated payors of the patient, or a health maintenance organization in which a recipient is enrolled.

Provides sanctions against those collecting payment in violation of this Act. Allows the Secretary of Health and Human Services to suspend, revoke, or limit a laboratory certification as part of such sanctions.

Defines "ancillary health services" as clinical laboratory services, diagnostic x-rays and other diagnostic imaging services and tests, durable medical equipment, and physical therapy services.