Medicare Patient Access to Preventive and Diagnostic Tests Act of 2003

Medicare Patient Access to Preventive and Diagnostic Tests Act of 2003 - Amends title XVIII (Medicare) of the Social Security Act to direct the Secretary of Health and Human Services to: (1) establish procedures for determining the basis for, and amount of, Medicare payment for any clinical diagnostic laboratory test with respect to which a new or substantially revised Health Care Financing Administration Common Procedure Coding System (HCPCS) code is assigned on or after January 1, 2004; (2) set the national fee schedule amounts for tests performed; and (3) establish a mechanism for review of the adequacy of payment amounts for a particular test.

Prohibits the Secretary from: (1) assigning a code for a new clinical diagnostic laboratory test that differs from the code recommended by the American Medical Association Common Procedure Terminology Editorial Panel and results in lower payment than would be made if the Secretary accepted such recommendation solely on the basis that the test is a test that may be performed by a laboratory with a certificate of waiver under the Public Health Service Act; or (2) substituting for the fee schedule amount otherwise established under the Act for a test a least costly alternative fee schedule amount.