The AMA Guides to the Evaluation of Permanent Impairment (Guides) is a well-known standard for quantifying the medical loss associated with an injury or illness. California’s workers’ compensation system uses the fifth edition of the AMA Guides Edition of the American Medical Association (AMA) Guide to the Evaluation of Permanent Impairment. The AMA Guides under the California’s workers’ compensation system is for determining whole person impairment (WPI) and not apportionment under the state’s Labor Code §§ 4663 and 4664.
Labor Code §4663 and related case law construing and applying §§4663 & 4664 define apportionment without reference to the AMA Guides, including any references or examples of apportionment in the Guides. When evaluating the allocation of permanent disability, a physician must provide an evaluation and professional opinion in accordance with Labor Code sections 4663 and 4664. An example from the AMA Guides may be adopted by a physician if he or she provides detailed explanations of how the example addresses the current cause of permanent disability under Labor Code section 4663. Relying solely on AMA Guides is not in common practice in California. The impairment standard is assumed to represent the degree of impairment for a theoretical average worker, i.e., a worker with average occupational demands on all parts of the body and at the average age of 39.