Under AMA Guides, apportionment is based on?

• A. Medical report of treating physician
• B. Informal rating
• C. Pre-existing disability
• D. Causation

Answer: (D)

Apportionment under the AMA Guides rests on causation—the medical link between the work-related injury and the impairment. Clinicians review history, exams, imaging, and functional findings to determine how much of the impairment is actually caused by the compensable injury versus other factors. If a pre-existing condition contributes, a portion of the impairment can be attributed to that pre-existing condition, with the remainder tied to the work injury, all based on established causation as proven by medical evidence. The basis isn’t simply the treating physician’s report, an informal rating, or the existence of pre-existing disability on its own; it hinges on the causal connection between the injury and the impairment.