Accurate pulmonary impairment ratings depend on a valid and reliable lung function test and appropriate application of the criteria provided in the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition. The two lung function tests are dynamic and static; the principal dynamic test is the cardiopulmonary stress test [see sidebar, “Cardiopulmonary Exercise Testing,” in this issue of The Guides Newsletter]. To rate pulmonary impairment using Chapter 5 of the AMA Guides, Sixth Edition, a physician should obtain the spirometric results and the value for the diffusion of carbon monoxide across the alveolar capillary membrane of the lung (DLCO); the latter should be administered according to American Thoracic Society criteria. A six-minute walk test is a standard test of pulmonary reserve in lung disease patients and may be part of the individual's physical examination. Each diagnosis table in Chapter 5 is divided into variables or factors that determine the impairment rating. Each impairment class (except 0) has five grades (A through E). Once the evaluator uses objective test results to assign the impairment class, the non-key factors are considered to determine whether the impairment should be adjusted from the default value. To determine the adjustment, the evaluator subtracts the impairment class integer from each non-key factor integer, and the differences are summated for the net adjustment.