disorders, psychotic disorders, obsessive-compulsive disorder, and malingering.

The broad term laboratory studies refers to a variety of physiologic tests, imaging techniques, pathology studies, and other means of medical examination that can support the investigation of PTSD as a valid disorder. Laboratory studies are of two general types: reproducible psychologic tests and studies of biologic markers (Robins and Guze 1970). A psychologic test, in this context, measures objectively observed behaviors (patterns of responses to test questions) associated with a disorder. The Minnesota Multiphasic Personality Inventory, for example, can help to distinguish between expression of genuine illness and symptom exaggeration.

A biologic marker (biomarker) is a measurable biologic change that occurs before, during, or as a consequence of a disease process. Many biomarkers are under study, and they support a biologic basis of PTSD (see Chapter). The last 2 decades have witnessed progress in developing laboratory tests to validate PTSD as a disorder but none has been shown to be specific enough to distinguish people who have PTSD from those who do not. In other words, no laboratory test is currently useful for diagnosing PTSD.

Temporal stability is related to whether a disorder retains its distinct profile or evolves into another, established disorder. During the first days and weeks after a traumatic event, an immediate stress response might occur in a large proportion of those exposed. The immediate phase can last for several days or weeks. Thereafter, effects start to decline in most people, depending on the traumatic event and its