Laboratory and imaging tests have limited use in the assessment of patients with PTSD.
One study found that nearly half (48%) of the patients in general medical practices with PTSD were receiving no mental health treatment at the time they entered the study. The most common reason patients gave for not receiving medication was the failure of physicians to recommend such treatment. 
Cortisol levels may be decreased, norepinephrine and epinephrine levels may be elevated, and hypothalamic-pituitary-adrenal axis activity may be abnormal in patients with PTSD; however, these findings are still only used for research.
Natural opiates, which are produced by the body to mask pain in the face of danger, may be found in higher levels in people with PTSD, even after the danger has passed. This may lead to the blunted emotions seen in persons with this condition.
Magnetic resonance imaging (MRI) studies of the brain suggest that the amount of hippocampal atrophy correlates with the intensity of PTSD symptoms, but MRI is still not a recommended diagnostic test.  Some studies in monozygotic twins show that a small hippocampus may be a predisposing factor to the later development of PTSD in the face of a stressor. 
Although increased arousal is not a required criterion for diagnosis, it might be measurable through studies of autonomic functioning (eg, heart rate monitoring, electromyography, sweat gland activity).
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