How accurate are polysomnography exams?

Factors: There are a number of factors that affect the quality of a psg (polysomnogram). It is important to get enough sleep during the study to make a diagnosis (an average of 2-3 hours is usually sufficient). Also it is important to have some "rem" sleep during the study since some sleep events only occur in REM sleep and sleep apnea may be more significant in REM than nrem.

Not perfect: There are no medical tests that are perfect. That means that the are sensitive enough to diagnose everyone with the condition for which the test is being done and they are specific enough to rule out a diagnosis if the test is negative. Having said that there are different types of sleep studies and they are quite good tests and greater than 90% sensitive.