Sleep studies, or polysomnography (PSG), can be divided into two types: standard, in-laboratory, technician-attended, overnight PSG (gold standard) (Figure 16.4) and portable monitoring (PM) PSG (limited) studies. Standard PSG is indicated in any of the previously described sleep disorders, whereas PM is limited to the evaluation of suspected OSA. A portable, battery-powered sleep-screening device can also be used to identify patients at risk for OSA.