Roeder M, Sievi NA, Bradicich M, et al. - This study was conducted to assess the number of sleep study nights need to to get an accurate diagnosis of obstructive sleep apnea (OSA). Individuals with suspected OSA had undergone up to 14 nights of pulse oximetry (PO) at home, and one night of in-hospital respiratory polygraphy (RP). Researchers examined the accuracy of each of the 13 sleep study nights applying the mean oxygen desaturation index 3% of all 14 nights as a reference. They performed multiple regression analyses to evaluate possible predictors for night-to-night variability. This study included 103 patients who had undergone in-hospital RP. A sensitivity of 71.4% and a specificity of 89.4% for diagnosis of moderate OSA was seen with the first PO night. Using only the first PO night, the negative predictive value was 83.1%, but adding a second night increased sensitivity up to 88.1%. It was reported that OSA may be missed after only a single night of in-hospital RP. Accuracy for diagnosing moderate OSA is increased via multiple study nights, e.g. applying ambulatory oxygen saturation monitoring.