THE MULTIPLE SLEEP LATENCY TEST - COMPARISON OF SLEEP ONSET CRITERIA

Determining sleep latency is one of the cornerstones of the interpreta tion of the multiple sleep latency test (MSLT). The purpose of this st udy was to compare various criteria used to determine sleep onset. We prospectively analyzed 100 consecutive MSLTs that were performed accor ding to a standardized protocol. We scored each test using three separ ate sets of criteria for sleep onset: 1) one epoch of stage 1 sleep, 2 ) two consecutive epochs of stage 1 sleep, and 3) three consecutive ep ochs of stage 1 sleep. Each method yielded a mean sleep latency and a categorical classification of the record as normal if >10 minutes, mod erate if greater than or equal to 5 and less than or equal to 10 minut es, and severe sleepiness if <5 minutes. The ages of participants rang ed from 4 to 78 years (mean 45.5). The averages of the mean sleep late ncies across all three methods were: 6.2 minutes [standard deviation ( SD) = 4.3] using one epoch, 7.2 minutes (SD = 4.7) using two epochs, a nd 7.5 minutes (SD = 4.9) using three epochs. Using the three categori es of sleepiness, the implementation of the three-epoch criterion vs. the one-epoch criterion produced a change in category in 16 patients ( 16%). Five went from severe to moderate, 10 from moderate to normal, a nd 1 from severe to normal. As compared to using one epoch, using thre e produced an increase in mean sleep latency of at least 50% in 13 pat ients. The use of various criteria for sleep onset, especially criteri a 1 and 3 above, produces differences in interpretation that are neith er rare nor quantitatively negligible. Standardization of the methodol ogy across centers would be desirable in clinical practice as well as for research protocols.