Calculating dim light melatonin onset in children: A comparison of four estimation methods

Dim light melatonin onset (DLMO) is the gold standard circadian phase marker in humans. Although several methods can be employed to estimate DLMO, no research has compared agreement across methods using data from pediatric populations. Here, we compared salivary DLMO calculated using four different methods, including two fixed thresholds (3 pg/ml and 4 pg/ml) and two individual thresholds (2 SD above baseline and the "hockey stick" method) in data from 49 children (<i>M</i> = 4.40 ± 0.66 y, 57% female). Intraclass correlations among the four methods were all significant (<i>p</i> < 0.001), with the strongest agreement observed between the 3 pg/ml, 4 pg/ml, and hockey stick methods. DLMO values from all methods were positively correlated with sleep timing (<i>p</i> < 0.001). Although the 2 SD method was more discrepant from the other three estimation methods on average, it did yield a more plausible DLMO estimate in one individual identified as a high secretor. Overall, our findings suggest the 3 pg/ml, 4 pg/ml, and hockey stick methods provide reliable estimates of DLMO in young children, whereas the 2 SD method may allow a more accurate DLMO estimation in edge cases of high or low melatonin secretors.