This page calculates the models created by Huestis et al. to predict elapsed time since last cannabis use from single plasma cannabinoid concentrations, as described in [Huestis et al., 1992] and [Huestis et al., 2005]. To calculate the models, enter known values in the input fields, and the other fields will fill in automatically. You can also specify the ratios used to convert between blood and plasma concentrations. The default values for these ratios are taken from [Desrosiers et al., 2014].
Model I uses only the THC concentration in plasma, while model II uses the ratio of THCCOOH to THC in plasma. Each model generates a predicted elapsed time along with a 95% confidence interval. The combined 95% confidence interval represents the interval between the smaller lower bound and the larger upper bound of the respective 95% confidence intervals of models I and II. All values shown are rounded to two decimal places (except for the most recent user input which is taken to be exact). Intermediate results are unrounded, even if they are also shown on the page. Thus, for example, if 1 is entered as the THC concentration in blood, 1.47 will be shown as the THC concentration in plasma (using the default ratio). However, the actual THC concentration in plasma used to calculate the models will be 1 divided by 0.68 (approximately 1.470588235).
Created by Cassidy Kelly.