Parameters:
(1) urine 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH) in ng/mL at baseline
(2) urine creatinine in mg/mL at baseline
(3) urine 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH) in ng/mL at followup
(4) urine creatinine in mg/mL at followup
NOTE: The units for urine creatinine are mg/mL, not mg/dL.
ratio of THCCOOH to creatinine at baseline in ng per mg =
= (THCCOOH in ng/mL) / (urine creatinine in mg/mL)
ratio of THCCOOH to creatinine at followup in ng per mg =
= (THCCOOH in ng/mL) / (urine creatinine in mg/mL)
ratio of the followup ratio to baseline ratio =
= (ratio of THCCOOH to creatinine at followup in ng per mg) / (ratio of THCCOOH to creatinine at baseline in ng per mg)
where:
• 24 hour urine samples were collected throughout the study period.
• I could not find mention of random urine samples being collected.
• It appears that the baseline and followup measurements were done on aliquots from the 24 hour urine samples.
• I am assuming that random samples taken 24 hours apart would work.
• Looking at Figure 3 (page 450) it appears that the ng/mg ratio falls by over 50% every 24 hours.
Interpretation:
• A ratio of followup to baseline ratios >= 0.5 was indicative of new use.
Additional notes:
(1) The level of detection (50 ng/mL, 20 ng/mL, 15 ng/mL) will determine how long the THCCOOH can be detected in the occasional user.
(2) At the 20 ng/mL cutoff the occasional user will usually have detectable THCCOOH for 4-8 days.
(3) An increase in the ratio when 2 samples are taken more than 8 days apart is highly suggestive of new drug use.
