Lowering cutoffs for initial and confirmation testing for cocaine and marijuana: large-scale study of effects on the rates of drug-positive results.

A large-scale study was conducted to determine whether lowering the initial testing and confirmation testing cutoffs in urine would significantly affect the positive rates for cocaine (COC) and marijuana (THC). Customary cutoffs for COC are 300 microg/L and 150 microg/L for initial testing (screening) and gas chromatography-mass spectrometry (GC-MS; confirmation), respectively; for THC, the usual respective cutoffs are 50 microg/L and 10 microg/L. By applying a screening cutoff of 100 microg/L for COC and lowering the GC-MS cutoff to 50 microg/L, the COC-positive rate increased from 1.2% to 2.1%. For THC, lowering the screening cutoff to 20 microg/L while leaving the GC-MS cutoff at 10 microg/L increased the THC-positive rate from 2.8% to 4.1%. These increases appear noteworthy.