Skip to main content
. Author manuscript; available in PMC: 2011 Aug 23.
Published in final edited form as: Clin Chem. 2010 Apr 1;56(6):1007–1014. doi: 10.1373/clinchem.2009.141754

Table 2.

Immunoassay performance (4 µg/L screening cutoff) in 499 authentic OF specimens at varying Δ9-THC GC-MS confirmation cutoffs.

GC-MS THC cutoff, µg/L
0.5 1 2 3 4 5 6
True positivea   73   65   52   44   32   21   15
True negative 362 389 400 400 400 400 400
Unconfirmed positive   26   34   47   55   67   78   84
False negative   38   11     0     0     0     0     0
Diagnostic sensitivity, %   65.8   85.5 100 100 100 100 100
Diagnostic specificity, %   93.3   92.0   89.5   87.9   85.7   83.7   82.6
Diagnostic efficiency, %   87.2   91.0   90.6   89.0   86.6   84.4   83.2
a

True positive, immunoassay positive and confirmed positive by GC-MS; true negative, immunoassay negative and confirmed negative by GC-MS; unconfirmed positive, immunoassay positive but confirmed negative by GC-MS; false negative, immunoassay negative but confirmed positive by GC-MS.