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. 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 3.

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

GC-MS THCCOOH cutoff, ng/L
20 50 100 200 300 400 500
True positivea   90   75   63   57   54   44   35
True negative   75 155 249 350 375 392 397
Unconfirmed positive     9   24   36   42   45   55   64
False negative 325 245 151   50   25     8     3
Diagnostic sensitivity, %   21.7   23.4   29.4   53.3   68.4   84.6   92.1
Diagnostic specificity, %   89.3   86.6   87.4   89.3   89.3   87.7   86.1
Diagnostic efficiency, %   33.1   46.1   62.5   81.6   86.0   87.4   86.6
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.