Detection times and analytical performance of commercial urine opiate immunoassays following heroin administration

The Federal Workplace Drug Testing Program changed urine screening and confirmation cutoff concentrations for opiate testing from 300 to 2000 ng/mL in 1998. Morphine was the designated target compound. An additional heroin metabolite, 6-acetylmorphine (6-AM), was added to the testing procedure with a cutoff concentration ≥ 10 ng/mL. Testing of 6-AM was required if morphine was positive to assist in medical review. A comparison of the new opiate cutoff concentrations was made with the older cutoff concentration at 300 ng/mL. Six commercial opiate immunoassays, four with a 300-ng/mL cutoff, ONLINE, EMIT, CEDIA and AxSym, and two with 2000-ng/mL cutoffs, ONLINE and EMIT, were selected to test 920 urine samples collected from 11 male human subjects following single doses of heroin. Eight received intravenous doses of 3, 6, and 12 mg heroin HCl and four smoked 3.5-, 5.2-, 10.5-, or 13.9-mg doses of heroin (base). In addition, 183 urine-based blind quality-control specimens were added to the study set to assess linearity, cross-reactivity, and interference. Total morphine, free morphine, and 6-AM were measured in each sample by gas chromatography-mass spectrometry (GC-MS). Linearity, cross-reactivity, and interference results for each immunoassay are described. Detection times, sensitivity, specificity, and efficiency of each assay were determined using data from the specimens collected after heroin administration. Detection times for morphine using the 300-ng/mL cutoff assays was approximately 12 h for low dose and 24 to 48 h for higher doses of heroin. For the two 2000-ng/mL cutoff concentration assays detection time was about 12 h. This was also the detection time for 6-AM by GC-MS. ONLINE had the lowest sensitivity, 60-74%, highest specificity, 98.8-100%, and least interference from a selection of common over-the-counter drugs and opioids. Increasing the cutoff to 2000 ng/mL from 300 ng/mL increased efficiencies of the assays from 72.7 to 82.6% to over 97%.