Comparison of the enzyme multiplied immunoassay technique and gas chromatography-mass spectrometry for the detection of delta 9-THC-COOH

Youssef H. Gheat

Y.H. Gheat. Medico-Legal Organization, Ministry of Justice, Egypt

We compared enzyme multiplied immunoassay (EMIT) cannabinoid screening results analyzed with the Viva-Twin Drug Testing System with 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) concentrations confirmed by gas chromatography-mass spectrometry (GC/MS).

Urine drug screens are valuable tools in health care, workplace, and criminal justice settings because these immunochemical assays provide rapid, sensitive, and cost-effective results. However, false-positive results of immunoassays can have negative medical or social or legal ramifications. More than 30 metabolites of THC (Δ9-tetrahydrocannabinol) have been identified in human urine. The EMIT cannabinoid immunoassays are calibrated using 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) but cross-react with many urinary marijuana metabolites to maximize the ability to detect cannabis use.

Fifty human urine samples obtained from the forensic medicine institute chemistry laboratory in Cairo, Egypt, were screened by the Syva EMIT d.a.u. urine cannabinoid assay with a cutoff concentration of 50 ng/mL. Specimens were extracted by liquid-liquid extraction and confirmed by GC/MS for the major marijuana urinary metabolite THC-COOH with a limit of quantification of 5 ng/mL. Analytes were identified using an HP-5ms capillary column (30 m×0.25 mm×0.25 µm) and an Agilent 6080n mass selective detector. Splitless injection (1 µL) of the BSTFA derivatized extracts allowed quantification of THC-COOH between 10 ng/mL and 100 ng/mL. Confirmed positive GC/MS concentrations ranged between 25 ng/mL and 100 ng/mL from the 50 specimens analyzed. Immunoassay semiquantitative cannabinoid immunoassay results at 50 ng/mL and GC/MS quantitative results (n=50) at a 5 ng/mL cutoff were used to calculate true-positive, true-negative, false-positive, and false-negative values of 45, 4, 0, and 1, respectively.

When challenged with 50 specimens from the Medico-Legal Organization drug-testing program, the EMIT immunoassay was sensitive (90%). The immunological method is an acceptable screening method for detecting the presence of marijuana metabolites in urine.

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Abstract Region: 
North Africa
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Abstract Category: 
Basic Science