The "Hook Effect" (or "hooking effect") is a phenomenon common to bimolecular detection systems involving saturable reagents (beads, labeled antibodies, streptavidin, etc.) used to capture specific binding partners or analytes. The hook effect occurs when an ELISA system is overwhelmed with the target analyte resulting in lower than expected or suppressed readings for high analyte concentration samples – potentially resulting in false negative results. This can be an issue in Forensic Toxicology where Immunoassay techniques are used as the primary screening methodology. It may lead to anomalous or erroneous results especially at high analyte concentrations. It can be resolved by using a second, separate analytical technique (e.g. GC-MS).
In order to evaluate any suspected “hooking” an analyst needs an extraction method with the capacity to handle high concentrations of drugs in realistic settings. In a recent report published in the Journal of Analytical Toxicology (e-published in June 2013), Dr. Sheila Dawling’s team (Department of Pathology, Microbiology, & Immunology; Vanderbilt University Medical Center, Nashville, TN) looked at a presumed hook effect in the semi-quantitative DRI Oxycodone immunoassays in 14 urine samples with gas chromatography/mass spectrometry (GC-MS) >10,000 ng/mL. These samples included the index case, a false-negative result with >75,000 ng/mL oxycodone . Dr. Dawling’s team employed UCT’s flagship Clean Screen DAU sorbent to isolate the drugs from real cases. Her methodology was based on an already validated method (Broussard et al. (Clinical Chemistry, 1997 43, 1029–1032)), which also employed the Clean Screen DAU to analyze codeine, morphine, hydrocodone, and hydromorphone as the trimethyl silyl oximes in urine. Using the premier SPE column available to forensic toxicologists, Dr. Dawling was able to correctly identify and correct this perceived “hook effect” by being able to quantify very high concentrations of the oxycodone in real samples. This report demonstrates why UCT is known for producing the finest SPE sorbents for use with real samples.
In order to evaluate any suspected “hooking” an analyst needs an extraction method with the capacity to handle high concentrations of drugs in realistic settings. In a recent report published in the Journal of Analytical Toxicology (e-published in June 2013), Dr. Sheila Dawling’s team (Department of Pathology, Microbiology, & Immunology; Vanderbilt University Medical Center, Nashville, TN) looked at a presumed hook effect in the semi-quantitative DRI Oxycodone immunoassays in 14 urine samples with gas chromatography/mass spectrometry (GC-MS) >10,000 ng/mL. These samples included the index case, a false-negative result with >75,000 ng/mL oxycodone . Dr. Dawling’s team employed UCT’s flagship Clean Screen DAU sorbent to isolate the drugs from real cases. Her methodology was based on an already validated method (Broussard et al. (Clinical Chemistry, 1997 43, 1029–1032)), which also employed the Clean Screen DAU to analyze codeine, morphine, hydrocodone, and hydromorphone as the trimethyl silyl oximes in urine. Using the premier SPE column available to forensic toxicologists, Dr. Dawling was able to correctly identify and correct this perceived “hook effect” by being able to quantify very high concentrations of the oxycodone in real samples. This report demonstrates why UCT is known for producing the finest SPE sorbents for use with real samples.
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