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Differentiation of amphetamine/methamphetamine and other cross-immunoreactive sympathomimetic amines in urine samples by serial dilution testing.
Clin Chem 2006; 52(4):743-6CC

Abstract

BACKGROUND

Immunoassay-based screening for amphetamines has a variable positive predictive value (PPV) for detecting amphetamine abuse. The lack of immunoassay specificity necessitates confirmatory testing by gas chromatography-mass spectrometry (GC/MS), but the technical complexity and expense of GC/MS limit its availability. Physicians may make decisions regarding patient disposition based on unverified results. In this study we assessed the utility of using dose-response properties to distinguish urine samples containing amphetamines from samples containing cross-immunoreactive species.

METHODS

Urine was supplemented with known concentrations of amphetamine, methamphetamine, methylenedioxymethamphetamine (MDMA), or pseudoephedrine. Using a series of dilutions, we determined the maximum change in rate over the fractional change in concentration for each compound in the Emit II amphetamine/methamphetamine immunoassay. Patient urine samples that screened positive for amphetamines were diluted 1:1, 1:10, and 1:20, and maximum slope estimates within the dynamic assay range were determined. An optimal slope cutoff that differentiated samples containing (meth)amphetamine from those containing cross-reacting species was determined by ROC analysis.

RESULTS

The slope of the dose response was largest for amphetamine and methamphetamine, followed by MDMA and pseudoephedrine. The optimum slope cutoff for identifying patient specimens containing (meth)amphetamine was 320 (sensitivity, 96%; specificity, 90%; PPV, 92%). High concentrations of less reactive compounds may mask low concentrations of amphetamines.

CONCLUSIONS

Use of the slope of the dose-response relationship in patient urine specimens can enhance the PPV of presumptive positive immunoassay results but does not exclude the presence of low amphetamine concentrations in samples containing high concentrations of cross-reactive species.

Authors+Show Affiliations

Department of Pediatrics, Washington University School of Medicine, St. Louis, MO 63110, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

16455869

Citation

Woodworth, Alison, et al. "Differentiation of Amphetamine/methamphetamine and Other Cross-immunoreactive Sympathomimetic Amines in Urine Samples By Serial Dilution Testing." Clinical Chemistry, vol. 52, no. 4, 2006, pp. 743-6.
Woodworth A, Saunders AN, Koenig JW, et al. Differentiation of amphetamine/methamphetamine and other cross-immunoreactive sympathomimetic amines in urine samples by serial dilution testing. Clin Chem. 2006;52(4):743-6.
Woodworth, A., Saunders, A. N., Koenig, J. W., Moyer, T. P., Turk, J., & Dietzen, D. J. (2006). Differentiation of amphetamine/methamphetamine and other cross-immunoreactive sympathomimetic amines in urine samples by serial dilution testing. Clinical Chemistry, 52(4), pp. 743-6.
Woodworth A, et al. Differentiation of Amphetamine/methamphetamine and Other Cross-immunoreactive Sympathomimetic Amines in Urine Samples By Serial Dilution Testing. Clin Chem. 2006;52(4):743-6. PubMed PMID: 16455869.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Differentiation of amphetamine/methamphetamine and other cross-immunoreactive sympathomimetic amines in urine samples by serial dilution testing. AU - Woodworth,Alison, AU - Saunders,Al N, AU - Koenig,John W, AU - Moyer,Thomas P, AU - Turk,John, AU - Dietzen,Dennis J, Y1 - 2006/02/02/ PY - 2006/2/4/pubmed PY - 2006/5/4/medline PY - 2006/2/4/entrez SP - 743 EP - 6 JF - Clinical chemistry JO - Clin. Chem. VL - 52 IS - 4 N2 - BACKGROUND: Immunoassay-based screening for amphetamines has a variable positive predictive value (PPV) for detecting amphetamine abuse. The lack of immunoassay specificity necessitates confirmatory testing by gas chromatography-mass spectrometry (GC/MS), but the technical complexity and expense of GC/MS limit its availability. Physicians may make decisions regarding patient disposition based on unverified results. In this study we assessed the utility of using dose-response properties to distinguish urine samples containing amphetamines from samples containing cross-immunoreactive species. METHODS: Urine was supplemented with known concentrations of amphetamine, methamphetamine, methylenedioxymethamphetamine (MDMA), or pseudoephedrine. Using a series of dilutions, we determined the maximum change in rate over the fractional change in concentration for each compound in the Emit II amphetamine/methamphetamine immunoassay. Patient urine samples that screened positive for amphetamines were diluted 1:1, 1:10, and 1:20, and maximum slope estimates within the dynamic assay range were determined. An optimal slope cutoff that differentiated samples containing (meth)amphetamine from those containing cross-reacting species was determined by ROC analysis. RESULTS: The slope of the dose response was largest for amphetamine and methamphetamine, followed by MDMA and pseudoephedrine. The optimum slope cutoff for identifying patient specimens containing (meth)amphetamine was 320 (sensitivity, 96%; specificity, 90%; PPV, 92%). High concentrations of less reactive compounds may mask low concentrations of amphetamines. CONCLUSIONS: Use of the slope of the dose-response relationship in patient urine specimens can enhance the PPV of presumptive positive immunoassay results but does not exclude the presence of low amphetamine concentrations in samples containing high concentrations of cross-reactive species. SN - 0009-9147 UR - https://www.unboundmedicine.com/medline/citation/16455869/Differentiation_of_amphetamine/methamphetamine_and_other_cross_immunoreactive_sympathomimetic_amines_in_urine_samples_by_serial_dilution_testing_ L2 - http://www.clinchem.org/cgi/pmidlookup?view=long&pmid=16455869 DB - PRIME DP - Unbound Medicine ER -