Sensitivity and specificity of cocaine metabolite screening in view of the analytical performance of a fluorescence polarisation immunoassay.
Immunoassays for drug screening are called 'qualitative' or 'semiquantitative' by the manufacturers of these tests and they urgently recommend the user to verify each result exceeding the recommended cut-off value by a confirmation test. For therapeutic drug monitoring assays or for the determination of tumour markers or hormones, similar recommendations are not given, although the same analytical technologies are used for these assays. A scientific validation of the commonly used cut-off values recommended by the official bodies (e.g. NIDA, DoD) is unfortunately not described in the accessible scientific literature. A solution to this problem was sought by evaluating the analytical characteristics of the assay and determining the diagnostic validity of the test using an immunoassay for the cocaine metabolite as an example. Hundred urine samples from people suspected of cocaine abuse and 50 urine samples from patients unlikely to have consumed cocaine were analysed in triplicate with a commercially available fluorescence polarisation immunoassay. From this data we assessed the analytical variance of the assay using the computer program of Sadler & Smith (Clin. Chem. 36 (1990), 1346-1350). Using the functions provided, we calculated the limit of detection (LD) and the lower limit of quantification (LLQ) as well as the so-called power of definition (PD) using a recently published method (Gautschi et al., this journal 31 (1993), 433-440). This procedure is mathematically well defined, uses no artificial standards or calibrators and is in compliance with IFCC recommendations. A clearly defined assessment of the diagnostic performance of an assay is of utmost importance for the discussion of adequate decision levels.(ABSTRACT TRUNCATED AT 250 WORDS)
Hänseler
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Institute of Clinical Chemistry, University Hospital Zürich, Switzerland.
Keller
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H
D003042:Cocaine / Q000031:analogs & derivatives* / Q000652:urine*; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D012680:Sensitivity and Specificity; D015813:Substance Abuse Detection / Q000379:methods*
C005618:benzoylecgonine; D003042:Cocaine