Linder M W, Valdes R
Department of Pathology, University of Louisville School of Medicine, University of Louisville Hospital, KY 40292.
Clin Chem. 1994 Aug;40(8):1512-6.
The presence of salicylates in urine reduces the signal in Emit assays (Syva), potentially yielding false-negative drugs-of-abuse screening results. We demonstrate that the principal urinary metabolite of salicylate, salicyluric acid (SUA; 2-hydroxybenzoylaminoacetic acid), interferes with the measurement of NADH formed in the assay by reducing the molar absorptivity of NADH at 340 nm. Thus, for a given concentration of d.a.u. analyte the change in absorbance over the assay time interval is less in the presence of SUA. With the Emit cocaine assay on the Hitachi 704 analyzer, the rate of absorbance change (delta AR) monitored at 340 nm for a specimen containing approximately 270 micrograms/L benzoylecgonine (BE) was 57 +/- 1.9 mA/min without SUA and 29 +/- 2.7 mA/min with 5 g/L SUA (n = 20). In contrast, delta AR determined at 376 nm was 18.6 +/- 0.5 mA/min with and 17.9 +/- 0.8 mA/min without 5 g/L SUA (n = 20). Measuring the Emit assay signal at wavelengths where SUA has no absorbance (376 nm) eliminates the interference due to SUA while maintaining the precision of the assay near the cutoff concentration for BE (300 micrograms/L).
尿液中水杨酸盐的存在会降低酶放大免疫测定技术（Syva公司）中的信号，可能会产生药物滥用筛查的假阴性结果。我们证明，水杨酸盐的主要尿液代谢产物水杨尿酸（SUA；2-羟基苯甲酰氨基乙酸）通过降低NADH在340nm处的摩尔吸光系数，干扰了测定中形成的NADH的测量。因此，对于给定浓度的药物分析物，在存在SUA的情况下，测定时间间隔内吸光度的变化较小。在日立704分析仪上进行酶放大免疫测定可卡因时，对于含有约270微克/升苯甲酰芽子碱（BE）的样本，在340nm处监测的吸光度变化率（δAR）在无SUA时为57±1.9mA/min，在有5g/L SUA时为29±2.7mA/min（n = 20）。相比之下，在376nm处测定的δAR在有5g/L SUA时为18.6±0.5mA/min，在无5g/L SUA时为17.9±0.8mA/min（n = 20）。在SUA无吸光度的波长（376nm）处测量酶放大免疫测定信号，可消除由于SUA引起的干扰，同时在BE的临界浓度（300微克/升）附近保持测定的精密度。
