Urine Adulterant Test for Oxidants Yields Positive Results from Microbial-Contaminated Urine

Growing concern about the wide availability and variety of commercially marketed adulterant products is emerging in the field of forensic urine drug testing (1--4). The active ingredients in these products, which have proven their ability to mask the presence of analytes in urine specimens, include nitrites, glutaraldehyde, chromates, and various oxidants. Drug screeners have several tools at their disposal to help them spot adulterant use through the detection of many of these active ingredients. For example, for several years, a number of commercially available tests have allowed screeners to determine quantitatively the amount of nitrites present in a urine specimen. In addition, the amount of creatinine, pH, and specific gravity are commonly measured to verify the integrity of the specimen. Finally, immunoassays for the detection of chromates and glutaraldehyde have been available for a number of years and have proven to be highly reliable indicators of the addition of adulterants to urine drug specimens. Recently, the adulterant-testing arena gained a new player. The oX PERFECT TM urine test for oxidants (Chimera Research and Chemical, Inc., Asheville, NC) is now commercially available for the purpose of adulterant testing. According to the manufacturer's package insert, "When an oxidizing [agent or agents] is present in a urine sample, it reacts with the oX PERFECT TM reagent containing a substituted benzene compound and forms a color complex, readable on any manual or automated analyzer at a wavelength of 660 nm." We report the results of a small pilot study performed at TriCore Reference Laboratories of Albuquerque, NM. The study was prompted by positive oxidant results for employees who underwent required random drug testing and whose urine samples had been tested with oX PERFECT urine test for oxidants. The positive drug-testing results caught the attention of laboratory staff for two reasons: 1. the results came exclusively from female employees and 2. the transportation times for many of the specimens had been lengthy. (The specimens traveled from their respective collection sites, which included several rural New Mexico towns, to our reference laboratory in Albuquerque, NM.) Moreover, subsequent studies undertaken in response to the positive results indicated considerable bacterial contamination of the samples the women had submitted. The positive urine cultures all grew E. coli in a colony number of > I00,000. Given these facts, we decided to study the possibility of a correlation between positive urine adulterant findings and bacterial contamination of urine specimens with microbial organisms that commonly cause urinary tract infections. The pilot study samples were tested within 12 h of collection with the oX PERFECT urine test for oxidants. We tested 14 random urine samples obtained from asymptomatic volunteer staff who employed "clean catch" sterile collection procedures, were not on medication, and were negative on initial drug and adulterant testing. The urines were all adulterant-negative at the time of collection and did not grow bacterial or fungal organisms on culture at the time of collection. Subsequently, the samples were inoculated with common bacterial urinary tract pathogens including Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Staphylococcus epidermidis, and Pseudomonas aeruginosa. These pathogens were the five most common bacterial isolates of urinary tract infection specimens at TriCore Reference Laboratories in 2003. The pH of the samples averaged ~ 5.5. Table ! demonstrates the results for various adulterant screens after the urine samples in our study were inoculated with 0.5 I~L of common bacterial urinary tract pathogens on days 1 and 3 post-inoculation. (All cutoffs were set to the manufacturers' recommendations.) The results of our small pilot study demonstrated that 6 of the 14 specimens produced a positive oxidant result when monitored over a 3-day period and that microbial contamination of urine can cause a positive oxidant result. Previously, Urry et al. (5) described sources and associated concentrations of nitrite adulteration of workplace urine specimens. The amount of nitrite contamination caused by microbial organisms was shown to be significantly lower than that caused by adulterants containing nitrites. Therefore, quantification allows for differentiation of these two processes. In our experience at our laboratory as well as in our study, we show that microbial contaminants can mimic a positive oxidant adulterant finding. This source of a false-positive test result is not mentioned in the package insert accompanying the