Initial Testing Process (Screening) 

LabCorp conducts urine drug screen analyses according to the Department of Transportation (DOT) testing as specified in 49 CFR Part 40.  Non-regulated samples are processed utilizing similar protocols.  Initial testing of urine specimens is performed using FDA-approved immunoassays.  An assay has been developed for each class of drug.  The antibodies used in the assays have been developed from both monoclonal and polyclonal lines to optimize specificity towards particular compounds.  These reagents have been found extremely reliable for the identification of the presence of the drugs of interest. 

The testing strategy for initial tests begins with validation of the equipment. This process includes performing routine scheduled equipment maintenance followed by instrument calibration using calibration standards of known concentrations. 

Calibration of the instrument(s) is validated using a series of control materials that are fortified with the drug of interest at concentrations above and below the cutoff concentrations.  The calibration of each instrument is applied to each batch of donor specimens. 

Preservation of sample integrity and the incorporation of appropriate open (known to the analyst) and blind (unknown to the analyst) control specimens are of primary importance in initial testing procedures.  All aliquots of original specimens received in the laboratory are under chain-of-custody protocols. 

Each batch of specimens includes up to 47 donor specimens, one blind quality control specimen.  These 48 samples are distributed among 5 ten-space racks.  When the aliquots are received in the Screening laboratory the first and last available positions in the batch are empty.  Prior to the batch being loaded into the analyzer, a positive (125% of cutoff) and negative open control is placed into these two positions, respectively.  In addition, an above cutoff control (125% of cutoff) and a below cutoff control (70% of cutoff) are analyzed at the end of each batch.  The control sequence is for each drug tested.  The result is a batch of 47 donor samples and associated controls (4 open and 1 blind control) -- a quality control challenge of more than the “minimum” 10%. 

This batch of specimens and associated controls includes a custody and control form to indicate the individuals who handled specimen bottles and aliquots (portions of the specimen).  An aliquot custody and control form remains with the aliquots throughout the analysis up to and including disposal. 

The automatic analyzers are connected through a bi-directional interface with the Laboratory Information Management System (LMS).  When the rack of aliquot tubes enters the analyzer, the barcode scanner detects the specimen identification number, and schedules the appropriate test profile, based on the information set up in the account.  Thus, the drug analyses and the specific adulterant/dilution tests, which are ordered, are conducted during the transit of the aliquot tube on the automatic analyzer. 

At the completion of the analysis, results for samples are automatically entered into the LMS database by the analyzer's data management system.  Data review of the analyses is performed utilizing proprietary software on the LMS and requires certain, clearly defined criteria to be satisfied.  A complete list of these criteria is included in the Standard Operating Procedure, which is available for review upon inspection.  Further, the aliquot chain-of-custody and data files are reviewed by an individual trained in data review.  After these reviews, specimens that do not satisfy criteria are flagged and the screening analysis is repeated with appropriate quality control samples.  Upon completion of analysis, a certifying scientist performs the data review and authorizes the release of negative results.

A specimen is deemed presumptive positive if the drug concentration is equal to or greater than the cutoff.  Immunoassays are considered to be semi-quantitative only and should not be used to determine the concentration of drug or drug metabolite present in a specimen.  In addition, because of potential cross-reactivity, all presumptive positives should be confirmed by gas chromatography-mass spectrometry (GC/MS).