It is a routine practice for all workplace drugs-of-abuse testing programs to use the immunoassay as an initial testing methodology. Therefore, this initial assay is used to spot and separate donor samples that are negative and those that are presumptive positive/non negative. The negative ones are deemed negative where as the non negatives are sent for further testing and confirmation. In the US statistics, more than 90% of samples are deemed negative which are reported in the initial assay result. Commercial kits are also available which can be used with automated instruments and kits that can make this technology ideal for use in laboratories. These reagent kits are formulated in order to recognize analytes within specific drug classes that can determine thresholds of substance use and abuse according to the regulations set by standards such as SAMSHA, CELIA and CAP. The drugs and their respective cutoffs are listed in Tables 2.3 and 2.4 below.
In workplace drug testing programs in the US, standard sample is considered as urine. However, alternate samples such as oral fluid, sweat and hair have also been used lately. Even though the Federal Workplace Drug Testing Guidelines only allow the use of urine as an ideal sample, non regulated programs adhere to using other samples as well. There are many commercially available assay kits which are highly specified according to different uses for specific sample types. These kits consider different thresholds and sensitivity that is needed to detect varying drugs/metabolites in different samples. Even though, urine sample doesn’t need to be manipulated before it is tested, some non-urine samples need to be prepared prior to testing.
Volume Of Specimen
For an assay test, comparatively small sample volume is needed as the total volume would include the nominal value for every test i.e. lesser than 20 µL along with the deal volume needed for instrument vessel. Normally, 1.0 to 2.0 mL aliquots are poured for initial testing procedures.
Generally, qualitative and semi-quantitative formats are available for the immunoassay tests related to workplace drug testing regimes. However, the type of method that is chosen depends on the laboratory preference, type of client, program designing and its compatibility with other systems such as LIS (laboratory Information System) interface and other analyzers.
Qualitative testing systems have single point calibration technique which is defined at a fixed cutoff range established to build threshold. The results of the analyzed samples are compared with cutoff calibrators. Those having response more than or equal to the cutoffs are taken as non negatives where as those having response lesser than the cutoff range are taken as negatives. The requirement of the quality control to screen applications is also qualitative. This application is quite straightforward and gives information to separate non negative and negative samples which are used in a lot of large volume laboratories in the US.
Semi quantitative assays use multiple point calibrations and the results are depicted according the curve, having a numeric result which estimates the drug’s concentration. The quality control requirements for these systems are also quantitative. Theoretically, semi quantitative results give better comparable results to assess initial test with the confirmatory test and also predict if the samples need to be diluted before confirmatory tests are revealed. Even though, it’s useful as far as assays having dominant compound such as cocaine metabolite Benzoylecgonine is concerned, it is complexed by have multiple drug cross reactions within the sample class of drug for many assays. As Figure 2.9 shows, a variety of GC/MS results of morphine can be known for the same initial test results which are expressed as absorbance units. This is so because, in this particular case, many opoid related compounds such as morphine, codeine, hydrocodone and hydromorphone react with immunoassay for opiates in the urine sample, thereby resulting in a less useful result to estimate the actual concentration of drug in the sample.