Selection and Troubleshooting of Immunoassays

The most common assays used in workplace drug testing regimes include homogenous assays which are used with different automatic analyzers. Therefore, one single instrument would never meet the requirements of all the laboratories and that is why, dealers offer variety of shapes and sizes in the instrument kits. A laboratory should therefore, identify its goals and objectives so that it can accomplish those using appropriate testing systems. This template can then be utilized to evaluate different options while considering instruments and reagents. Even though, the importance of different factors varies according to different laboratories, some important points to consider are as follows:

  • The environment of the laboratory including the labor, space and the compatibility of different systems and the LIS – laboratory information system interface
  • The present and predicted sample volumes, thereby allowing enough capacity for growth
  • The speed of analyzer – i.e. the reportable test quantity per hour along with sample throughput
  • The capacity of test analyzer – i.e. the quantity of reagent slows available
  • Validated instruments available for selected assay reagents
  • The costs, such as capital equipment, service agreements, time, requirements for reagent volume and labor
  • Referral to other laboratories for further consultation
  • The advantages and disadvantages of utilizing single or many dealers for supplying instruments and reagents

All analytical systems require regular monitoring of assays and their performance so that accurate results are ensured. For assays, monitoring is done by open Quality control specimens, below and above the cutoff ranges. When systems don’t meet the acceptable criteria, trouble shooting is done to find out the basic cause of failure. Therefore, at times, it is not appropriate to separate the reagent from the analyzer in order to find out where the fault is, and it can be a combination of both the reagent and the instrument.

So, routine preventive and daily maintenances are done along with operational checks so that the mechanical as well as the performance operations of the instrument can be verified. Enthusiastic performance as well as the documentation of these tasks minimize the time and provide real time instrument conditions to be used in the troubleshooting procedures. Recording of lot numbers for reagents, quality control material and calibrators with their daily calibration can ensure quality control results.

Some considerations while troubleshooting assay’s performance are given below:

Quality Control

The most frequent problem associated is the lack of quality control material to fulfill the acceptability criteria. This can occur as an individual occurrence or can be due to a bias developed over some time. Random failures can likely result due to deterioration or insufficient volume of quality material in the sample, which is resolved by replacing the material. An ongoing bias or shift indicates systematic issue. Though, minor change in the quality control can be due to improper preparation, storage or shipping of the reagent. The manufacturer can provide information related to in-house reagent testing and reports from other alternate users for comparison. The development of quality control bias over a lot of time can be due to the deterioration of quality control reagents or materials or may indicate problems with the storage parts that require temperature control or refrigeration. Mechanisms such as reagent dispensing and pipetting of instruments along with technological errors like improper placement of quality control material should be given consideration.

Other Considerations For Reagents

Monoclonal antibodies used for drug abuse testing have enhanced the consistency of reagents. However, even changes occur in these systems over a period of time and the antibodies shift their affinity and reagents alter their formulations which can gravely impact the performance of immunoassays. The monitoring of calibration, quality control and reaction curves can provide insight about the shifts in reagents. Even though, minute changes don’t impact the results’ accuracy, the change in the affinity of the antibody and its specificity over time can cause poor recovery and assay performance.

Proficiency Test Performance

Programs related to the external proficiency testing (PT) can give the laboratory an independent evaluation of the performance of the assay along with its comparison to different reagent systems and other users. PT performance is important to monitor as it is an essential part of the quality assurance program at laboratories. The errors or biases which occur can indicate unidentified problems that surpass monitoring systems. These screening errors can indicate bias or error in calibration or identify cross reaction or integrity problems. PT sample matrices or analyte’s composition can even lead to problems in performance. For instance, PT samples which are prepared using d,l-amphetamine might not give the same performance as those which are made with d-amphetamines. Therefore, the laboratories should go through the results of these events with great caution, while performing a base cause analysis to detect errors and take proper actions accordingly.

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