Curious to see how we perform a COVID test?

The video shows the laboratory steps involved in testing four patient samples along with one Control. The reagents and procedures are for the “CDC test” for SARS-CoV-2. Still, there is no difference in processing these patient samples from any sample evaluated for respiratory or sexually transmitted infections. The CDC test procedure is very similar to most manual molecular diagnostic tests.

Most infectious disease tests are manual or semi-manual due to their low cost and versatility. These tests, like the CDC’s test, are referred to as Lab Developed Tests or “LDT’s” since many labs have the capabilities of developing tests in house. Large centers with the financial ability, and that exhibit a constant, high volume of samples (to keep expensive equipment busy), will use automated systems, eliminating many of the human interventions and thus potential errors, thereby reducing the frequency of controls used. The end of the video shows the simplicity of a Point of Care (POC) test system and can deliver results in minutes. These have cartridge-based reagents and automated sample processing, but they come at a significant price premium per test, and they only process 1 sample per cartridge.

How does the Control help confirm test reliability?

The Control has a predetermined outcome. All samples, including the Control, will have a “Ct” value reported by the test. The Ct value is an indication of strength (or concentration) of the target pathogen. Labs will establish their clinical thresholds for publishing a ‘positive’ or ‘negative’ result. Ideally, the test system should report a consistent Ct value for Control samples. This method facilitates effective monitoring of the laboratory workflow and ensuring the performance of the tests (and their results) are within the threshold limits. This process is critical in determining whether the patient sample is ‘positive’ or ‘negative.’ If there are significant deviations from the expected result or drifts in the Ct value is detected, the patient sample results may be unreliable, and an investigation will occur.

Results can be affected by incorrect reagents used, improper handling (like poor mixing, etc.), contamination, improper sample placement into the assay plates etc. If any of these happens without the Control in place, it may never know. When the Control results are as expected, there is increased confidence in all results. An investigation determines causation if Control results deviate from expectation, and patient outcomes may be unreliable.

Watch the video as it illustrates how a laboratory conducts the steps involved in testing patient samples.