[co-author: Vicky Vlontzou]
On 15 April 2020 the European Commission issued guidelines regarding COVID-19 in vitro diagnostic tests. The guidelines offer an overview of the different types of test and their purposes as well as the relevant EU regulatory framework. They also include considerations regarding test performance as well as the validation of that performance and provide elements that the EU Member States and stakeholders must take into consideration when defining national strategies.
The guidelines provide that the relevant regulatory framework for COVID-19 related in vitro diagnostic tests is the Directive on in vitro diagnostic medical devices 98/79/EC.
Overview of tests and their purposes
According to the guidelines COVID-19 tests can be grouped by scientific rationale, type of technology, intended user, and location of testing.
In terms of scientific rationale, the tests fall broadly into two categories: a) those detecting the SARS-CoV-2 virus and b) those detecting past exposure to the virus, known as antibody tests.
The first category is divided into two sub-types:
- Tests detecting the genetic material of the virus by transverse polymerase chain reaction (RT-PCR);
- Test detecting components of the virus, known as antigen tests.
In terms of type of technology commercial CE-marked tests can be either rapid, which involve non-automated procedures and are designed to give a fast result, or automated for use on analyzer machines (non-rapid tests).
As regards their intended user, tests can be designed to be used by health professionals or by lay users (self-tests).
In terms of location of testing, they can be either laboratory-based or near-patient tests, performed outside laboratory facilities.
Considerations on test performance
specificity, diagnostic specificity, accuracy, repeatability, reproducibility, including control of known relevant interference and limits of detection stated by the manufacturer.
Manufacturers should explain their choices of performance levels in the instructions for use and determine the specific purpose in accordance with the choices made.
Furthermore, the guidelines outline the drawbacks and limitations of test performance that should be taken into account in the context of population testing. For example, insufficient diagnostic sensitivity can lead to missing infected individuals, while insufficient diagnostic specificity can lead to imposing confinement measures on individuals who are not true positives. This is why sensitivity must be prioritized at the control stage of the disease, while specificity is more important at the de-escalation stage.
Another limitation that must be taken into account by EU Member States and stakeholders is the continuous mutations of the virus, which may render particular RT-PCR tests ineffective. This is why the mutation profile of the virus must be monitored.
Validation of test performance
The performance of the device may vary in practice compared to the performance study the manufacturer has conducted for the purposes of CE-marking due to the rapid development of the pandemic. This is why the guidelines recommend that manufacturers conduct additional validation of the clinical performance of commercial COVID-19 tests. This can be achieved by comparison with a reference method in a sufficiently large number of target population subjects. In this context, it is highly recommended that scientific peer-reviewed results be taken into account.