An in vitro diagnostic (IVD) may demonstrate strong technical performance, but its value can be limited if intended users struggle to operate it correctly. A test that is difficult to handle, contains confusing steps, requires additional equipment, or produces results that are prone to misinterpretation can create barriers to effective use.
This is why usability is a central component of the ASSURED and REASSURED criteria. These frameworks recognise that diagnostic tests must work not only under controlled development conditions, but also in the environments where they will ultimately be used. Robustness, specimen collection, ease of use, result interpretation and time to result all contribute to whether a test can be successfully adopted in practice.
Usability should be considered from the earliest stages of product development rather than being treated as a final checkpoint before launch. Designing for usability begins with clearly defining the intended user and the intended use environment. These factors influence many aspects of test design and should guide development decisions from the outset.
Learning from intended users
Early engagement with representative end users can help identify and eliminate barriers before they become embedded in the product design. Questions such as whether the test is difficult to manipulate, whether there are too many steps, whether instructions are clear, or whether additional materials are needed can reveal important opportunities for improvement. Similarly, assessments should consider whether results are easy to interpret, whether they could be misread, and whether any safety concerns arise during use.
Addressing these issues early allows usability to be designed into the product before design freeze, when changes are generally easier to implement. This approach helps ensure that product requirements reflect the realities of how and where the test will be used.
Verification and validation
By the time an IVD reaches verification and validation, significant usability issues should already have been addressed. However, usability remains an important part of these activities. Developers should evaluate defined usability specifications to confirm that the intended requirements have been met and that users can perform critical tasks consistently and reproducibly under expected conditions of use.
Bridging performance and real-world use
Ultimately, diagnostic performance and usability should not be considered separately. A test may demonstrate excellent sensitivity and specificity under controlled laboratory conditions, but if intended users struggle to perform the test or interpret results correctly, the benefits of that performance may not be fully realised in practice.
Diagnostics are ultimately used by people, not development teams. Even a test with strong laboratory performance may face challenges in real-world settings if users are not comfortable performing the procedure, interpreting the results or incorporating it into routine practice.
High sensitivity and specificity are important measures of diagnostic performance, but they do not, on their own, ensure that a test will be used correctly or adopted successfully. If usability has not been adequately considered, barriers such as complex workflows, difficult specimen collection, confusing instructions or uncertainty in result interpretation can limit the benefits of otherwise well-performing technology.
Embedding usability throughout design, verification and validation helps ensure that a test is practical for its intended setting and user group. It also provides evidence that usability requirements have been achieved consistently. By treating usability as a core design requirement rather than a late-stage exercise, developers can help bridge the gap between laboratory performance and successful real-world implementation.