ArcDia International manufactures and markets innovative products for automated rapid testing of infectious diseases. Its development of effective testing capabilities, such as the mariPOC test, is used at the point-of-care setting and enables rapid multianalyte testing with a focus on respiratory illnesses.

Accurate diagnosis and proper treatment of acute respiratory tract infections (RTIs) require in vitro diagnostic (IVD) testing. Optimally, a test result would be available when the patient visits the physician, but this is not usually the case, due to delays in laboratory testing and sample logistics.

To meet this clinical need, IVD manufacturers have focused on the development of easy-to-use, rapid test methods.
A number of new tests have been introduced during recent years. Most of these tests, however, are too cumbersome for nursing personnel to use, and successful operation of the tests requires that lab scientists intervene. Despite a short turnaround time, the sample logistics is a lengthy process, which compromises efficient infection management.

Most of the recently launched tests for RTI diagnostics are based on nucleic acid amplification, either on PCR or isothermal amplification techniques. The potential advantage of PCR is high analytical sensitivity. However, in viral RTI differential diagnostics, the specificity is often even more important than the sensitivity. A false negative viral test result seldom leads to fatal consequences in RTIs. A false positive viral test result, in contrast, may trigger a suboptimal treatment, and can lead to complications by another, undetected disease-causing microorganism.

Despite this, clinical microbiologists tend to favour sensitivity at the cost of specificity. Such preference is certainly justified in some clinical questions, such as in single pathogen screening in blood banks, or in monitoring virus load in HIV therapy. In differential diagnostics of acute RTIs, specificity should not be compromised for the benefit of sensitivity. Recent research data shows that the next generation of antigen detection tests provide specificity of up to ten times more than PCR. Therefore, sensitive antigen testing remains the method of choice for differential diagnostics of acute RTIs.

One of the next generation of antigen detection tests, mariPOC by ArcDia International, is based on groundbreaking laser fluorescence technology. This multi-analyte rapid test is automated and can be operated by nursing personnel in a continuous feed manner. Ease of use enables patients with influenza-like symptoms to be tested by nurses before a doctor’s appointment. In most cases, the results from the test are already available when the doctor meets the patient. Independent clinical studies show that mariPOC provides the highest specificity of all methods in the market. Besides mariPOC, other innovative antigen
detection technologies have been introduced, such as the Simoa technology by Quanterix.

In multiplexed testing, the importance of specificity is highly pronounced, as the rate of false positive findings is increasing. For example, consider a pool of 100 true negative samples that are analysed with a ten-plexed PCR test with analytical specificity of 99% (specificity for single pathogen methods). In this batch of samples, one can expect to get ten false positive results ((1-0.99)×10×100).

This means that the overall clinical specificity is 90%, and every tenth patient would get a false positive diagnosis and treatment. This fact is supported by a number of studies published in highly-ranked scientific journals such as CID, JCM, Pediatrics and PIDJ, which demonstrate that PCR-based detection is often too sensitive.

In addition to being vulnerable to contamination, PCR may reveal analytically true positive, but clinically irrelevant findings, due to DNA/RNAemia. Sufficient test sensitivity is of course important, but in differential diagnostics of acute infections this should not be overvalued at the cost of specificity.

In conclusion, antigen testing and PCR are complementary methodologies – one offers uncompromised specificity, while the other offers extreme sensitivity. None of the methods is optimal for all applications, but the most suited method for each occasion is determined by the clinical question.