The use of multiplex nucleic acid assays in diagnostics has become more common and the number of multi-analyte detection methods has increased. Thus the need for EQA for this type of diagnostic assays has become relevant. Multiplex nucleic acid tests are useful in especially respiratory infections where several viruses or bacteria can cause similar symptoms and screening of these pathogens in one assay fasten the turnaround time significantly. Diagnostic tests detecting multiple analytes in one nucleic acid amplification reaction may have decreased sensitivity and/or challenges in specificity, and for this EQA is relevant to ensure proper performance of diagnostic methods.
Several laboratories using nucleic acid testing methods have participated in the traditional antigen detection EQA schemes for influenza A+B and RS virus organized by Labquality. To serve customers using nucleic acid testing methods better, Labquality started in 2017 to offer multiplex minipanel for Influenza A+B and RS virus NAT, where specimen levels have been designed specifically for molecular amplification methods. The round consisted of 5 artificial specimens (1 negative, 2 RSV positive and 2 influenza A virus positive specimens). Specimens were pre-screened using RT-qPCR method.
Results were quite surprising: one RSV positive specimen was challenging, only 51.4% of the participants reported the specimen correctly as positive. Specimen contained an old group A type of strain (Randall). Success rate of the other RSV positive specimen was also low, only 82.9%. Most of the false negative results of these specimens were obtained with the most commonly used method, having RSV detection rate of only 57.5 % (23/40). Results for influenza A virus specimens and for the negative specimen were excellent with only few occasional errors.
These results strengthen the importance of EQA programs for influenza and RS virus multiplex nucleic acid methods to ensure the quality of testing and diagnostics.
2018 EQA program includes several additions for nucleic acid methods especially for multiplexing. Each round has a set of samples containing variable combination or pathogens. The aim of the multiplex EQA scheme is to cover all important pathogens during a calendar year.