7
TABLE 1
Common molecular methods
Tests Polymerase chain reaction ( PCR )
Multiplex PCR
Nanoparticle probe technology Peptide nucleic acid fluorescent in situ hybridisation ( PNA FISH )
Nucleic acid amplification technology ( NAAT )
Methods Labelled probe with two primers to amplify specific target DNA Labelled probe with more than one set of primers for target DNA molecules Nucleic acid extraction with PCR amplification Oligonucleotide fluorescence-labelled probes Hybridisation to species-specific ribosomal RNA Fluorescence detected using a fluorescence microscope Uses specific DNA / RNA target primers Target DNA amplified through PCR / multiplex PCR
inappropriate , putting patients at risk of adverse events and potentially driving the selection of antimicrobial resistance within the wider population . 6 IVDs can provide the prescriber with information to support their decision making during infection management . This can lead to more appropriate prescribing , achieving clinical cure while minimising the harmful consequences of antimicrobial therapy such as toxicity or the development of antimicrobial resistance . The benefits of IVDs must be balanced against their potential limitations if they are used inappropriately , which include over-diagnosis and therefore inappropriate management decisions . 7 , 8
With advancing technologies and increasing numbers and types of IVDs , optimising the value of each diagnostic is critical in preventing overload of information , ensuring cost effectiveness , and delivering the best outcome for patients . In terms of microbiological IVDs , the aim is to shorten the potential window of inappropriate therapy , by providing a rapid diagnosis and descriptions on the in vitro phenotype of an organism . The value of diagnostic testing can be evaluated in several ways , but simply put can be considered as a factor of performance and efficiency . 9 , 10 Performance considers the technical accuracy of the test and its turnaround-time with efficiency considering the utility – cost relationship .
Advances in IVDs for infectious diseases There has been a revolution in IVDs to support the diagnosis and management of infectious diseases in the last two decades . For over a century , traditional laboratory approaches relied on culture-based methods to identify and characterise a pathogen . 11 When culture-based methods were not possible , serological diagnosis was often sought through the detection of antibodies to a specific antigen . In terms of value , these IVDs often had long turnaround-times , from days for culture based-methods to weeks for convalescent serological tests , meaning that decision making was empiric until the results became available .
The development of molecular testing has provided the ability to rapidly reduce the turnaround-time of many microbiological investigations . Common molecular tests are outlined in Table 1 .
Matrix-assisted laser desorption / ionisation – time of flight mass spectrometry ( MALDI-TOF MS ) is a successful example of an IVD for infectious diseases . MALDI-TOF MS works by ionising a prepared sample of bacteria . The ionised material is passed through an analyser that determines the mass-to-charge ratio of fragments , producing a specific spectrum of signals that can be used as a fingerprint to identify the genus and species of organism . 12 MALDI-TOF MS has demonstrated significant value to the microbiology laboratory through its enhanced performance . It significantly reduces turnaround-time for organism identification , taking between 5 and 10 minutes compared with 24 – 48 hours using traditional methods , such as analytical profile index . 12 Furthermore , its high accuracy (> 90 %) and financial saving for the laboratory mean that it satisfies many of the parameters considered as important when determining the value of a diagnostic test . 9 , 10 However , despite these benefits few studies have demonstrated overall patient benefit . 13 This is likely secondary to the need for a better link between the laboratory and clinical teams , current study designs examining heterogenous cohorts and infective organisms , and the remaining reliance on phenotypic bacterial identification using in vitro susceptibility testing .
With increased sensitivity provided by molecular diagnostics , the role of biomarkers specific for bacterial infection that can support the presence of infection versus colonisation / contamination is vital . An example of an IVD with the potential to augment decision making is procalcitonin ( PCT ). PCT is a pro-hormone of calcitonin , an endocrine hormone involved in the regulation of calcium . In a healthy state , PCT is produced at low concentration by the thyroid-C cells . On exposure to bacterial specific >