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What are in vitro diagnostics ?

In recent years , advances in molecular diagnostics and specific markers of bacterial infection have provided new methods to support optimised infection management ; they have also presented new challenges . To ensure the true value of in vitro diagnostics is achieved , linkage with antimicrobial and diagnostic stewardship is vital .
Timothy Miles Rawson MBBS DTM & H PGDip MedEd MRCP ( UK ) PhD Imperial College London , Hammersmith Hospital Campus , London , UK
In vitro diagnostics ( IVDs ) play an important role in supporting clinical decision making across healthcare . In vitro is Latin for “ within the glass ” and describes any test that is performed outside of the body . This is opposed to in vivo (“ within the living ”) tests that are performed within the body ( for example , heart rate monitor , thermometer ).
IVDs allow for a large amount of control over conditions , meaning that testing can be performed in a standardised fashion . They also allow for multiple tests to be performed at once and are often reproducible and reliable . IVDs can be performed in many settings , from near-patient tests to centralised laboratories and can be performed on most types of body fluid or tissue .
IVDs often provide important information to support numerous aspects of clinical decision making . These include the screening , diagnosis , monitoring , prognostication , surveillance , and staging of disease . 1 In some cases , they can be used in isolation to confirm a diagnosis . More commonly , IVDs are used to add weight to the clinical history and examination , observed physiological changes , and radiological investigations performed in parallel to such tests .
Types of test Common IVDs employ three key technologies : microbiological tests ( such as bacterial culture ); immunoassays ; and molecular methods ( Figure 1 ).
Microbiology Microbiological methods rely on the ability to grow organisms from biological samples , identify potential pathogens , and determine their susceptibility to antimicrobials in vitro . Culture methods follow standardised protocols within the laboratory and rely on the use of specific culture media . These media can be tailored to select out potential pathogenic organisms from clinical samples through the inclusion or exclusion of certain nutrients and / or antimicrobials . On identification of a pathogenic organism , the in vitro susceptibility of different antimicrobials can be determined through antimicrobial susceptibility testing ( AST ). AST provides an in vitro phenotype of the organism and can help guide targeted antimicrobial treatment in the patient .
Three common methods for AST used in the laboratory are broth dilution , antimicrobial gradient strips , and disc diffusion ( Figure 2 ). These methods have been advanced in recent years by automating many steps involved in the setting up and analysis of tests . For example , inoculation onto plates , detection of growth , determination of zone of inhibition size , and broth dilution susceptibility testing can all be performed on automated systems , enabling reduced time to result and improving lab efficiency .
Immunoassays An immunoassay is a biochemical test that detects the presence or measures the concentration of a molecule in solution . This normally utilises an antibody or antigen that binds with the target molecule . Chemical detection occurs by a range of methods including turbidimetry , chemiluminescence , fluorescence , and electrochemical detection . Common immunoassays include enzyme-linked >
The three key technologies of in vitro diagnostics
Microbiology Microbiology is based on culturing biological samples , identifying microorganisms and measuring their resistance to antibiotics
Immunoassays Immunoassays use an immunological reaction to identify and quantify the presence of antigens and / or antibodies in a sample
Molecular biology Molecular biology is based on the detection of the DNA or RNA genetic sequences that characterise a disease agent in order to detect bacteria , viruses , yeast and parasites