Key terms

• Antigen (Ag): any substance that triggers (generates) the immune system to produce antibodies against it, in immunology an antigen is a molecule/molecular structure present on the outside of a pathogen

• Antibody: aka, immunoglobulin, a protein used by the immune system to identify and neutralise foreign objects e.g. bacteria, virus... recognises unique molecule of the pathogen (the Ag). Neutralising antibody

• Agglutination (Latin, agglutinare, gluing to): the clumping of particles e.g. the process when an antigen is mixed with its corresponding antibody

Diagnosis

Investigations

• General (CBC, creatinine etc), specific (microscopy/culture, serology, molecular)

Interpretation

• Sensitivity, specificity, predictive value, likelihood ratios: see is this test any good?

Reference ranges

• Biological factors: age, sex, diet/nutritional state, time of day, posture, muscular activity, dehydration

• Receiver Operating Characteristic (ROC) curve: discrimination ability

Diagnostic methods

• Microscopy: https://www.ncbionetwork.org/iet/microscope/ (if visible e.g. parasite/protozoa/bacteria)

• Culture:

Nucleic acid detection

• Molecular (≥2 atoms) diagnostics: techniques to analyse biological markers in genome and proteome (proteins expressed by a genome) and how cells express their gene and proteins (DNA[genome]>RNA[transcriptome]>proteins[proteome]>sugars/nucleotides/amino acids/lipids[metabolome]). Application of molecular biology to medical testing.

• Nucleic acid detection test: techniques to detect a particular nucleic acid (DNA and RNA) sequence, and detect/identify a particular species/subspecies of organism. As the amount of a certain genetic material is very small, many nucleic acid tests (NATs) include a step that amplifies the material, terms NAAT e.g. polymerase chain reaction (PCR), Loop-mediated isothermal amplification (LAMP) [not requiring a thermal cycler]

Antigen/antibody detection

• Immunoassay: biochemical test to measures the presence or concentration of a molecule through the use of an antibody (usually) or antigen (sometimes)

• Immunodiagnosis: latex agglutination (LAT), immunofluorescent assays (IFA), enzyme immunoassay (EIA), Western blotting, lateral flow immunoassay (?rapid chromatographic immunoassay)

• Antigen test: detect presence or absence of an antigen (immunoassay of one kind or another). Test kit contains artificial antibodies designed to bind to the Ag e.g. COVID-19, rapid strep test, rapid influenza test, malaria antigen test

• Antibody test: detect IgM or IgG e.g. Enzyme-linked immunosorbent assay (ELISA), rapid chromatographic immunoassay

• Neutralization assay: assess whether sample antibodies prevent viral infection/replication