Infection Science – Serological Diagnostics Vocabulary

33 vocabulary flashcards summarising key terms and definitions from the Infection Science lecture on serological diagnostics, covering blood components, unlabelled and labelled immunoassays, ELISA formats, Western blotting, flow cytometry, and clinical applications.

Serology

The study of blood serum components, primarily antibodies, and their reactions with antigens in vitro for diagnosis and research.

Blood Plasma

The clear, yellow fluid portion of blood that contains water, electrolytes, proteins (including coagulation factors and antibodies), glucose, and other solutes.

Serum

Blood plasma that has been depleted of fibrinogen and other clotting factors; the fluid used in serological testing.

Antigen

Any substance that can be recognized by and bind to antibodies, provoking an immune response.

Antibody (Immunoglobulin)

A Y-shaped protein produced by B cells that specifically binds antigens; key classes include IgG, IgM, IgA, IgE, and IgD.

Precipitation Reaction

An unlabelled immunoassay in which soluble antigen and antibody form insoluble lattice complexes that become visible as precipitates.

Agglutination Reaction

An unlabelled immunoassay where antibodies cross-link particulate antigens (cells, beads) creating visible clumps.

Radial Immunodiffusion (RID)

A precipitation assay where antigen diffuses into antibody-containing agar, forming rings whose diameter correlates with antigen concentration.

Hemagglutination (HA)

Agglutination of red blood cells caused by antibodies or viruses, used in ABO blood typing and viral titer assays.

Latex Agglutination

Rapid diagnostic test in which latex beads coated with antigen (or antibody) agglutinate when mixed with complementary antibodies (or antigens) in a sample.

Unlabelled Immunoassay

Serological assay that relies on visible precipitates or clumps without the need for indicator labels (e.g., RID, agglutination).

Labelled Immunoassay

Serological technique that detects antigen–antibody interactions using tagged molecules such as radioisotopes, enzymes, or fluorochromes.

Radioimmunoassay (RIA)

Highly sensitive assay where radiolabelled antigen competes with sample antigen for limited antibody binding sites; signal inversely proportional to analyte concentration.

Enzyme-Linked Immunosorbent Assay (ELISA)

Versatile enzyme-labelled immunoassay for detecting or quantifying antigens or antibodies in liquid samples using colorimetric signal generation.

Direct ELISA

ELISA format in which an antigen immobilised on a plate is detected by a single enzyme-conjugated antibody; rapid but less sensitive.

Indirect ELISA

ELISA that uses an unlabelled primary antibody bound to antigen and an enzyme-conjugated secondary antibody for enhanced sensitivity.

Sandwich (Capture) ELISA

ELISA in which an antigen is captured between two antibodies (capture and detection), allowing sensitive measurement of antigens in complex fluids.

Competitive ELISA

Assay where sample antigen competes with immobilised antigen for limited antibody; higher sample antigen yields lower signal.

Direct Capture ELISA

Format that immobilises purified antigen to capture specific antibodies from a test sample, detected by a conjugated secondary antibody.

Western Blot

Technique combining SDS-PAGE protein separation with antibody probing on membranes to detect specific antigens in complex mixtures.

Flow Cytometry

Fluorescently labelled cell analysis method measuring cell size, granularity, and marker expression on individual cells using laser scatter and fluorescence.

Forward Scatter (FSC)

Flow cytometry parameter proportional to cell size, measured by light scattered in the forward direction.

Side Scatter (SSC)

Flow cytometry parameter reflecting cell granularity or internal complexity, measured from light scattered at 90°.

Precipitin

The visible lattice complex formed when multivalent antigen reacts with bivalent antibody in precipitation assays.

Immunological Memory Test

Serological assessment of existing antibodies indicating prior infection or vaccination, e.g., immunity to measles, mumps, rubella.

IgM

First antibody isotype produced during an acute infection; indicates recent exposure when detected serologically.

IgG

Most abundant serum antibody; presence without IgM often signifies past infection or long-term immunity.

Primary Immunodeficiency Screening

Serological detection of abnormal or absent immunoglobulin patterns suggesting underlying immune system defects.

Automation (in Serology)

Use of robotic platforms (e.g., automated ELISA readers) for high-throughput, fast, and error-minimised serological testing.

Standard Curve

Graph plotting known concentrations versus assay signal, allowing quantitative determination of unknown antigen or antibody levels.

Sensitivity (of an assay)

Ability of a diagnostic test to correctly detect even low concentrations of the target analyte.

Specificity (of an assay)

Ability of a diagnostic test to distinguish the target analyte from non-target substances, minimising false positives.