Diagnostic Immunology Services – Immunochemistry & Related Testing

Vocabulary flashcards summarising key terms, methods, analytes, and clinical applications mentioned in the Diagnostic Immunology Services lecture.

Regional Immunology Laboratory (Belfast)

Northern Ireland reference lab serving ~1.82 million people and processing ~160 000 samples and >540 000 immunology tests per year.

Immunochemistry/Proteins Section

Laboratory area measuring serum IgG, IgA, IgM, IgG subclasses, functional antibodies, C3, C4, rheumatoid factor, cryoglobulins, and CSF oligoclonal bands.

Nephelometry

Analytical technique in which light scattered by antigen–antibody complexes is measured; scatter is proportional to complex concentration.

Turbidimetry

Technique that records the reduction in light transmitted through a suspension of immune complexes; inverse relationship with complex quantity.

Antigen Excess Testing

Analyzer step adding extra antibody to ensure large-analyte samples fully react, preventing falsely low nephelometric/turbidimetric results.

Roche Cobas Modular System

Automated platform used for quantitative IgG, IgA, IgM, C3, C4, and rheumatoid factor assays.

Helena Nexus / SAS

Systems performing serum protein electrophoresis, immunofixation electrophoresis, immunotyping, and CSF oligoclonal band analysis.

Binding Site SPA Plus

Specialised analyser for quantifying IgG subclasses (IgG1–IgG3 in Belfast; IgG4 referred to Sheffield).

Rheumatoid Factor (RF)

Predominantly IgM autoantibody against IgG-Fc; elevated in RA, SLE, infections, autoimmune liver disease, and can be part of cryoglobulins.

Anti-Cyclic Citrullinated Peptide Antibody (CCP)

Highly specific autoantibody used with clinical findings to diagnose and predict rheumatoid arthritis progression.

Complement C3

Central complement component; rises in acute phase response, falls in chronic inflammation, SLE, partial lipodystrophy, and MPGN.

Complement C4

Classical/lectin pathway protein; decreased in SLE, angioedema, cryoglobulinaemia, and during chronic inflammation.

CH100 (Classical Pathway Haemolytic Complement)

RID assay measuring total functional activity of the classical complement pathway by 100 % lysis of sensitised sheep RBCs.

AH100 (Alternative Pathway Haemolytic Complement)

RID assay determining alternative pathway function using sensitised chicken RBCs; 100 % lysis denotes normal activity.

C1 Esterase Inhibitor (C1INH)

Regulatory protein measured for quantity/function; deficiency leads to hereditary or acquired angioedema.

Radial Immunodiffusion (RID)

Gel diffusion method where antigen diffuses into antibody-containing agar to form measurable precipitation rings.

Membrane Attack Complex (MAC)

C5b–C9 complex that inserts into pathogen membranes; absent if terminal complement components are deficient.

Serum Immunoglobulin Reference Ranges (Adult)

IgG 6.0–16.0 g/L, IgA 0.8–2.8 g/L, IgM 0.5–2.0 g/L (quantified by nephelometry).

Paraprotein (Monoclonal Protein)

Abnormal immunoglobulin produced by clonal B-cells or plasma cells, detected by electrophoresis; key in multiple myeloma work-up.

Selective IgA Deficiency

Most common primary antibody deficiency (~1 : 400); low/absent IgA with normal IgG and IgM; may be asymptomatic or cause infections.

Hyper-IgM Syndrome

Immunodeficiency characterised by high/normal IgM with low IgG and IgA due to class-switch defects, leading to recurrent infections.

IgG Subclasses

Four forms (IgG1, IgG2, IgG3, IgG4) differing in hinge structure and function; deficiency may cause recurrent respiratory infection.

IgG2 Deficiency

Most frequent subclass deficiency; often paired with IgG4 deficiency and linked to recurrent chest infections.

Functional Immunoglobulin Testing

Assessment of antibody response to vaccination (e.g., tetanus, pneumococcal, Hib) by comparing pre- and post-immunisation titres.

Cryoglobulins

Serum proteins that precipitate below 37 °C, forming immune complexes that can cause Raynaud’s, vasculitis, arthritis, or nephritis.

Raynaud’s Phenomenon

Triphasic colour change (white-blue-red) of extremities on cold exposure; common symptom in cryoglobulinaemia.

Purpuric Vasculitis

Leukocytoclastic vasculitis presenting with non-blanching palpable purpura; may arise from circulating cryoglobulins.

Cryofibrinogen

Cold-precipitable plasma fibrinogen complex, distinct from serum cryoglobulin; detected in EDTA plasma at 4 °C.

Immunofixation Electrophoresis (IFE)

High-resolution electrophoresis technique that identifies monoclonal immunoglobulin classes and light chains.

CSF Isoelectric Focusing (IEF)

Electrophoresis of paired CSF and serum on pH gradient agarose to detect intrathecal IgG synthesis (oligoclonal bands).

Oligoclonal Bands

Additional IgG bands in CSF but not serum, indicating antibody production within the CNS; seen in multiple sclerosis and infections.

Type 2 Oligoclonal Pattern

Presence of bands in CSF only, the classic finding of intrathecal IgG production.

Multiple Sclerosis (MS)

Autoimmune demyelinating disease; oligoclonal bands support diagnosis alongside clinical and radiologic findings; treated with steroids, interferons, monoclonal antibodies.

Serum Protein Electrophoresis (SPE)

Laboratory method separating serum proteins into albumin and globulin fractions to detect paraproteins or inflammatory patterns.

Lectin Pathway of Complement

Cascade initiated by mannose-binding lectin (MBL) binding to microbial carbohydrates, activating MASP enzymes and C4/C2.

Biomedical Scientist (BMS)

Laboratory professional responsible for performing and supervising diagnostic tests, training, and quality in clinical pathology.

Immunology Day Centre

Clinical service providing on-site immunology expertise and oversight for laboratory test interpretation.

Immune Complex

Aggregate formed when antibodies bind antigens; can be measured by nephelometry/turbidimetry and may trigger inflammation.

Latex Enhancement

Use of latex-coated antibodies in nephelometric/turbidimetric assays to increase light scatter and assay sensitivity.

Angioedema (Complement-Related)

Swelling due to C1INH deficiency or dysfunction, resulting in excessive bradykinin production; low C4 is typical.