Immunoglobulin and Serum Protein Analysis

Immunoglobulin and serum protein analysis is the laboratory measurement of antibody classes and the resolution of serum proteins to detect quantitative deficiencies, polyclonal increases, and monoclonal (paraprotein) bands. It supports the evaluation of immunodeficiency, chronic inflammation, and plasma-cell and lymphoproliferative disorders such as multiple myeloma.

Definition

Immunoglobulin and serum protein analysis comprises laboratory tests that quantify antibody classes and resolve serum proteins to characterise immune competence and to detect and type monoclonal proteins.

Scope

The topic covers quantification of immunoglobulin classes (IgG, IgA, IgM, IgE, and IgG subclasses), serum and urine protein electrophoresis, immunofixation, and free light-chain measurement. It is presented as a methodological and reference topic within clinical immunology.

Core questions

• How are total immunoglobulin levels and electrophoretic patterns used to distinguish deficiency, polyclonal, and monoclonal states?
• When is immunofixation or free light-chain measurement needed to characterise a monoclonal protein?
• How do reference intervals for immunoglobulin classes vary with age?

Key concepts

• Immunoglobulin classes and subclasses
• Serum protein electrophoresis and the gamma region
• Polyclonal versus monoclonal gammopathy
• Immunofixation and paraprotein typing
• Serum free light chains and the kappa/lambda ratio
• Hypogammaglobulinaemia

Mechanisms

Immunoglobulin classes are quantified by nephelometry or turbidimetry. Serum protein electrophoresis separates proteins by charge and size into characteristic regions; a discrete band in the gamma region suggests a monoclonal protein, which immunofixation then types by heavy- and light-chain class. Serum free light-chain assays measure unbound kappa and lambda chains and their ratio, adding sensitivity for light-chain-predominant processes. Reduced immunoglobulin levels point toward deficiency states, while diffuse increases indicate a polyclonal, reactive process.

Clinical relevance

These tests underpin the laboratory definition of monoclonal gammopathies and feed into diagnostic criteria for multiple myeloma and related plasma-cell disorders, and they help recognise antibody-deficiency states within the broader classification of inborn errors of immunity. The entry describes how the assays work and how patterns are interpreted at a population level, not how to manage an individual patient.

Epidemiology

Monoclonal gammopathy of undetermined significance becomes more common with age and is frequently detected incidentally on protein electrophoresis, which is why interpretation accounts for age and clinical context. Antibody-deficiency states are individually uncommon but are an important reason to quantify immunoglobulin classes.

Evidence & guidelines

Interpretation in this area is shaped by the International Myeloma Working Group criteria for plasma-cell disorders and by immunology references and classification frameworks for antibody deficiency. These define which protein measurements are recommended and the thresholds and patterns used to interpret them.

History

The resolution of serum proteins by electrophoresis in the mid-twentieth century, followed by immunoelectrophoresis and immunofixation, established the basis for detecting and typing monoclonal proteins. Quantitative immunoassays for immunoglobulin classes and, later, serum free light-chain assays progressively increased the sensitivity and specificity of the field.

Seminal works

• rajkumar-2014
• tangye-2022

Frequently asked questions

What is serum protein electrophoresis used for?

It separates serum proteins into bands and is used to detect deficiencies, diffuse polyclonal increases, and discrete monoclonal (paraprotein) bands that prompt further typing by immunofixation.

What is the difference between a polyclonal and a monoclonal increase in immunoglobulins?

A polyclonal increase reflects a reactive response from many antibody-producing clones, whereas a monoclonal increase reflects a single clone and appears as a discrete band, which warrants further characterisation.