What tests are used to evaluate immune function?

Laboratory Tests for Evaluating Immune Function

The most comprehensive approach to testing immune function involves a combination of screening tests including complete blood counts, immunoglobulin levels, specific antibody titers, and lymphocyte subset analysis. 1

Initial Screening Tests for Immune Function

Humoral Immunity Assessment

• Serum immunoglobulin levels (IgG, IgA, IgM) - Quantitative measurement to detect abnormal levels of the three major immunoglobulin classes 1, 2
• Serum specific antibody titers - Measurement of antibodies against vaccines or natural exposure 1
• Antibody response to booster immunization - Functional test of B cell response 1
• Flow cytometry to enumerate B cells - Quantifies total B cell numbers 1

Cellular Immunity Assessment

• TREC newborn screening - Identifies T cell lymphopenia in newborns 1
• Flow cytometry to enumerate CD4 and CD8 T cells and NK cells - Quantifies major lymphocyte populations 1, 3
• Cutaneous delayed hypersensitivity - In vivo test of T cell function 1
• NK cell cytotoxicity - Measures natural killer cell function 1

Phagocytic Cell Assessment

• Complete blood count with differential - Identifies abnormalities in neutrophil numbers 1
• Neutrophil staining and morphology on peripheral blood smear - Evaluates neutrophil structure 1
• DHR reduction or nitroblue tetrazolium test - Assesses neutrophil oxidative burst 1

Complement Assessment

• CH50 assay - Measures total hemolytic complement activity 1
• AH50 assay - Evaluates alternative pathway hemolytic activity 1

Advanced Immune Function Tests

Advanced Humoral Immunity Tests

• B-cell subset analysis - Identifies naive and switched memory B cells 1
• In vitro immunoglobulin production - Assesses B cell function in response to stimuli 1
• Antibody response to bacteriophage φX174 - Specialized test for antibody function 1

Advanced Cellular Immunity Tests

• T-cell subset analysis - Identifies naive, memory, and activated T cells 1, 3
• In vitro proliferative response to mitogens and antigens - Measures T cell function 1
• T-cell cytotoxicity assays - Evaluates cytotoxic T cell function 1
• Intracellular cytokine staining - Measures T cell cytokine production 1, 4
• ELISPOT assays - Identifies functional antigen-specific cells 1

Advanced Genetic Testing

• Targeted gene sequencing - For specific suspected immunodeficiencies 1
• Whole-exome/genome sequencing - Comprehensive genetic analysis 1

Interpretation Considerations

Age-Related Variations

• Immunoglobulin levels vary significantly with age, with IgG and IgA generally increasing with age 1, 5
• Lymphocyte subset normal ranges differ between children and adults 1

Common Pitfalls

1. Sample handling issues - Improper handling can affect cell viability for flow cytometry 3
2. Isolated interpretation - Results should always be integrated with clinical findings 3
3. Transplacental IgG transfer - Maternal IgG can mask deficiencies in infants 1
4. Recent infections or vaccinations - Can temporarily alter immune parameters 6

Test Selection Algorithm

1. For suspected antibody deficiency: Start with serum immunoglobulin levels, specific antibody titers, and B cell enumeration
2. For suspected cellular deficiency: Begin with lymphocyte subset analysis and T cell functional studies
3. For suspected combined deficiency: Perform complete screening of both humoral and cellular immunity
4. For suspected phagocytic defect: Evaluate neutrophil count, morphology, and function
5. For suspected complement deficiency: Measure CH50 and AH50

Special Considerations

• Flow cytometry has become the cornerstone of immune function testing, allowing simultaneous assessment of multiple cell markers 3
• Dried blood spot testing for immunoglobulins offers a convenient screening option for patients ≥16 years of age 7
• Nutritional status significantly impacts immune function; deficiencies in essential amino acids, fatty acids, vitamins, and minerals can impair immunity 6

By systematically applying these tests based on clinical presentation, clinicians can effectively evaluate immune function and identify specific immunological disorders.