1. Clinical Examination
The clinical examination is often the first step in diagnosing immune system disorders. A thorough history and physical examination can provide essential clues about potential immune dysfunction. Key points of focus include the patient’s symptom history, infection frequency, and the presence of autoimmune symptoms.
Key Aspects of Clinical Examination
- Medical History: A detailed patient history is essential. It should include:
- Frequency and severity of infections (e.g., frequent respiratory infections, recurrent skin infections).
- Family history of immune system disorders or autoimmune diseases.
- Presence of unexplained fever, chronic fatigue, or weight loss.
- Any history of allergies or anaphylaxis.
- Physical Examination:
- Lymph Nodes: Palpation of lymph nodes for enlargement, tenderness, or irregularities.
- Skin Examination: Assessment of rashes, lesions, or signs of autoimmunity (e.g., butterfly rash in lupus).
- Joints: Swelling, tenderness, or deformities in cases of autoimmune diseases like rheumatoid arthritis.
- Organomegaly: Enlarged spleen or liver, which may suggest an underlying immune disorder.
2. Blood Tests and Basic Laboratory Work
Laboratory tests provide crucial information about the function of the immune system. Many immune system disorders are identified through abnormalities in blood cell counts or specific immune-related proteins.
Complete Blood Count (CBC)
A CBC is a fundamental test used to evaluate the different components of the blood, including white blood cells (WBCs), red blood cells (RBCs), and platelets. This test is essential for detecting immune deficiencies, infections, and autoimmune disorders.
- Key Parameters:
- White Blood Cell Count: High WBC counts may indicate infection or inflammation, while low counts suggest immunodeficiency.
- Differential Count: Measures the percentages of different types of WBCs (e.g., neutrophils, lymphocytes, eosinophils) to identify specific immune responses.
- Platelet Count: Low platelets can indicate autoimmune conditions such as systemic lupus erythematosus (SLE).
C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR)
Both CRP and ESR are markers of inflammation. They are commonly elevated in autoimmune diseases such as rheumatoid arthritis, lupus, and vasculitis.
- CRP: Produced by the liver in response to inflammation; high levels are seen in active inflammation and infections.
- ESR: Measures how quickly red blood cells settle at the bottom of a test tube; a faster rate can indicate inflammation.
Serum Immunoglobulins (IgG, IgA, IgM)
Immunoglobulins are essential components of the immune system, produced by B cells to fight infections. Measuring their levels helps assess antibody deficiencies or immune hyperactivity.
- IgG: The most abundant antibody, providing long-term immunity. Low levels are seen in Common Variable Immunodeficiency (CVID).
- IgA: Protects mucous membranes. Low levels may indicate Selective IgA Deficiency, leading to recurrent respiratory and gastrointestinal infections.
- IgM: The first antibody produced during an immune response. Elevated levels can suggest acute infections or autoimmune diseases.
Autoantibodies
Autoantibody testing is crucial for diagnosing autoimmune diseases, where the immune system attacks its own tissues. Common autoantibodies include:
- Antinuclear Antibodies (ANA): Commonly elevated in systemic lupus erythematosus (SLE) and other autoimmune conditions.
- Rheumatoid Factor (RF): Found in many people with rheumatoid arthritis.
- Anti-cyclic Citrullinated Peptide (Anti-CCP): Highly specific for rheumatoid arthritis, often detected before symptoms develop.
- Anti-dsDNA and Anti-Smith Antibodies: Specific markers for lupus, helping to confirm diagnosis.
3. Immunologic Assays
Immunologic assays assess the function and response of the immune system by measuring specific immune components such as antibodies, T cells, and complement proteins.
Flow Cytometry
Flow cytometry is a powerful technique used to analyze the presence and function of immune cells, such as T cells, B cells, and natural killer (NK) cells. It is especially useful in diagnosing immunodeficiencies and monitoring immune system health.
- T-cell Count: Used to evaluate HIV/AIDS by measuring CD4+ T-cell levels.
- B-cell Count: Low B cells suggest antibody deficiencies like Severe Combined Immunodeficiency (SCID).
- Natural Killer (NK) Cells: NK cell function can be impaired in certain immunodeficiencies, such as Chediak-Higashi syndrome.
Complement Activity Testing
The complement system is a group of proteins that enhance the immune response by helping antibodies and immune cells clear pathogens. Complement activity testing evaluates the efficiency of this system, which is critical for identifying complement deficiencies.
- CH50 Test: Measures the overall activity of the complement system.
- C3 and C4 Levels: These specific components of the complement system can be low in autoimmune diseases like lupus.
4. Skin Testing
Skin tests are commonly used to evaluate allergic reactions and hypersensitivity responses. They help identify specific allergens responsible for symptoms.
Types of Skin Tests
- Skin Prick Test: Tiny amounts of suspected allergens are introduced into the skin using a small needle. A raised, red bump (wheal) indicates a positive reaction.
- Intradermal Test: Small amounts of allergens are injected under the skin to assess more sensitive reactions.
- Patch Testing: Used to diagnose contact dermatitis by applying allergens on patches to the skin and observing for delayed reactions after 48–72 hours.
5. Imaging Techniques
Imaging techniques are vital for detecting organ involvement in immune system disorders, particularly in autoimmune diseases where internal organs can be affected. Imaging helps monitor disease progression and guides therapeutic interventions.
Common Imaging Modalities
- X-Rays: Used to assess joint damage in rheumatoid arthritis or lung involvement in sarcoidosis.
- Ultrasound: Evaluates lymph nodes, spleen, and other soft tissues in conditions such as lymphoma or autoimmune hemolytic anemia.
- Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues and is particularly useful in diagnosing multiple sclerosis or assessing joint inflammation in rheumatoid arthritis.
- CT Scan: Used for detecting organ enlargement, abscesses, or malignancies associated with immune dysfunctions.
6. Genetic Testing
Genetic testing is becoming increasingly important in diagnosing primary immunodeficiency disorders. By identifying specific mutations, physicians can confirm diagnoses and tailor treatments accordingly.
Common Genetic Tests
- SCID Screening: Newborn screening detects genetic mutations that cause SCID, allowing for early intervention.
- Genetic Panels: Used to assess mutations related to various immune deficiencies, such as Chronic Granulomatous Disease (CGD) or Wiskott-Aldrich Syndrome.