Description of the blood test:

IgG4 is the least common of the four subclasses of Immunoglobulin G. Unlike other antibodies that trigger strong inflammatory responses to kill bacteria, IgG4 is often “anti-inflammatory” and acts as a buffer in allergic reactions. However, in the last two decades, it has become famous as the primary marker for IgG4-Related Disease (IgG4-RD)—a condition where immune cells infiltrate various organs, causing them to become inflamed, enlarged, and eventually scarred (fibrotic).

What Does the Test Represent?

• Goal: To measure the specific concentration of the IgG4 subclass in the blood.
• Main Application: Diagnosing IgG4-Related Disease, which can mimic tumors in the pancreas, salivary glands, or kidneys. It is also used to monitor response to steroid therapy.
• Method: Nephelometry or Turbidimetry.

Collection Recommendations (General)

• Timing: Best performed in the morning.
• Fasting: Overnight fasting (8–12 hours) is recommended; plain water is allowed.
• Material: Venous blood (serum).
• Specific Rules: Avoid alcohol for 24 hours before the test. Inform your doctor if you are currently taking corticosteroids, as they can rapidly lower IgG4 levels and lead to a false-negative result.

Factors Influencing the Result

• Factors Altering Levels: Chronic allergies (like asthma or eczema) and parasitic infections can naturally cause a moderate increase in IgG4.
• Diagnostic Limitations: About 30–40% of patients with biopsy-proven IgG4-Related Disease may still have normal blood levels of IgG4, meaning a normal result doesn’t completely rule out the disease.
• Malignancy: Some types of cancer can cause secondary elevations in IgG4, which is why clinical correlation is vital.

When to Take This Test?

• Recommendations: If imaging (CT/MRI) shows an unexplained enlargement of the pancreas (autoimmune pancreatitis), salivary glands, or “tumors” in the eye sockets or kidneys that do not look like typical cancer.
• Importance: This test helps distinguish between a condition that requires surgery (cancer) and a condition that can be treated with medication (IgG4-RD).

Medical Interpretation

• Crucial Note: The interpretation of IgG4 levels is a highly specialized clinical task. An elevated IgG4 is a “clue,” not a definitive diagnosis. Only a specialist can “fine-tune” these results by correlating them with imaging and tissue biopsies.
• Significantly Elevated (>135–140 mg/dL): Highly suggestive of IgG4-Related Disease, especially if multiple organs are involved.
• Moderately Elevated: Can be seen in chronic allergic conditions, cystic fibrosis, or certain infections.
• Decreasing Levels: Usually indicates a positive response to treatment (e.g., prednisone or rituximab).

Possible Further Investigations

• Tissue Biopsy: The gold standard for confirming IgG4-RD (looking for specific patterns of “storiform fibrosis” and IgG4-positive cells).
• CT/PET-CT Scan: To identify all organs affected by the inflammatory process.
• Total IgG and other Subclasses: To see the broader immune context.
• ANCA and ANA: To rule out other forms of vasculitis or autoimmune diseases.
• Consultation with a Rheumatologist or Gastroenterologist.

When Does the Next Step Make Sense?

• If IgG4 is high and imaging shows organ involvement, the next step is often a biopsy to confirm the diagnosis and prevent permanent organ scarring. Because IgG4-RD mimics cancer, getting this test can sometimes prevent unnecessary major surgeries.
• All clinical decisions must be made by a healthcare professional based on the specific organ involvement and laboratory findings.

👉 If necessary, you can discuss the analysis results with a specialist such as a rheumatologist (Doctors – TAMC), gastroenterologist (Doctors – TAMC).