Description of the blood test:

While a total IgG test measures the overall amount of “memory” antibodies, it can sometimes hide specific weaknesses. Immunoglobulin G is divided into four subclasses: IgG1, IgG2, IgG3, and IgG4. Each subclass has a different job—some are best at fighting bacteria, others at neutralizing viruses or reacting to allergens. A patient can have a perfectly normal total IgG level but be missing one specific subclass, leading to recurrent infections.

What Does the Test Represent?

• Goal: To measure the concentration of each of the four IgG subclasses to identify specific immune gaps.
• Main Application: Evaluating patients with “normal” total IgG who still suffer from frequent infections, and diagnosing conditions like IgG4-related systemic disease.
• Method: Nephelometry or Turbidimetry using subclass-specific reagents.

Collection Recommendations (General)

• Timing: Morning blood collection is preferred.
• Fasting: Overnight fasting (8–12 hours) is recommended; plain water is allowed.
• Material: Venous blood (serum).
• Specific Rules: Avoid alcohol and heavy exercise for 24 hours before the test. It is important to wait at least 4–6 weeks after a severe infection or a course of steroids to get an accurate “baseline” reading.

Factors Influencing the Result

• Age: Subclass levels are highly age-dependent. For example, IgG2 levels naturally stay low in children until they are about 2–5 years old, which is why young children are more prone to certain bacterial infections.
• Medications: Long-term use of corticosteroids or chemotherapy can selectively suppress certain subclasses.
• Genetic Predisposition: Some individuals have a genetic inability to produce specific subclasses (most commonly IgG2).

When to Take This Test?

• Recommendations: If you have recurrent respiratory infections (sinusitis, bronchitis, pneumonia), especially if they are caused by “encapsulated” bacteria like Streptococcus pneumoniae.
• Importance: This test explains why some people get sick despite having “normal” standard lab results. It is the “fine-tuning” of immune diagnostics.

Medical Interpretation

• Crucial Note: Interpreting subclasses is a highly specialized clinical task. The significance of a low subclass depends on the patient’s age and their ability to produce antibodies after vaccination. Only a specialist can “fine-tune” these results by correlating them with your clinical history.
• IgG1 & IgG3 Deficiency: Often linked to recurrent viral infections and some bacterial infections.
• IgG2 Deficiency: Most common; associated with a failure to fight bacteria with carbohydrate coatings (like those causing pneumonia or meningitis).
• Elevated IgG4: A specific marker used to diagnose IgG4-related disease (IgG4-RD), which can cause inflammatory masses in the pancreas, salivary glands, or kidneys.

Possible Further Investigations

• Vaccine Response Test: Checking if the body can produce antibodies after a Tetanus or Pneumococcal vaccine (the “gold standard” for checking immune function).
• Total IgA, IgG, IgM: To see the broad immune context.
• B-cell Phenotyping: A detailed look at the cells that produce these antibodies.
• Consultation with an Immunologist.

When Does the Next Step Make Sense?

• If a specific deficiency is confirmed, the next step involves targeted prophylaxis (like early antibiotics for infections) or, in severe cases, immunoglobulin replacement therapy. If IgG4 is high, imaging (CT/MRI) is usually required to check for organ inflammation.
• All clinical decisions must be made by a healthcare professional based on the frequency of infections and the antibody response profile.

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