IgG Subclass 1

What is IgG Subclass 1?

The most abundant IgG subclass, mainly targeting protein antigens such as those from viruses and bacterial toxins.

IgG has four subclasses, numbered 1 through 4, that each contribute differently to immune defense. IgG1 makes up the largest share of total IgG and is primarily directed against protein antigens, including those from viruses and bacterial toxins. Low IgG1 can contribute to an overall low total IgG and has been associated with increased susceptibility to certain infections. This subclass is typically tested as part of a full IgG subclass panel, ordered when recurrent infections or an abnormal total IgG raise questions about a possible immune deficiency. Subclass results are generally interpreted together as a group, alongside total immunoglobulin levels and infection history, rather than in isolation.

Tests often checked alongside this

• IgG (Immunoglobulin G) — the total antibody level this subclass contributes to
• IgG Subclass 2, 3, and 4 — typically reviewed together as a full panel
• IgA (Immunoglobulin A) — often checked alongside in an immune function workup

How this can show up in how you look and feel

• May be associated with recurrent infections if persistently low
• May be associated with fatigue

What can affect this marker

• Age
• Pregnancy
• Medications
• Infection
• Lab variability between testing methods

What to track over time

• Whether levels remain stable if monitoring a known immune concern
• How this subclass compares with the other three IgG subclasses over time
• Whether it correlates with infection frequency

What to ask your doctor

• How does this subclass level fit with my other IgG subclasses and total IgG?
• Could this be related to my infection history?
• Is any follow-up immune evaluation recommended?
• Should this be rechecked in the future?

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