Is measuring Immunoglobulin A (IgA) levels useful in patients with an active infection?

Utility of IgA Levels in Patients with Active Infections

Measuring IgA levels is generally not useful as a diagnostic tool in patients with active infections, except in specific circumstances such as suspected immunodeficiency or when monitoring certain infections like toxoplasmosis or Helicobacter pylori.

General Principles of IgA Testing

IgA is one of the five immunoglobulin classes, comprising approximately 15% of normal serum immunoglobulins 1. While IgA testing has specific applications, it is not routinely indicated during active infections for several reasons:

• IgA levels often show polyclonal elevation during chronic infection and inflammation, reflecting a non-specific immune response 2
• Changes in IgA levels typically lag behind the clinical course of infection
• Most active infections are better diagnosed through direct pathogen detection methods

Specific Circumstances Where IgA Testing May Be Useful

1. Suspected Immunodeficiency

• Primary or Secondary Antibody Deficiencies
  • IgA deficiency may be associated with recurrent respiratory infections
  • Should be measured as part of a complete immunoglobulin panel (IgG, IgA, IgM) when investigating recurrent infections 2, 3
  • Low IgA levels alone may not require treatment, but complete evaluation is needed

2. Specific Infections Where IgA Testing Has Diagnostic Value

• Toxoplasmosis

  • IgA antibodies can serve as important markers of acute primary infection 4
  • IgA antibodies are absent in uninfected subjects and appear rapidly after primary infection
  • Complements IgM determination for diagnosis of acute toxoplasmosis

• Helicobacter pylori Infection

  • IgA antibody titers can be used to monitor treatment success 5
  • Decreasing IgA titers (along with IgG) after antimicrobial therapy can confirm eradication
  • Useful in the small percentage of patients who have raised titers in this immunoglobulin class only

• Chlamydia trachomatis Infection

  • Specific IgA antibodies may serve as a diagnostic tool for monitoring active chlamydial infection 6
  • IgA titers decrease rapidly after successful treatment, while IgG levels remain elevated

Approach to IgA Testing in Clinical Practice

1. Do not order IgA levels routinely during acute infections

   • Most acute infections are better diagnosed through direct methods (cultures, PCR, antigen testing)

2. Consider IgA testing as part of immunodeficiency workup when:

   • Patient has history of recurrent infections
   • Other immunoglobulin abnormalities are detected
   • Functional antibody responses are being assessed

3. For suspected immunodeficiency:

   • Measure baseline IgG, IgA, and IgM levels
   • Assess functional antibody responses (e.g., pneumococcal antibodies) 2
   • Consider immunoglobulin replacement therapy if IgG levels are <400 mg/dL with recurrent infections 3

Common Pitfalls in IgA Testing

• Misinterpreting elevated IgA levels during infection

  • Polyclonal increases in IgA are common in chronic infection and don't necessarily indicate a specific pathogen

• Overlooking the need for comprehensive immunoglobulin assessment

  • IgA should not be measured in isolation but as part of a complete immunoglobulin panel

• Failing to consider functional antibody responses

  • Quantitative levels alone may not reflect immune function; functional antibody testing is often needed

• Overreliance on IgA for diagnosis of active infection

  • Direct pathogen detection methods remain the gold standard for most infections

Conclusion

While IgA measurement has limited utility during most active infections, it can be valuable in specific scenarios such as immunodeficiency evaluation or monitoring certain infections. Clinicians should reserve IgA testing for these specific indications rather than ordering it routinely during infectious workups.