IgG2 as an independent risk factor for mortality in patients with community-acquired pneumonia.

Background: Mortality in patients with community-acquired pneumonia (CAP) remains high despite improvements in treatment.

Objective: To determine immunoglobulin levels in patients with CAP and impact on disease severity and mortality.

Methodology: Observational study. Hospitalized patients with CAP were followed up for 30 days. Levels of immunoglobulin G (IgG) and subclasses, immunoglobulin A (IgA) and immunoglobulin M (IgM) were measured in serum within 24 hours of CAP diagnosis.

Results: Three hundred sixty-two patients with CAP were enrolled -172 ward-treated and 190 intensive care unit-treated. Intensive care unit-treated patients had significantly lower values of IgG1, IgG2, IgG3 subclasses, and IgA than ward-treated patients. Thirty-eight patients died before 30 days. Levels of IgG2 were significantly lower in non-survivors than survivors (P=.004) and IgG2 <301 mg/dL was associated with poorer survival according to both the bivariate (hazard ratio 4.47; P<.001) and multivariate (HR 3.48; P=.003) analyses.

Conclusions: Patients with CAP with IgG2 levels <301 mg/dL had a poorer prognosis and a higher risk of death. Our study suggests the usefulness of IgG2 to predict CAP evolution and to provide support measures or additional treatment.