Pneumococcal antibody levels in patients with acute lung infiltrates.

We assessed the diagnostic value of serial serum antibody titers (IgG, IgM) to a polyvalent pneumococcal antigen preparation containing capsular polysaccharides from 14 different serotypes in the differential diagnosis between infectious lung infiltrates and lung infarction. A two-fold or higher change in antibody level, measured by means of an enzyme-linked immunosorbent assay (ELISA) was considered significant. Of 30 patients with pneumococcal pneumonia, 13 were infected with a Streptococcus pneumoniae serotype included in the vaccine (group A), five with a non-vaccine type (group B), and in 12 patients the S. pneumoniae serotype was not identified (group C). The sensitivity was 62% (group A). A heterotypic antibody rise was observed in one patient (group B). There was no difference in antibody rises between groups A and C. In 13 patients the pulmonary infiltrates were associated with different etiological factors (group D). The specificity determined in this group was 85%. The positive predictive value of an antibody rise was 89% (SD = 0.07) in pneumococcal pneumonia and a negative result signified in only 46% of the patients (SD = 0.10) that the pulmonary infiltrates were not associated with pneumococcal infection. Four patients suffering from pulmonary infarction had no antibody rise. Preliminary data of a current similar study, using a 23-valent antigen of pneumococcal capsular polysaccharides supported the aforementioned results. It is noteworthy that ten additional patients with lung infarction showed no seroconversion. The results suggest that serum antibody changes to a polyvalent pneumococcal vaccine may be of value in the differential diagnosis between infectious lung infiltrates and lung infarction.