Coagglutination and counterimmunoelectrophoresis for detection of pneumococcal antigens in the sputum of pneumonia patients.

Coagglutination was compared with counterimmunoelectrophoresis (CIE) for sensitivity and specificity in the detection of pneumococcal antigens in sputum. Initial sputum samples from patients with pneumococcal pneumonia (less than 12 h of antibiotic therapy) were positive for antigens in 37 of 44 cases (84%) by either test. There was a decline in the number of positive results with sputum samples obtained during continuing antibiotic therapy, but the decline was greater with CIE (only 29% of samples were positive at 3 days of therapy) than with coagglutination (61% of samples were positive at 3 days of therapy) (P less than 0.05). Sputum from 3 of 11 patients (27%) and from 2 of 11 patients (18%) with nonpneumococcal pneumonia was positive for pneumococcal antigens by CIE and coagglutination, respectively, indicating a similar degree of non-specificity. Coagglutination produced the same results as CIE with sputum from patients with chronic bronchitis but without pneumonia; 9 of 23 of these patients were positive. Coagglutination was simpler to perform than CIE and required only a fraction (about 1/30) of the antiserum required for CIE. These advantages, plus the greater sensitivity of coagglutination with sputum samples obtained during antibiotic therapy, suggest that coagglutination is preferable to CIE.