The value of Pneumocystis carinii antibody and antigen detection for diagnosis of Pneumocystis carinii pneumonia after marrow transplantation.

Thirty-three marrow transplant patients with Pneumocystis carinii pneumonia were studied to determine the usefulness of antibody and antigen detection in the diagnosis of pneumocystis infection. Antibody against P. carinii was present in one half of all patients tested, and changes in antibody titer were not helpful diagnostically. P. carinii antigen was detected by counterimmunoelectrophoresis in the serum of 22 of 28 patients tested. Fifteen of 28 patients had antigen detected before or within 72 h after diagnosis. However, antigen was also present in 35 of 52 marrow transplant patients with viral or idiopathic pneumonia, in 11 of 25 transplant patients with no pneumonia, and in 22 of 28 other patients with pulmonary infiltrates. Only 1 of 50 normal marrow donors had detectable antigenemia. Detection of this antigen does not appear to establish the diagnosis of P. carinii pneumonia in the absence of other clinical or histologic data. The data may suggest that subclinical infection with this agent is more common than was previously recognized.