Serum PCR of Pneumocystis carinii DNA in immunocompromised patients

The detection of Pneumocystis carinii DNA in serum, a potentially useful and attractive tool for the diagnosis of P. carinii infection and for monitoring the success of therapeutic interventions, remains a controversial issue. In a prospective study of 29 immunocompromised patients, including 16 with HIV infection undergoing bronchoscopy and bronchoalveolar lavage, we examined 32 bronchoalveolar lavage fluids and multiple serum samples for the presence of P. carinii DNA by using mitochondrial rRNA gene fragments pAZ102-E as pAZ102-H as primers. Samples from 7 immunocompetent patients were analysed as a control. 13/32 bronchoalveolar lavage fluids of immunocompromised patients (41%), but none of the controls, had both microscopic evidence of P. carinii cysts as well as P. carinii DNA detection. In none of these patients were serum samples obtained before therapy positive for P. carinii DNA, while in 1 patient (8%), P. carinii DNA was detected in 2/5 serum samples obtained during therapy. Interestingly, PCR detected P. carinii DNA in sera of 3/15 immunocompromised patients without detection of P. carinii DNA or organisms in BAL. Two of these 3 patients were taking secondary prophylactics for P. carinii pneumonia. In conclusion, PCR for P. carinii DNA in serum, at least in certain circumstances, may be of little value for the diagnosis of P. carinii pneumonia.