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PCR helps non-HIV pneumocystis pneumonia diagnosis

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – Quantitative Pneumocystis jirovecii (Pj) PCR can be a valuable diagnostic tool in immunocompromised non-HIV patients, Swiss researchers report in a September 15th on-line paper in the European Respiratory Journal.

“The approach proposed,” Dr. Christian Garzoni told Reuters Health by email “not only has the potential to improve PCP diagnosis, but may also be directly applied in everyday clinical routine.”

Dr. Garzoni and colleagues at the University of Bern note that pneumocystis pneumonia (PCP) has been reported in nearly all drug-induced immunocompromised conditions. The clinical presentation is unspecific and the low disease incidence may lead to delayed diagnosis and increased mortality.

A PCP diagnosis requires pathogen identification in respiratory samples. PCR can detect Pj in respiratory samples with sensitivitiesas high as 96% and specificities more than 90% when compared with reference standard immunofluorescent (IF) antibody staining techniques. However, say the investigators it “is difficult to extrapolate from published data in HIV-positive patients to HIV-negative patients.”

To shed more light on the matter, the team retrospectively evaluated data on cases of definitive PCP diagnosed by positive IF testing of HIV-negative immunocompromised patients during a 10-year period.

Bronchoalveolar lavage fluid (BALF) material was available for testing in 71 cases. PCR in BALF detected Pj in all 71 patients, resulting in a sensitivity of 100.0%.

The team then went on to evaluate BALF from a random selection of 171 HIV-negative IF-negative adults who were tested for acute lung disease via BALF during the same period. In this group, PCR was positive in BALF from 18 patients (10.5%).

The researchers used these findings to establish that quantitative Pj PCR values beyond 1450 pathogens/mL had a positive predictive value of 98.0%. Values between 1 and 1450 pathogens/mL were associated with both colonization and infection and thus had no set differential cutoff. Diagnosis in these patients required IF and clinical assessment.

Overall, high values allowed reliable diagnosis, whereas negative PCR results virtually excluded PCP. Intermediate values require additional clinical assessment and IF testing.

Summing up, Dr. Garzoni concluded that “We think that our study has the potential to become a standard reference in the field, provide standardization of routine management of PCP diagnosis in immunocompromised HIV-negative patients, and provide clarity regarding the optimal diagnostic procedure in cases of PCP suspicion and also regarding the clinical relevance of molecular diagnostic tools for PCP.”

Reference:

Quantitative PCR to diagnose pneumocystis pneumonia in immunocompromised non-HIV patients

Eur Respir J 2011.