Chapter 13 - Laboratory diagnosis of Pneumocystis jirovecii pneumonia

Abstract

Pneumocystis jirovecii pneumonia (PcP) remains a major cause of respiratory illness among immunosuppressed patients. PcP is difficult to diagnose, in particular in non-HIV-infected patients due to the lack of specific clinical data associated. Since P. jirovecii could not be cultivated for many years, microscopic visualization of cysts or trophic forms in respiratory specimens based on cytochemical or immunofluorescence stainings are the standard procedures to identify this fungus. Polymerase chain reaction (PCR)-based methodologies have been developed to overcome the low sensitivity of microscopy in respiratory specimens, especially those with low fungal load, and in non-HIV-infected patients. Real-time quantitative PCR is the only format suitable for diagnosis since the risk of contamination is minimal and quantification is possible. Quantitative results have been used to differentiate PcP (high fungal load) from carriage/colonisation (low fungal load); however, this is inconclusive and has limited results in intermediate fungal loads. New strategies based on the measurement of blood biomarkers could be used to perform PcP diagnosis noninvasively. Several studies explored the usefulness of candidate serum biomarkers, such as (1–3)-β-d-Glucan (BG), Krebs von den Lungen-6 antigen (KL-6), lactate dehydrogenase (LDH) or S-adenosylmethionine (SAM), with the former presenting the most promising results.