What is the role of lab testing in the diagnosis of Pneumocystis jiroveci pneumonia (PJP)?

Updated: Apr 24, 2019
  • Author: Shelley A Gilroy, MD, FIDSA; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Answer

Answer

A lactic dehydrogenase (LDH) study is performed as part of the initial workup. [24] LDH levels are usually elevated (>220 U/L) in patients with P jiroveci pneumonia (PJP). They are elevated in 90% of patients with PJP who are infected with HIV. The study has a high sensitivity (78%-100%); its specificity is much lower because other disease processes can result in an elevated LDH level.

LDH levels appear to reflect the degree of lung injury. They should decline with successful treatment. Consistently elevated LDH levels during treatment may indicate therapy failure and a worse prognosis.

Quantitative PCR for pneumocystis may be useful in distinguishing between colonization and active infection. [25]

Sputum P jirovecii PCR testing may be a viable alternative to invasive testing. This could be a more timely method for sample collection and would provide a safer alternative to bronchoscopic evaluation in patients who already have respiratory failure. Further studies comparing the sensitivity, specificity, and positive and negative predictive values for each sample type are needed. [26]

β-D-Glucan (BDG) is a cell-wall component of many fungi, including Candida, Aspergillus, and Pneumocystis (but not the Zygomycetes). It has been shown to be a sensitive test to detect PJP in a meta-analysis of 13 studies assessing the sensitivity, specificity, and overall accuracy of the test. A negative serum BDG result is sufficient for excluding PJP only in patients with HIV infection. In non-HIV cases, the results should be interpreted in parallel with clinical and radiologic findings. [27]


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