Application of Diagnostic Stewardship to Fungal Polymerase Chain Reaction: Low Yield of Follow-up Testing on Plasma and Bronchoalveolar Lavage After a Negative Result.

Background: Early diagnosis of invasive fungal disease is essential for optimizing management. Although the clinical utility of fungal polymerase chain reaction (PCR) testing on plasma and bronchoalveolar lavage (BAL) has been established, the role of follow-up testing remains unclear.

Methods: This was a retrospective single-center study. The yield of follow-up PCR for Aspergillus species, Mucorales agents, Fusarium species, Scedosporium species, dimorphic fungi, Pneumocystis jirovecii, and Candida species on plasma and/or BAL was measured at intervals of 1, 2, 3, and 4 weeks following a negative result.

Results: A total of 1389 follow-up tests on 406 plasma specimens from 264 patients and 983 BAL specimens from 431 patients were evaluated. Overall, the positivity rate at 1, 2, 3, and 4 weeks was 2.7% (4/148), 3.3% (4/123), 5.1% (4/78), and 3.5% (2/57), respectively, on plasma, and 0% (0/333), 0.3% (1/288), 0.4% (1/228), and 0.7% (1/134), respectively, on BAL. Conversions occurred with Aspergillus species, Mucorales agents, and Fusarium species PCR on plasma and Aspergillus species and P jirovecii PCR on BAL. All patients who converted were immunocompromised. Within 1 week of a prior negative test, 2 Aspergillus and 2 Mucorales PCRs were positive on plasma, and zero tests were positive on BAL. In week 1, only 1 Aspergillus species that was positive on day 7 was classified as probable fungal disease.

Conclusions: Fungal PCR follow-up testing on plasma and BAL within 4 weeks of a prior negative result was of low yield and rarely generated a positive result considered clinically significant in the first week.