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Pneumocystis PCR: It Is Time to Make PCR the Test of Choice
Laura Doyle1, Sherilynn Vogel1, Gary W Procop1
1Section of Clinical Microbiology, Department of Laboratory Medicine, Pathology and Laboratory Medicine Institute, Cleveland Clinic, Cleveland, Ohio.
Insights
Polymerase chain reaction (PCR) significantly increased Pneumocystis detection compared to toluidine blue staining. PCR is the most sensitive diagnostic test for Pneumocystis, aiding in differentiating colonization from true infection.
Area of Science:
- Medical Diagnostics
- Infectious Diseases
- Microbiology
Background:
- Cleveland Clinic shifted Pneumocystis testing from toluidine blue staining to PCR.
- Study aimed to compare positivity rates of these assays and with cytology/surgical pathology.
Purpose of the Study:
- Evaluate the diagnostic performance of PCR for Pneumocystis detection.
- Compare PCR with traditional methods like toluidine blue staining, cytology, and surgical pathology.
- Differentiate Pneumocystis colonization from true disease using PCR and clinical data.
Main Methods:
- Retrospective review of all Pneumocystis test orders one year before and after PCR implementation.
- Comparison of PCR results with concurrent cytology and surgical pathology findings.
- Medical record review for patients with rare PCR-detected Pneumocystis to assess clinical context.
Main Results:
- PCR showed a >4-fold increase in annual Pneumocystis detection compared to toluidine blue staining (3.0% vs 0.69%).
- PCR sensitivity surpassed cytology and was comparable to surgical pathology, detecting one additional case.
- Toluidine blue staining and surgical pathology demonstrated similar sensitivities and NPVs, superior to cytology.
Conclusions:
- PCR is the most sensitive method for Pneumocystis detection and is the recommended diagnostic test of choice.
- Integrating PCR results with clinical and radiologic findings helps distinguish true Pneumocystis infection from colonization.
Background:
The testing strategy for Pneumocystis at the Cleveland Clinic changed from toluidine blue staining to polymerase chain reaction (PCR). We studied the differences in positivity rates for these assays and compared each with the detection of Pneumocystis in companion specimens by cytology and surgical pathology.
Methods:
We reviewed the results of all Pneumocystis test orders 1 year before and 1 year after the implementation of a Pneumocystis-specific PCR. We also reviewed the corresponding cytology and surgical pathology results, if performed. Finally, we reviewed the medical records of patients with rare Pneumocystis detected by PCR in an effort to differentiate colonization vs true disease.
Results:
Toluidine blue staining and surgical pathology had similar sensitivities and negative predictive values, both of which were superior to cytology. There was a >4-fold increase in the annual detection of Pneumocystis by PCR compared with toluidine blue staining (toluidine blue staining: 11/1583 [0.69%] vs PCR: 44/1457 [3.0%]; chi-square P < .001). PCR detected 1 more case than surgical pathology and was far more sensitive than cytology. Chart review demonstrated that the vast majority of patients with rare Pneumocystis detected were immunosuppressed, had radiologic findings supportive of this infection, had no other pathogens detected, and were treated for pneumocystosis by the clinical team.
Conclusion:
PCR was the most sensitive method for the detection of Pneumocystis and should be considered the diagnostic test of choice. Correlation with clinical and radiologic findings affords discrimination of early true disease from the far rarer instances of colonization.
