Granulomatous inflammation-an underestimated cause of false-positive diagnoses in lung fine-needle aspirates: observations from the college of american pathologists nongynecologic cytopathology interlaboratory comparison program

Arch Pathol Lab Med. 2010 Dec;134(12):1793-6. doi: 10.5858/2009-0491-CPR2.1.


Context: The false-positive rate for fine-needle aspirates of the lung has been cited as less than 1% for granulomatous inflammation, comprising one of the known causes of false-positive diagnoses.

Objective: To determine the rate of false-positive diagnoses of granulomatous inflammation for lung fine-needle aspirates by assessing the false-positive response rate in the context of the College of American Pathologists Nongynecologic Cytopathology Interlaboratory Comparison Program.

Design: We performed a retrospective review of 1092 participant responses for lung fine-needle aspirate challenges with the reference diagnosis of specific infections/granulomatous inflammation from 1998 to 2008 from the College of American Pathologists Nongynecologic Cytopathology Interlaboratory Comparison Program. False-positive rates by participant type (pathologist versus cytotechnologist), general diagnosis category, reference diagnosis, and preparation type were analyzed for the pathologists' responses.

Results: Of the 502 general category responses for pathologists, 428 (85.3%) were benign, 55 (11%) were malignant, and 19 (3.8%) were suspicious. There was no difference in the false-positive rate between preparations (P = .76) or participants (P = .39). Of those responses by pathologists that were benign, only 68.7% (292 of 425) were an exact match to granulomatous inflammation. Non-small cell carcinoma, adenocarcinoma, and squamous carcinoma represented 64% of false-positive/suspicious responses, while small cell carcinoma and carcinoid comprised 13%.

Conclusion: In an interlaboratory comparison program, granulomatous inflammation represents an important cause of false-positive/suspicious responses in lung fine-needle aspirates (14.8%) and is much higher than false-positive rates reported historically in clinical studies. These results highlight the importance of granulomatous inflammation as a mimic of carcinoma.

MeSH terms

  • Biopsy, Fine-Needle / standards
  • Carcinoma, Small Cell / diagnosis*
  • Cytodiagnosis / methods
  • Cytodiagnosis / standards
  • Diagnosis, Differential
  • False Positive Reactions
  • Granuloma / diagnosis*
  • Humans
  • Lung Neoplasms / diagnosis*
  • Pneumonia / diagnosis*
  • Predictive Value of Tests
  • Retrospective Studies