Quality assessment of protected specimen brush samples by microscopic cell count

Area of Science:

• Medical Microbiology
• Pulmonology
• Diagnostic Cytology

Background:

• Protected specimen brushing (PSB) with quantitative culture is a reference method for diagnosing nosocomial pneumonia.
• Current diagnostic protocols lack established criteria for assessing PSB sample quality.

Purpose of the Study:

• To establish cytological criteria for evaluating the quality of protected specimen brushing samples.
• To correlate cell counts in PSB samples with quantitative culture results for improved diagnostic accuracy.

Main Methods:

• Analysis of inflammatory and bronchial cell counts per microscopic field (x500 magnification) in cytospin preparations of PSB samples.
• Comparison of cell counts and quantitative culture results between two study periods with modified PSB techniques and sampling sites.
• Inclusion of 86 samples from patients with suspected nosocomial pneumonia and 15 from uninfected controls.

Main Results:

• Samples collected in the second study period, using adapted techniques and peripheral sampling, showed significantly higher cellular content.
• No positive cultures were obtained from PSB samples with fewer than 10 cells per microscopic field.
• Cell counts in samples from uninfected controls were comparable to those from patients, suggesting cell presence indicates sample adequacy.

Conclusions:

• Absence or very low numbers of cells (<10 cells/field) in PSB samples likely indicate inadequate sample collection.
• Negative PSB cultures from samples with minimal cellularity should be interpreted with caution, and resampling may be necessary.