Contamination of histologic sections with “floaters” is occasionally encountered both in cytology and surgical pathology. The presence of extraneous cells and/or tissue fragments can be quite vexing and creates an unexpected diagnostic dilemma. Failure to recognize extraneous tissue can lead to unnecessary treatments and/or repeat procedures. The ideal approach would be recognize the extraneous tissue fragment and discount it; however, the burden of proof belongs to the pathologist and it is often difficult to prove given the multiple variables involved with specimen preparation. Another problematic issue is the series of questions that arise after identification of these extraneous tissue fragments, including the following: where did this tissue come from and how should it be proven, is the procedure for tissue processing creating contamination, and how should this be documented? Here we aim to review and provide a road map f or addressing some of these quality issues that cytopathology laboratories can face.

In a 1994 Q-Probes study conducted by the College of American Pathologists (CAP), which included 275 laboratories and 321,757 slides in a prospective study arm, the authors identified “floaters” at a rate of 0.6% with more than half (59.5%) identified near the tissue being evaluated. A retrospective study arm was also included by the authors (including 262 laboratories and 57,083 slides) and a rate of 2.9% was identified, with more than half (53.2%) of the tissue being identified distant from the tissue being evaluated. The higher incidence in the retrospective study was not surprising since it involved a re-review of slides specifically targeting the identification of “floaters”. These tissue fragments were non-neoplastic in most cases (87.3% prospective, 94% retrospective); nevertheless, when pathologists were surveyed, the “floaters” did cause a severe degree of difficulty in 0.4% in the prospective study and 0.1% in the retrospective study. Only 6.1% of laboratories had written protocols for documentation of “floaters”. Methods included labeling the slide as “floater” (55%), comment in report (37%) and documented in a log book (6%). ¹ In a more recent 2011 study performed by Associated Regional and University Pathologists (ARUP) laboratories, a tissue contaminant rate of 0.01% was identified in a review of 521,661 slides (125,000 cases) reviewed for QA purposes over a 64 month period. In a prospective review of 1,000 slides, a tissue contamination rate of 1.2% was identified. ² The 17 year gap between these two studies gives an indication that “floaters” are a persistent problem despite advancing technologies. Additionally, they tend to be recognized and considered more problematic when it is close to the tissue being evaluated. Methods for assessing “floaters” vary but include histologic characteristics such as the proximity of the tissue fragment (e.g., distant fragments are more likely to be extraneous tissue), the plane of focus (e.g., “floaters” may be out of the plane of focus) and presence in the paraffin block (e.g., “floaters” may be in a single section and not present in the paraffin block, or present in the block and therefore on multiple sections). ^1,2 The presence in the block, however, may be more of an indication at which point in the process the tissue appeared (e.g., “floaters” in the block may be an indication that tissue contamination arose prior to or during paraffin embedding). This will be discussed in further detail below.