A floater is a type of extraneous tissue and foreign to the case. They are not found in the tissue block. Contaminants in the tissue block, i.e. paraffin block, are known as "pick-up" and, generally, are assumed to result from conditions at the grossing bench.
Floaters are considered to be near-misses, as they can lead to misdiagnoses if not identified as such. They are considered to be an indicator of (poor) quality.
- Tissue that is confidently identified as a floater and benign is typically identified as such on the slide and otherwise ignored.
- Example: a fragment of benign colon on an endometrial biopsy seen only on one level.
- Tissue that cannot be definitely identified as a floater may require identity testing, using short tanden repeat (STR) DNA testing.
- Malignant tissue that is apparently foreign to the case should be worked-up and reported.
- Platt, E.; Sommer, P.; McDonald, L.; Bennett, A.; Hunt, J. (Jun 2009). "Tissue floaters and contaminants in the histology laboratory.". Arch Pathol Lab Med 133 (6): 973-8. doi:10.1043/1543-2165-133.6.973. PMID 19492892.
- Layfield, LJ.; Witt, BL.; Metzger, KG.; Anderson, GM. (Nov 2011). "Extraneous tissue: a potential source for diagnostic error in surgical pathology.". Am J Clin Pathol 136 (5): 767-72. doi:10.1309/AJCP4FFSBPHAU8IU. PMID 22031316.
- Gephardt, GN.; Zarbo, RJ. (Nov 1996). "Extraneous tissue in surgical pathology: a College of American Pathologists Q-Probes study of 275 laboratories.". Arch Pathol Lab Med 120 (11): 1009-14. PMID 12049100.
- Smith, ML.; Raab, SS. (Nov 2011). "Assessment of latent factors contributing to error: addressing surgical pathology error wisely.". Arch Pathol Lab Med 135 (11): 1436-40. doi:10.5858/arpa.2011-0334-OA. PMID 22032570.
- Mosse, CA.; Stumph, JR.; Best, DH.; Vnencak-Jones, CL. (Sep 2009). "A B-cell lymphoma diagnosed in floater tissue: implications of the diagnosis and resolution of a laboratory error.". Am J Med Sci 338 (3): 248-51. doi:10.1097/MAJ.0b013e3181a88dc0. PMID 19745614.