Extraneous tissue in surgical pathology: a College of American Pathologists Q-Probes study of 275 laboratories.
OBJECTIVE
To develop a multi-institutional reference database of extraneous tissue (contaminants) in surgical pathology.


METHODS
In 1994, participants in the College of American Pathologists Q-Probes quality improvement program performed prospective and retrospective evaluations of extraneous tissue found in surgical pathology microscopic sections for a period of 4 weeks or until 1000 slides were reviewed in each participating laboratory.


METHODS
Two hundred seventy-five surgical pathology laboratories institutions, predominantly from North America.


METHODS
Extraneous tissue contamination rate for slides in prospective and retrospective reviews; staffing and practice procedures; location of extraneous tissue on slides; type of extraneous tissue (normal, abnormal, nonneoplastic, neoplasm, microorganisms, etc); class of extraneous tissue (slide or block contaminants); source of extraneous tissue (different or same case); origin of extraneous tissue (pathology laboratory, physician's office or operating room); and degree of diagnostic difficulty caused by extraneous tissue.


RESULTS
Three hundred twenty-one thousand seven hundred fifty-seven slides were reviewed in the prospective study and 57083 slides in the retrospective study. There was an overall extraneous tissue rate of 0.6% of slides (2074/321757) in the prospective study and 2.9% of slides (1653/57083) in the retrospective study. Of those slides with extraneous tissue, the extraneous tissue was located near diagnostic tissue sections in 59.5% of the slides reviewed prospectively and in 25.3% of slides reviewed retrospectively; deeper sections were performed to evaluate extraneous tissue in 12.2% of prospective cases and in 3.1% of retrospective cases. Of the laboratories, 98% had written guidelines for changing solution in tissue processors, and 64.9% had guidelines for maintaining water baths free of extraneous tissue. A total of 98.9% used lens paper, filter bags, or sponges for processing fragmented and small specimens. Written protocols for documentation of extraneous tissue in surgical pathology reports were established in 6.1% of laboratories, for removal of extraneous tissue from blocks in 5.7%, and for removal of extraneous tissue from microscopic slides in 4.7%. In 24% of laboratories no comment or record was kept to document extraneous tissue. Extraneous tissue consisted of neoplasm in 12.7% of the prospectively reviewed slides and in 6.0% of the retrospectively reviewed slides. For the prospective study, 59.4% of extraneous tissue was classified as slide contaminants, and 28.4% was found to be contaminants within the paraffin block; for the retrospective study, 72.9% was classified as slide contaminants and 15.9% as block contaminants. For the prospective study, 63.2% of extraneous tissue was presumed to be from a different case, and in the retrospective study, 48.5% was presumed to be from a different case. Over 90% of extraneous tissue was thought to originate from the pathology laboratory. The degree of diagnostic difficulty caused by extraneous tissue was judged to be severe in 0.4% of slides in the prospective study and 0.1% of slides in the retrospective study. In the prospective study, it could not be determined whether the tissue in the diagnostic sections was extraneous in 0.6% of slides, and in the retrospective study, it could not be determined whether tissue in the diagnostic sections was extraneous in 0.1%.


CONCLUSIONS
This study has documented the frequency, type, origin, source, and diagnostic difficulty of extraneous tissue and presents benchmarks of extraneous tissue experienced in the general practice of surgical pathology.
Gephardt
G N
GN
Department of Pathology and Laboratory Medicine, Promina Kennestone Hospital, Marietta, GA 30060, USA.
Zarbo
R J
RJ
D016208:Databases, Factual; D006801:Humans; D007753:Laboratories; D017063:Outcome Assessment, Health Care; D010340:Pathology, Surgical / Q000592:standards*; D011446:Prospective Studies; D011785:Quality Assurance, Health Care; D012189:Retrospective Studies; D012955:Societies, Medical; D014481:United States