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 extr aneous tissue (contaminants) in surgical pathology. Design.-In 1994, p articipants in the College of American Pathologists Q-Probes quality i mprovement 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 pa rticipating laboratory. Participants.-Two hundred seventy-five surgica l pathology laboratories institutions, predominantly from North Americ a. Main Outcome Measures.-Extraneous tissue contamination rate for sli des in prospective and retrospective reviews; staffing and practice pr ocedures; 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 tiss ue (pathology laboratory, physician's office or operating room); and d egree of diagnostic difficulty caused by extraneous tissue.Results.-Th ree hundred twenty-one thousand seven hundred fifty-seven slides were reviewed in the prospective study and 57 083 slides in the retrospecti ve study. There was an overall extraneous tissue rate of 0.6% of,slide s (2 074/321 757) in the prospective study and 2.9% of slides (1 653/5 7 083) in the retrospective study. Of those slides with extraneous tis sue, 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 e xtraneous tissue in 12.2% of prospective cases and in 3.1% of retrospe ctive cases. Of the laboratories, 98% had written guidelines for chang ing solution in tissue processors, and 64.9% had guidelines for mainta ining water baths free of extraneous tissue. A total of 98.9% used len s paper, filter bags, or sponges for processing fragmented and small s pecimens. Written protocols for documentation of extraneous tissue in surgical pathology reports were established in 6.1% of laboratories, f or removal of extraneous tissue from blocks in 5.7%, and for removal o f extraneous tissue from microscopic slides in 4.7%. In 24% of laborat ories no comment or record was kept to document extraneous tissue. Ext raneous tissue consisted of neoplasm in 12.7% of the prospectively rev iewed slides and in 6.0% of the retrospectively reviewed slides. For t he prospective study, 59.4% of extraneous tissue was classified as sli de contaminants, and 28.4% was found to be contaminants within the par affin block; for the retrospective study, 72.9% was classified as slid e contaminants and 15.9% as block contaminants. For the prospective st udy, 63.2% of extraneous tissue was presumed to be from a different ca se, and in the retrospective study, 48.5% was presumed to be from a di fferent case; Over 90% of extraneous tissue was thought to originate f rom the pathology laboratory. The degree of diagnostic difficulty caus ed by extraneous tissue was judged to be severe in 0.4% of slides in t he 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 th e retrospective study, it could not be determined whether tissue in th e diagnostic sections was extraneous in 0.1%. Conclusions.-This study has documented the frequency, type, origin, source, and diagnostic dif ficulty of extraneous tissue and presents benchmarks of extraneous tis sue experienced in the general practice of surgical pathology.