The tissue sample is cut up and prepared in the surgical theatre, moved to the further preparations gross room or the pathological laboratory, and finally sent to the manufacturer’s own laboratory or those recommended by the manufacturers for analysis. Several factors, both process dependent and operator dependent, contribute to error in this chain. The reported frequency of diagnostic errors in oncologic pathology depends on definitions and detection methods, and ranges from 1% to 15%. The large majority of diagnostic errors do not result in severe harm, although mild to moderate harm in the form of additional testing or diagnostic delays occurs in up to 50% of errors (1).
Pathology laboratories traditionally have considered two types of error: errors of accuracy and errors of precision of the test itself (2). Accuracy is the closeness of a measure to its true value, and precision is the degree to which repeated measures show the same results. But, there are additional process- and operator-dependent related errors that may affect patient safety, such as identification errors, specimen defects or contamination, and delays. In a study where surgical pathology amendment reports were analysed in a university hospital in the USA it was noticed that amendments (changes, corrections) were made to approximately five reports out of 1000. About one fifth of them were due to misidentifications (e.g. attribution of specimens to the wrong patient), one out of ten were due to specimen defects (e.g. lost or inadequate size of specimen), a quarter were due to misinterpretation (e.g. false negative), and almost half were due to reporting defects (e.g. dates, diagnostic codes) (3).
In summary, approximately 1/1000 patients and 2–4/1000 surgical pathology specimens end up being misidentified or having incorrect labels in the report.
Studies: Anecdotal evidence indicated that identification errors are frequent (4). Identification errors were studied in a prospective study including 136 laboratories from several countries (5). Of the 427 255 cases reviewed, 1811 had some type of mislabelling (0.4%). The entire case was mislabelled in 1.1/1000 (490) cases, 1/1000 specimens were mislabelled (796 specimens of 358 cases), 1.7/1000 blocks were mislabelled (2172 blocks in 461 cases) and 1/1000 slides were mislabelled (2509 slides in 502 cases). Misidentification of cases and specimens occurred most often at collection or at accessioning (i.e. when specimens are received, sorted, and entered in the laboratory). In 1751 out of the 1811 mislabelled cases (97%) the mislabelling was corrected without any additional consequences. In 59 cases (3%) a correction report was issued, and in 24 cases (1%) patient care was affected some way. Another retrospective study examined quality control records for an 18-month period and identified mislabelled surgical specimens. Out of 29 500 specimens 2.5/1000 were mislabelled (6). A prospective cohort study with 21 300 surgical specimens noted that 4.3/1000 specimens were incorrectly labelled. Reasons were, in order of frequency: not labelled at all, empty container, laterality incorrect, incorrect tissue site, incorrect patient, no patient name, and no tissue site (7). The majority of routine practices for identification and labelling probably underestimate the frequency of occurrence of errors, and many errors probably go undetected (4). Errors detected before patient harm or inconvenience has occurred are often called near misses.
Significant and worrisome levels of contamination of non-primate genome assemblies with human DNA sequences have been noted (8).