A frameshift error affecting multiple cytology cell blocks: Lessons from a near‐miss event

In this scenario, it was ultimately discovered that a “frameshift error” involving a total of 7 different cytology cases had occurred during the preparation of the cell block H & E slides (Fig. 1). Specifically, the cut cell block paraffin sections were sequentially placed onto an incorrectly paired prelabeled glass slide. It is tempting after an incident such as this to immediately place blame on an individual and apply corrective action at that level. However, adverse events are often the result of larger system-based issues. Even cases such as this, which may appear to be a clear-cut mistake at face value, provide a valuable opportunity to conduct further investigation and to perform a systematic process review to help to uncover larger systemwide vulnerabilities in the pathology laboratory. Although a major contributing factor of this case was the failure of the histotechnologist to properly match each cell block to the corresponding preprinted glass slides and verify patient identification before cutting, there were several other potential issues brought to light (see the Fishbone diagram in Fig. 2). In this case, the laboratory information system capabilities of our laboratory prevented the histotechnologist from being able to print individual slides on demand for each case via a bar code scanner to ensure specimen matching. As in many laboratories, batch printing of slides with manual slide-block matching is a necessary process to ensure some degree of efficiency and specimen throughput. The workflow at the time of the incident allowed laboratory service assistants to preprint blank slides for use by the histotechnologists. Slides were batch-preprinted for that day's cell block cases. These cases usually have consecutive or nearly consecutive accession numbers, which minimize visual differences in the labeled specimen numbers. At the time of this incident, trays with ice had been being used for cutting and separating cases. The cell block cassettes and respective slides were being placed in parallel with each other. In this case scenario, the histotechnologist ultimately failed to verify the patient identification (the correct cell block cassette number to the labeled blank-slide number). However, there were factors that may have been sources of distraction or pressure. For instance, the constant emphasis on turnaround time is a pressure that can contribute to laboratory errors. At the time of this event, the histology laboratory was-short staffed. That day, a new histotechnologist was being trained and needed close supervision. Per our laboratory protocols, cell blocks are prepared upfront for each cytology case (with some exceptions based on specimen type, such as thyroid fine-needle aspirations which do not have a cell block prepared upfront). IHC stains can also be ordered upfront, such as for rush cases. These are cut as unstained slides at the same time as the slides for H & E staining. While the blank slides for H & E remain to be stained in the histology laboratory, the unstained slides for IHC are sent to the IHC laboratory for further processing. If not cut upfront, the blank slides for IHC are cut on another day. As with most cytology specimens, the cell block itself inherently presents a unique challenge because of the lack of clearly distinguishable gross features such as color, size, and shape. As in surgical pathology cases, a paraffin block is formed and then cut to make an H & E slide. However, in contrast to surgical pathology specimens, the gross appearance of the cytologic material within the paraffin mold is much less variable or distinctive from case to case (Fig. 3). The paucity of clearly identifiable gross features for cytology cell blocks (as described above) can make the block-checking step before the release of H & E slides from the histology laboratory less effective for cell blocks in comparison with other specimens. This generally holds true regardless of the cell block preparation type and can be further compounded by other factors such as specimen cellularity. In comparison, even core biopsy surgical pathology specimens can vary in their placement in the mold and in the number of cores, and this may be further aided by other visual cues such as inking; these are all features largely lacking for cytology cell blocks (Fig. 3). The aforementioned challenges are true not only when the slide leaves the laboratory but also once it reaches the cytopathologist's microscope. The lack of distinctive features differentiating one cytology specimen from the next can make matching liquid-based or smear cytologic specimens to their corresponding cell blocks challenging, particularly when the material is scant or from similar sites. In the aforementioned case scenario, it was not until multiple specimens did not match that concern was raised. The 1 case that was finalized before the discovery of the frameshift error was a rush case. To facilitate a rapid turnaround time, the IHC stains had been ordered upfront. This caused those IHC slides to also be affected by the frameshift error because they were cut at the same time as the H & E slide. Had the IHC not been ordered upfront, they would have been cut the next day (and from the correct block). This case qualifies best as a near-miss event. An incorrect diagnosis of positive for malignant cells, which would have upstaged the second patient in the case scenario, was averted, and no harm was done to the patient. The other case had been signed out correctly as positive for malignant cells on the basis of the liquid preparation slide findings; although that case was originally signed out with a note that the cell block material was paucicellular, it was later amended to note that the correct cell block demonstrated high tumor cellularity adequate for ancillary studies. The other cases involved in the frameshift were not signed out before identification of the error, and as such, the final diagnoses were based on the properly matched liquid-based preparation slide and the corresponding cell block slide. Near-miss events, although occurring more frequently than those that cause serious harm, are often overlooked by safety leadership. In contrast to events that cause serious harm and thus mandate reporting and review, protocols for reviewing near-miss events are less standard. However, these events usually involve the same root causes that under different circumstances may have led to more serious harm. Thus, they provide an excellent opportunity for laboratories to perform a root cause analysis and investigate potential system issues. As a result of this investigation, several quality improvements have been made. One change is that cell block slides are no longer batched within the same ice tray but rather are interspersed with the surgical cases. Additionally, all cell blocks for a given day are no longer cut by the same histotechnologist. In conclusion, although patient safety issues overlap between the surgical pathology and cytopathology laboratories, there are unique challenges to the cytopathology laboratory. Tools such as root cause analyses are integral to identifying potential vulnerabilities before an incident and to identifying areas for targeted improvement after an incident has occurred. Quality assurance and quality improvement are a cornerstone of the cytopathology laboratory and should be viewed as an opportunity for growth and learning rather than focusing on blame. Disclaimer: This case is based on actual events at Beth Israel Deaconess Hospital in Boston, Massachusetts. Case details have been altered for educational purposes and to protect patient identity in accordance with the Health Insurance Portability and Accountability Act. No specific funding was disclosed. Paul A. VanderLaan reports personal fees from Gala Therapeutics, Intuitive Surgical, and Galvanize Therapeutics outside the submitted work. The other authors made no disclosures.