The age of automation finally dawns for histopathology

Ironing out the peaks and troughs of laboratory workflow, the benefits of automation now reach further than ever before The benefits of automation have long been the preserve of biochemistry and haematology, where availability of high-throughput random access analysers has made same-day results turnaround the expected norm. In histopathology, however, the labour-intensive nature of tissue preparation has traditionally led to the turnaround time for biopsy, surgical and post-mortem results being counted in days rather than hours - a situation which is compounded by the delays commonly inherent in the process of specimen review and sign-off.

For patients, this typically means a wait of some weeks before attending an appointment to discuss results - by which time, their condition may have deteriorated for want of immediate treatment. Technology does now exist, however, whose adoption - when combined with an overall change in working practices - offers the very real possibility of specimens being processed, reviewed and signed off the very day they are received.

The cornerstones of this potential ‘revolution’ are two new automated instruments from Sakura Finetek - the Tissue-Tek Xpress continuous rapid tissue processor and Tissue-Tek AutoTEC automated embedding system, marketed exclusively in the UK and Ireland by Bayer Diagnostics. Together, these unique and innovative instruments represent the first step towards complete automation of routine histopathology functions, from tissue processing right through to the preparation of slides for microscopy.

Continuous tissue processing: 120 blocks per hour
The Tissue-Tek Xpress is a high throughput system which completely automates the processes of dehydration, clearing and impregnation of tissue specimens which can be loaded continuously on to the system. Unlike traditional vacuum infiltration technology which usually requires specimens to be loaded in batches and left for processing overnight, the Tissue-Tek Xpress processes specimens in as little as one hour, with no sacrifice in terms of quality or changes in microscopic morphology. In fact, results are comparable to, if not better than, traditional processing.

The Tissue-Tek Xpress is capable of processing specimens at the rate of 120 per hour, and it is possible to load a basket holding up to 40 cassettes on to the system every 15-20 minutes. This creates the potential for specimens to be processed on the day they are received, smoothing out the dramatic peaks and troughs which have traditionally characterised routine Histopathology workflow. Biopsies and larger specimens can be processed at the same time.

Fast, efficient processing is achieved using just four proprietary reagents which are not based on Formalin or Xylene and therefore present no health and safety hazard to laboratory staff. Being ‘molecular-friendly’, these reagents also preserve DNA, RNA and proteins in the tissue block to a much greater extent than Formalin. The total volume of reagents used is substantially reduced when compared with traditional methods, and retort cleaning cycles are unnecessary.

Uniform sections
Production of standardised tissue sections is key to the speed of processing achieved by the Tissue-Tek Xpress. Special grossing tools have been created for use with the system, making it easy to produce sections of uniform thickness on a consistent basis. Use of these tools to achieve controlled and standardised grossing ensures consistent quality in tissue processing.

The tools set includes a board with an adjustable depth tissue well and a guide for the knife or surgical blade. The tissue wells provide an area for the placement of the tissue while a knife-guiding assembly keeps the cutting blade level. Once the tissue has been placed in the well and held in place via a tissue tamper the knife blade is placed in the guide and is used to cut the tissue, yielding tissue pieces of uniform thickness. This grossing board is ideal for the sampling of solid organs and tumours. Flat structures such as small tubular organs like the appendix, fallopian tubes and umbilical cord are dealt with by means of a specially-designed fork (pictured below) which holds the tissue in place in order to achieve sections of uniform thickness.

The Accu-Edge Grossing Fork comprises a handle and head supporting a double array of four tines. The gap between the tines is pre-determined to accommodate the required thickness of tissue sections, which are held in place while the blade is slid against the outer surfaces of the tool. The Grossing Fork is particularly useful for sectioning organs composed of layers of different structures that tend to slide over each other, such as the bowel and gallbladder.  Tissues that are soft and slippery, such as adipose tissue, or fatty tissues such as breast are easy to handle with this tool.

Dedicated microwave technology
Patented microwave technology is utilised by the Tissue-Tek Xpress to accelerate the diffusion of solvents into tissues. Unlike established methods which have traditionally been based on an adaptation of the kitchen microwave, however, this operates continuously at low wattage instead of pulsing high levels of microwave energy. This approach ensures that tissues are processed very gently and evenly, avoiding the dangers of over-heating which could potentially be damaging to specimens. Any size of tissue can be processed provided the thickness of the section is correct.

New reagents have been introduced to complement this process.  Instead of toxic agents, the system uses a mixture of acetone, isopropyl alcohol, polyethylene glycol, mineral oil and paraffin, in much smaller quantities than would traditionally be required.

Automated embedding
Total automation of the embedding process is accomplished by means of the Tissue-Tek AutoTEC Embedding System which uses Tissue-Tek Paraform Cassettes to produce blocks at the rate of 120 per hour. The unique Paraform material used to make cassettes has sectioning characteristics similar to those of paraffin, allowing cuts to be made right through the cassette insert following embedding without damaging knife blades. This material does not pick up stains, and also does not interfere with microscopic examination.

Use of Paraform cassettes greatly speeds up the embedding process. The grossed specimen is inserted into a frame in the required orientation, and secured in that position by pushing down the cassette lid prior to processing in the Tissue-Tek Xpress. After processing, the cassette is automatically pushed down into a correctly sized base mould by the embedding system.

The system can accept four magazines of up to 32 cassettes at a time, and these can be loaded continuously throughout the day. The magazines can be used as baskets directly from the tissue processor. The Tissue-Tek AutoTEC senses each cassette and automatically differentiates between biopsy and standard size cassettes. Each cassette is then placed in the proper size base mould, after which paraffin is precisely dispensed and cooling is activated to form a block. The cassette is then moved to one of four output doors which can be detached from the system and used as convenient holding trays during sectioning.

The process of embedding can therefore be transformed from one of the most labour-intensive activities in the laboratory to one which is completed automatically in a fraction of the time.

Banishing the bottlenecks
“Given the recruitment and retention issues which now beset most histology laboratories, it makes no sense for highly skilled laboratory staff to spend hours each day embedding and cutting up samples”, says Bayer’s Cellular Pathology Product Manager, Simon Cutts. “Traditionally, overnight processing has been required in order to ensure that all specimens, from large tissues to small biopsies, are processed to the highest quality standards. This creates a peak workload of embedding as soon as staff arrive in the morning, typically tying up two members of staff for as much as six hours. Perhaps five or six people may then be engaged in sectioning the resulting blocks as they are released from the embedding process. The workflow is characterised by bottlenecks, peaks and troughs.”

“By changing to an automated method of working in which specimens are continuously loaded for processing and embedding, the peaks and troughs can be eliminated and replaced by a steady workflow which can be handled by fewer people throughout the day”, he continues. “Adoption of the Tissue-Tek Xpress and AutoTEC systems therefore has a major impact on laboratory workflow, representing an entirely different method of working. Smoothing out the peaks can have a dramatic effect on staffing requirements, and this could be particularly beneficial for laboratories that have traditionally had to rely on costly agency staff.”

The potential impact of introducing this technology is far-reaching. Use of the Tissue-Tek Xpress and AutoTEC systems will provide pathologists with higher quality sections for examination due to standardisation in specimen thickness. For the first time, it is now possible to process specimens in about one hour without sacrificing quality or generating changes in microscopic morphology.

Same-day tissue processing really does open the way for same-day diagnosis and therapeutic decisions - which is good news for patients and also for trusts under pressure to meet government targets.

By Simon Cutts, Product Manager Cellular Pathology, Bayer Healthcare Diagnostics Division