Study Guide

What is the antonym of histology?

Histology is the study of all normal tissue both grossly and microscopically. It has been directly related to pathology, the study of all abnormal tissue. Since pathology is studying abnormal tissue, this could be indirectly an antonym of histology. Although pathology needs histology to do most of the manual labor before the pathologist can observe the tissue microscopically.

The field of histology is growing but the number of people entering the field is shrinking very rapidly.  Therefore the salary of histologist varies greatly.  A typical histologist fresh out of school with the ASCP (HT) certification will be hired at an hourly rate of 20.00-22.00.  This is the starting pay for someone living in New England.  After being employed in the field for 5 years the pay scale can also vary depending on what areas of histology a person has become proficient in, the more the better.  The average pay scale would be from $25.00 to $30.00 an hour.  After 10 consistent years in the field one will make between $30.00 to $50.00 an hour.  These figures will go up dramatically in the next ten years because, the median age for a histologist today is 55 years old.  This means that in 7-10 years 1/3 to 1/2 of the histology population will retire.  What do you think will happen when this takes place?  At this rate there will always be a shortage of histologist.  Last time I looked at this job market, there was 90 histology jobs within 50 miles of me.  If I call a recruiter today, then I could have a job tomorrow in most major cities across the country and maybe the world.

Receiving a histology specimen is the first step. A histologist or pathologist assistant will remove the sample from its shipping/transport container. The container may be a box, bag or cooler. If the specimen is frozen, it should be placed in a -20 or -80 freeze ASAP. Any written information that is included with the specimen should be reviewed to ensure the specimen and information are correct and matching.

Accessioning a specimen is the second step. A histologist or pathologist assistant will review the actual specimen and note the dimensions, shape, color and any details that the specimen may have. This step is repeated during the grossing step to note any cutting done by the histologist or pathologist assistant and to note what is being submitted for processing or freezing.

Grossing is the step that gets the specimen grossly cut for histology. Cassettes come in different sizes, so the correct cassette size is chosen during this step as well. A common size cassette is better if possible, but some times it will not be big enough for samples such as eyeballs or turtle eggs. Specimens that should not just be cut in order to fit into a cassette! For specimens that will have a surgical margin to examine, these margins are often split up into different cassettes. The surgeon will often mark the sides of the specimen and each marked side can be examined by a pathologist.

Processing the specimen is usually done one of three ways

1. paraffin processing

2. snap freezing

3. polymer embedding

For each of these steps procedures number in the thousands. A standard procedure for normal size specimens will be discussed for each. Keep in mind that the bigger the specimen, the longer each step will be in the procedure. If the specimen is small each step will be shorter. Expect the steps to increase just like discussed for fixation. You want a 1 to 15 ratio of tissue to fixative solution, likewise you want this ration for processing specimens. If you overload the machines, or containers if hand processing, the tissue will have horrible results and take extra time and care in the following steps. This slows workflow in the lab and all your histology and pathology friends will not be happy with you if you do this. If the blocks are not processed properly and then need to be cut a year or two later, you may not have detail of membranes or nuclei, they also may not stain with immunohistochemistry!

Paraffin processing is the most universal histology procedure. In all labs, this procedure is probably the one procedure that every lab does almost identically. If you learn it once you will not have a problem when going from lab to lab, you can always have expertise on this part of histology. If you are a histology student, or a pathology student, this is something you should learn to avoid difficulty when running your processor. Different manufacturers design processors differently, and the control panel will always try to be more flashy and user-friendly as new models are sold, none of these machines will give you better results. Hand processing is the supreme and best way to process, though the equipment is more extravagant than a simple processor. Hand processing is dangerous and needs to be approached like a true safety hazard. An expert will have no trouble, but a new histologist should be trained and watched before performing hand processing alone. Almost 100 percent of all labs do not hand process. It is old-fashioned and does take up a large amount of technician hours. Only a lab with excellent workflow can hand process. For this reason, and the fact that many histology labs are constantly understaffed in hospital settings, automated processors are the preference of histologist and pathologist everywhere.

Processors are machines that have to process the tissue and then clean themselves. Reagents in these machines are usually— Formalin, alcohol, xylene and paraffin. Some labs use substitutions for these steps, for various reasons such as safety, waste disposal, cost, time, processor manufacturer specifications, tissue types, melting temperature preferences, decalcification needs, species specific needs and many other reasons. The basic steps of Formalin, alcohol, xylene and paraffin relate to the basic needs of processing. These needs are as follows – Fixation, Dehydration, Infiltration. Fixation preserves the tissue. Dehydration removes all water from the tissue. Infiltration is the most complicated part of processing, and in the case of paraffin is usually performed with xylene followed by paraffin. The xylene can mix with both the alcohol and the paraffin and that is why it was chosen. It has no other purpose. Xylene substitutes have been around for many years now, and still many labs prefer xylene. Xylene is flammable and it is a neurotoxin, this is not shown as a hazard in the manner that histologist use it. In recent years safety has been a focus in most labs and new protocols have been put in place to ensure a safe working environment.

After processing embedding is the next step in histology. Embedding is an important and time sensitive step. Paraffin embedding involves use of embedding machines and cold plates. The embedding machines are paraffin dispensers with two large warm bins for specimens and molds. Cold plates, sometimes attached to embedding stations, are steel plates with a freezing pump system. Cold plates cool the paraffin rapidly to speed up the entire embedding process.

When you are embedding or directing someone else to embed remember that the mold should be warm, not cold, for good cutting. You want to overflow the mold, keep the cassette hot and put the cassette on the mold before the overflowing paraffin pours out of the mold, this will ensure the cassette holds the paraffin in place well and will not have air bubbles. Air bubbles ruin blocks and can cause future levels cut from the block to mismatch early levels due to the need to re-embed the specimen because of an air bubble. Small air bubbles will form in any tissue that has a cavity, such as a heart. These cavities can be filled most of the time, and care to do so will ensure proper cuts.

Another point of embedding is removing excess wax from the blocks. Most labs now use a warm block melter that is angled to allow the paraffin to drip down into a container. New histologist will melt on block at a time, and use care not to touch the warm plate to the cutting area of the block. More experienced histologist may melt several at a time to save time. This technique does not affect cutting, but the largest block sizes will not be melted 100% in the angled block face where block ID data is written. For this reason the writing surface is often again cleaned while cutting by more experience techs.

Block an embedded sample ready to be cut, often has 2 parts, a cassette being attached to it for fitting to a microtome and labeling purposes. For frozen this can also mean an embedding frozen piece of tissue.

Glossary

Grossing- the specimen being examined and recorded

Histology- the study of tissue.

Histotechnology- the lab science of preparing tissue for microscopic examination.

H&E- a stain that shows detail of the cell, contrasting nuclei from cytoplasm. This is by far the most common stain in the world for tissue. H&E stands for “Hematoxylin and Eosin”. Usually this stain follows similar protocols with the most notable variation being the addition of Phloxine to the Eosin. Phloxine will stain a deep red on some tissue components and is preferred by some doctors. Hematoxylin is a reagent that is prepared with much care, and needs to have time to ripen during the final phase of preparation. The process has been compared to making wine, though it is in fact a much less time-consuming task, and you cannot drink it. The hematoxylin and eosin are always filtered on a daily basis and before the first use.

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