In our second installment, we continue our conversation from the June issue with pathologist Ken Mero, BS, MS DVM, PhD, of VetPath Services in Stone Ridge, N.Y., to learn when to consider special stains and how to help your pathologist help you.
What are special stains and when should they be requested?
Special stains are specialized procedures to identify specific cellular features using dyes with particular affinity for certain cellular constituents. Examples are Giemsa and toluidine blue, which have an affinity for mast cell granules, or silver stains for silver deposition on the cell walls of organisms such as fungi. Some are quick, single-step procedures, and others are complex, multi-step, labor-intensive and time-consuming techniques.
When should we request special stains?
When to perform a special stain and which one(s) is probably best decided by the pathologist, although the clinician could inquire about that possibility when the diagnosis is less specific than desired. A seasoned pathologist is likely to appreciate which cases might benefit from a special stain and those in which it is likely to be a waste of time and expense.
Special stains all have a cost due to the price of the special reagents. Some laboratories charge additionally for special stains, whereas others consider them (within reason) to be part of a normal case-workup and do not charge extra.
The latter is helpful since clients are often billed for the hospital and lab services at the time of patient discharge, and asking for more money from a client after the fact for another unanticipated lab procedure can be difficult.
The ultimate special stains are immunohistochemical, designed to identify specific cell-surface antigens usually involving antigen-antibody interactions with peroxidase labeling. These are usually best done in specialty labs. They have a wide spectrum of fresh reagents and can “read” them immediately after the immuno-staining is complete. These usually have a significant cost, but they are helpful to identify undifferentiated cell types devoid of characteristic or diagnostic features with standard or special histologic staining.
Why does it take so long to get a report back?
“So long” is often a perception rather than a reality. In fact, even “longer than expected” is generally short compared to the delivery of similar services by pathologists in human medicine. Consider the few days to get a case finalized by a veterinary pathologist compared to a few weeks from an MD pathologist, although the process is the same.
The length of time for diagnostic reporting is determined by many factors. Perhaps most influential is the size and type of tissue. Many require an interval of supplemental fixation upon receipt at the lab, which adds a few days to the turnaround time. Processing improperly fixed tissue is a waste of time since it does not cut well on the microtome and is more difficult for the pathologist to read, increasing the likelihood of interpretive error.
Other specimens require decalcification. The duration depends on the size and density of the bone. There are rapid decalcifying agents, but here slower is usually better, since they achieve the demineralization with less alteration of cytomorphology.
Again, this leads to a better histologic specimen and the probability of a more accurate diagnosis. The size of the specimens once prepared at the laboratory for histologic processing determines whether they can undergo a quick processing in a few hours or the more standard processing, which is overnight.
Still other tissues may require an even lengthier processing (i.e. bones, brains and eyes). Some specimens, such as heart, brain and bone, may require that the pathologist dissect and/or photograph the specimen for the localization of lesions.
Also influencing how rapidly a specimen can be processed is the time of day that it arrives at the lab, whether delivered by the lab’s own courier or an independent contract carrier. Even these deliveries are sometimes delayed by weather, traffic jams and vehicle malfunctions.
Aside from the logistical and technical aspects affecting histologic preparations, many labs (both large and small) hire pathologists as independent contractors who do not work in the central facility, necessitating that the finished slides be sent to them. This is usually prompt with overnight priority delivery but still adds a day to the turnaround time. Nevertheless, if your favorite pathologist is one of those who works on the periphery, it may be worth the extra day’s wait.
The best of both worlds is when there is at least one pathologist in the central facility to handle STAT cases, even if it is just for a preliminary diagnosis offered before your primary preferred pathologist prepares your final document with all the bells and whistles the next day.
What is a rapid analyzer and how does it help?
A rapid analyzer is a quick processing scheduled on a programmable auto-processor. It is great for small specimens, which arrive at the lab already thoroughly fixed in formalin, quick to prepare for processing and more rapidly going through all of the processing steps, each of which is shortened.
This is most appropriate for endoscopic biopsies and exceptionally small specimens of other types, which don’t require intermediate steps, such as decalcification.
What should you do if you doubt the biopsy results?
Without a moment’s hesitation, get in touch with your pathologist. Some lesions are not an easy diagnosis on the first evaluation and there are many possible extenuating circumstances, such as plane of section, specimen orientation in the paraffin block, a small lesion that may not have been obvious during initial specimen gross sectioning for histologic processing, or the pathologist’s lack of knowledge of what he/she is supposed to be looking for when there is no clinical history.
An interested and conscientious pathologist is willing to re-visit a case in many ways. This may include double-checking the jar label to confirm patient identification, a second look at the gross specimen, re-orienting a specimen in the paraffin block, and/or requesting additional sections.
Sometimes, many sections of necrotic specimens are required in an attempt to find at least a small focus of viable cells for evaluation. Also, the pathologist might be forced to make assumptions in the absence of history or knowledge of patient demographics or site of the lesion, which can influence diagnosis.
Therefore, two heads being better than one, contacting your pathologist about a questionable diagnosis opens the door for an exchange of information greater than can be easily written on a test request form. A discussion including all aspects of the case may indeed influence a pathologist’s diagnosis or prognosis. It can also indicate how to proceed next: section re-cuts, special stains or immunohistochemistry. And if a pathologist implies infallibility or is uncooperative, find yourself another one.
Dr. Phil Zeltzman is a mobile, board-certified surgeon near Allentown, Pa. His website is www.DrPhilZeltzman.com. He is the co-author of “Walk a Hound, Lose a Pound” (Purdue University Press).