The definition of special stains
"Special stain" is an expansive term used for both chargeable and nonchargeable studies. Chargeable special studies are defined as add-on studies. In fact, the most common special study is nonchargeable and is known as leveling the block. Leveling the block obtains additional slides stained with H&E to ensure that the tissue examined on the microscope slide is fully representative of the disease process. This service is considered to be part of the H&E diagnosis and is not compensated.
In the Capital Digestive Care LLC laboratory, additional levels on the block have increased the adenoma detection rate by approximately 2% (personal observation). In cases of malignancy, Capital Digestive Care often obtains 30 additional slides to ensure complete sampling of the lesion and preservation of precious tissue in case additional studies are necessary. These studies are used to evaluate site of origin, prognostic factors such as vascular invasion, and expression of mismatched repair proteins as surrogate markers to microsatellite instability lesions and Lynch syndrome.
A common situation where a special stain is useful is in the diagnosis of Helicobacter pylori infection. The use of special stains is not unique to Helicobacter. There is a legion of other diagnoses that require special stains to reveal them, differentiate them from mimics, confirm their existence, or eliminate them as a possibility. An exhaustive listing of special stains and their uses is beyond the scope of this article. However, anexample is the use of additional studies to differentiate various forms of peripheral nerve sheath tumors, or to differentiate hyperplastic polyps from serrated polyps, or in the classification of mature B-cell lymphomas, or the use of the homeobox antigen CDX2 to identify an adenocarcinoma as being of intestinal phenotype.
In seeking to detect Barrett’s esophagus, Harrison et al.4 recommend eight separate biopsies as the best chance to come to an accurate diagnosis of intestinal metaplasia. In many cases, it is difficult for an endoscopist to retrieve eight biopsies from patients in whom Barrett’s esophagus is suspected. The conscientious pathologist will perform extensive leveling of the block and use ancillary studies such as Alcian blue to highlight rare goblet cells or differentiate pseudogoblet cells from true goblet.5
The add-on study is chargeable if reported as "negative for" or "positive for" a particular diagnosis. As an example, the ancillary study for Helicobacter is correctly interpreted as positive for Helicobacter or negative for Helicobacter. The add-on confers the ability for precise classification of disease. The positive interpretation indicates Helicobacter as an etiology, and a negative interpretation excludes Helicobacter as an etiology. Many pathologists substitute the term noncontributory for "negative for." This is incorrect. Negative information contributes to the final diagnosis because it excludes diagnostic possibilities and therefore is contributory. If the ancillary study truly does not contribute to the final diagnosis, then the noncontributory service should not have been done and is nonchargeable.
Ancillary studies increase sensitivity and specificity
Traditionally, pathologists performed a gross examination and examined large segments of tissue and sampled areas that were abnormal to sight and touch. When biopsies are obtained by endoscopy, it is the gastroenterologist who performs the gross examination during endoscopy. In this setting, the pathologist is blind to the gross appearance of the lesion. Nevertheless, the pathologist is called on to render a complete interpretation and is dependent on the eyes and hands of the gastroenterologist to procure a diagnostic sample. It is evident that in the modern setting, such a sampling is inherently limited and requires the pathologist and gastroenterologist to work as an integrated team to render a complete interpretation.
In the best of circumstances, the biopsy is small and in some cases it is an incomplete representation of a disease process. The pathologist is under considerable pressure to arrive at a correct and timely diagnosis because his or her interpretation potentially has substantial consequences to patient care. Ancillary studies or special stains enhance the ability to finesse information out of a small biopsy. The small size and incompleteness of the biopsy often result in disagreements of interpretation by pathologists. It is not uncommon for the gastroenterologist to encounter disagreements among pathologists in biopsy interpretation. Special stains often minimize disagreements because there are objective standards by which opinions become fact.
Lack of gold standard
Pathology literature often documents large interobserver variability in which two or more pathologists cannot agree on the diagnosis. There is also intraobserver variability in which the same pathologist on different days may arrive at a different conclusion. As the diagnosis moves from overt manifestation of disease to subtle alterations indicating the likelihood of disease development, this interobserver variability increases, and it is evident that the likelihood of diagnostic error increases. As the pathologist moves further up the diagnostic stream and closer to the point of disease origin, the morphologic markers are often obscure and little differentiated and require increasingly powerful tools to extract information. These tools are known as add-on or special studies.
