What to Expect with New ELISA Assays for Immunobullous Diseases
Expires: December 16, 2022
Julia Lehman, M.D., is a Consultant in Dermatology and holds the academic rank of Associate Professor of Dermatology and Laboratory Medicine and Pathology at Mayo Clinic in Rochester, Minnesota.
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Transcript and References
Hi, I’m Matt Binnicker, the Director of Clinical Virology and Vice Chair of Practice in the Department of Laboratory Medicine and Pathology at Mayo Clinic. Did you know that the Mayo Clinic Immunodermatology Laboratory has offered ELISA for immunobullous diseases for over 15 years? In this month’s Hot Topic, Dr. Julia Lehman will discuss some important changes that are taking place in order to continue offering the highest quality testing. I hope you enjoy this Hot Topic, and I want to personally thank you for allowing Mayo Clinic the opportunity to be a partner in your patient’s health care.
Hello, I’m Dr. Julia Lehman, Director of the Mayo Clinic Immunodermatology Laboratory and a dermatologist/dermatopathologist at Mayo Clinic. I’d like to talk to you today about what to expect as we transition to a new vendor for our ELISA assays for autoimmune immunobullous dermatosis.
I have no disclosures.
Background—Autoimmune Blistering Diseases
Though rare, autoimmune blistering diseases, such as pemphigoid and pemphigus, can confer a considerable amount of pain and suffering to affected patients and can unfortunately contribute to increased mortality.
Background—Diagnosis of Autoimmune Bullous Diseases: Clinical Features
Patients with these immunobullous diseases may present with tense blisters or flaccid erosions, although other atypical clinical features may be observed. For example, the possibility of pemphigoid should be investigated in older individuals with generalized pruritus, even when a rash is not present, or in the setting of an urticarial skin eruption or pruriginous eruption that is not improving with conventional therapies. In patients with chronic mucosal ulcerations or skin erosions, it is prudent to evaluate for the possibility of pemphigus.
The diagnosis of immunobullous diseases requires integration of clinical features with findings on skin biopsy specimens submitted for standard microscopy and direct immunofluorescence, as well as serum studies for specialized testing.
Background—Diagnosis of Autoimmune Bullous Diseases: Histopathology
In pemphigoid, histopathologic changes may include eosinophil-rich subepidermal blister, which would be the most characteristic findings. However, changes may be more subtle, with only a sparse perivascular infiltrate with eosinophils, with or without intravascular neutrophils. The presence of eosinophilic spongiosis can be a helpful clue, although this finding is non-specific and can be seen in a range of other disease entities as well.
In pemphigus, the classic microscopic changes include acantholysis, or rounding up and separation of keratinocytes from each other. In pemphigus vulgaris, this process is often seen above the basilar layer of keratinocytes, or suprabasilar acantholysis, while in pemphigus foliaceus, this process typically affects keratinocytes high up in the epidermis. Often, the acantholysis in pemphigus foliaceus can be subtle and frequently is overlooked. While eosinophils and eosinophilic spongiosis can be observed in pemphigus, their presence is inconsistent.
Background—Diagnosis of Autoimmune Bullous Diseases: Direct Immunofluorescence
On direct immunofluorescence testing with pemphigoid, there is often linear deposition along the basement membrane zone with IgG and/or C3. While these features can support the diagnosis, they are also non-specific and can be seen in other subepidermal autoimmune blistering diseases, such as epidermolysis bullosa acquisita and bullous lupus erythematosus. In pemphigus, there is intercellular deposition with IgG, IgA, and/or C3. Subtyping of the particular form of pemphigus requires clinical correlation.
Background—Diagnosis of Autoimmune Bullous Diseases: Indirect Immunofluorescence
Indirect immunofluorescence is typically performed using human salt-split skin substrate and monkey esophagus substrate. In pemphigoid, linear deposits of IgG are observed at the roof of the induced blister with salt-split skin testing, while in pemphigus, this study is usually negative. On monkey esophagus substrate, linear deposition of IgG can be seen in pemphigoid and between mucosal epithelial cells in a chicken-wire type pattern in pemphigus.
Background—Diagnosis of Autoimmune Bullous Diseases: ELISA
Though clinical and microscopic features are required for diagnosis of pemphigoid and pemphigus, ELISA studies can improve diagnostic certainty. In addition, the literature supports their role in disease activity monitoring.
In particular, BP180 and BP230 are sensitive and specific for pemphigoid, while DSG1 and DSG3 are sensitive and specific for pemphigus. These tests may also be positive in rare conditions such as paraneoplastic pemphigus.
Results for ELISA testing for immunobullous diseases are semi-quantitative. That is, while the laboratory reports a numerical value as a result, the primary utility of the test is the interpretation of this numerical result as negative or positive, which is determined by reference ranges that are set by the kit manufacturer and corroborated in our own validation studies.
ELISA Assays for Autoimmune Bullous Diseases
For the last 15–20 years, we had used the same vendor for our ELISA assays. In recent times, we have explored other vendors’ products. After extensive testing and discussions, we believe we can achieve even higher-quality parameters by transitioning to use of the new ELISA kits.
Testing accuracy should be about the same or perhaps better than before. However, you may note some new features associated with the reporting of results that would be good to be aware of when using these tests as part of patient care.
Reference Ranges—DSG1 and DSG3
Perhaps the most important change is the modified reference ranges, as you see here for DSG1 and DSG3 assays. While there was a category for indeterminate test results previously, results from the new test will be classified as either negative or positive. As before, results will be reported as whole integers.
Reference ranges will be viewable with the test result, and abnormal test results will be flagged in your testing software. Importantly, there is no equation or calculation that can be used to “translate” prior test results to new test results.
Results Reporting—BP180 and BP230
Reference ranges will also change for BP180 and BP230 testing.
Results Reporting: High Values
For lab testing results that exceed 200 RU/mL for any of these ELISA assays, the results will be reported as >200 RU/mL.
As is our current practice, results will be reported as round-number integers.
Summary—Changes to Expect
In summary, you will notice new reference ranges, which do not correspond quantitatively to results with prior testing kits. In addition, results exceeding 200 RU/mL will be reported as >200 RU/mL. We hope you will also experience continued high-quality testing, with enhanced testing consistency with the changes being implemented.
Please feel free to reach out to our laboratory if you have any questions about the new test or how to interpret results in a particular clinical scenario. As always, it is necessary to interpret ELISA results in each patient’s particular clinical context. We are proud of the enhancements we are making in the laboratory so as to be able to offer the highest testing quality possible for you and your patients.
If you have questions or requests relating to this talk, visit our website at mayocliniclabs.com. Thank you for watching this video.