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Updated: Jun 22, 2025
Performing and Processing FNA of Anterior Fat Pad for Amyloid
Published on: October 30, 2010
Interobserver agreement and diagnostic challenges of Congo red staining for amyloid detection on fat pad aspiration
Levent Trabzonlu1, T Leif Helland1, Melanie C Kwan1
1Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts; Harvard Medical School, Boston, Massachusetts.
Insights
Interobserver agreement for Congo red stained fat pad aspirates is low, particularly for trainees. Weak birefringence and poor stain quality present diagnostic challenges, impacting amyloid deposition evaluation.
Area of Science:
- Cytopathology
- Histopathology
- Diagnostic challenges in amyloidosis
Background:
- Congo red staining is used for amyloid deposition evaluation in fat pad aspirates.
- These specimens can be challenging for cytopathologists.
- This study aimed to assess interobserver agreement and identify variability factors.
Purpose of the Study:
- Evaluate intradepartmental interobserver agreement for Congo red stained fat pad aspirates.
- Identify factors contributing to interpretation variability.
Main Methods:
- 7 participants (3 trainees, 3 cytopathologists, 1 cytotechnologist) reviewed 50 slides each.
- Interpretations categorized as negative, indeterminate/suspicious, or positive.
- Participants reported interpretation challenges.
Main Results:
- Slight interobserver agreement overall (κ = 0.133).
- Agreement varied by group: trainees (κ = 0.028), cytopathologists (κ = 0.249).
- Weak birefringence, focal birefringence, poor stain quality, and overstaining were key challenges.
Conclusions:
- Low interobserver agreement was observed for Congo red stained fat pad aspirates.
- Weak birefringence is a significant factor causing interpretation variance.
- Standardization may be needed for consistent amyloid evaluation.
Introduction:
Congo red staining of fat pad fine needle aspiration specimens is a method utilized for evaluation of amyloid deposition. However, these specimens can pose diagnostic challenges for cytopathologists. As part of ongoing internal quality improvement measures, the objective of this study was to evaluate the intradepartmental interobserver agreement of these specimens and to identify factors that affect the variability of the interpretations.
Materials And Methods:
There were 7 participants, which included 3 trainees, 3 cytopathologists, and 1 cytotechnologist. Each participant reviewed 50 Congo red stained fat pad fine needle aspiration slides. The interpretations were categorized into 3 groups: negative, indeterminate/suspicious, and positive. The participants also noted any interpretation challenges they encountered for each case.
Results:
There was only slight interobserver agreement among all participants (κ = 0.133). Stratified by participant group, the interobserver agreement among the trainees was slight bordering on poor (κ = 0.028) and among cytopathologists was fair (κ = 0.249). The highest agreement between 2 observers was between 2 cytopathologists and the level of agreement was moderate bordering on fair (κ = 0.426). There were only 3 cases (6.0%) with full agreement among observers, while in 25 cases (50.0%), there were 2 category differences in interpretations. The primary diagnostic challenge reported by participants was when weak or focal birefringence was encountered as well as cases complicated by poor stain quality and overstaining.
Conclusions:
We found only slight interobserver agreement among all study participants. A major area of challenge was cases with weak birefringence resulting in high variance of interpretation among participants.
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