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Abstract: FR-PO744

Sensitivity and Specificity of Immunofluorescence for Diagnosing Renal Immunoglobulin-Derived Amyloidosis Compared to Mass Spectrometry

Session Information

Category: Glomerular

  • 1004 Clinical/Diagnostic Renal Pathology and Lab Medicine

Authors

  • Gonzalez Suarez, M. Lourdes, Mayo Clinic, Rochester, Minnesota, United States
  • Zhang, Pingchuan, Mayo Clinic, Rochester, Minnesota, United States
  • Nasr, Samih H., Mayo Clinic, Rochester, Minnesota, United States
  • Fidler, Mary E., Mayo Clinic, Rochester, Minnesota, United States
  • Jaffer Sathick, Insara, Mayo Clinic, Rochester, Minnesota, United States
  • Kittanamongkolchai, Wonngarm, Mayo Clinic, Rochester, Minnesota, United States
  • Kurtin, Paul J., Mayo Clinic, Rochester, Minnesota, United States
  • Leung, Nelson, Mayo Clinic, Rochester, Minnesota, United States
Background

Immunoglobulin light chain (AL) amyloidosis is the most frequent type of renal amyloidosis in the U.S., accounting for 81% of cases. Accurate typing is crucial for early diagnosis and treatment of immunoglobulin-derived (AIg)-amyloidosis (i.e. AL, AH (Ig heavy chain), AHL (Ig heavy and light chain)) and to avoid treating other types with potentially toxic chemotherapy. Immunofluorescence (IF) is the first step to type renal AIg-amyloidosis but the performance characteristics of this method are largely unknown. In this study, we aim to establish the sensitivity and specificity of IF for diagnosing AIg-amyloidosis in patients whose amyloid typing was performed by the current gold standard, laser microdissection/mass spectrometry (MS).

Methods

Renal biopsy pathology reports (2008-2015) from several institutions with diagnosis of amyloidosis by IF, which underwent a confirmatory diagnosis and typing by MS done at our center, were reviewed. Reported IF staining for kappa or lambda ≥ 2+, with weak or no staining (0, trace or 1+) for other antigens was considered positive for AL by IF.

Results

We reviewed 170 renal pathology reports. Of these, 104 cases were confirmed as AIg-amyloidosis on MS and 66 were non-AIg (including AA, ALECT2, AApo AI, AApo AII, AApo AIV, AGel, AFib) (table). IF sensitivity was 84.6%; 16 could not be diagnosed as AIg-amyloidosis by IF due to weak staining for all antigens. Lower sensitivity could be in part related to selection bias as cases with clear-cut IF findings of AL may not have undergone testing by MS. IF specificity was 92.4%; 5 cases were misdiagnosed as AIg-amyloidosis by IF.

Conclusion

In this study, IF failed to accurately differentiate AIg- from non-AIg amyloidosis in 12.3% of cases. Relying on IF alone for determining AIg vs. non-AIg amyloidosis may lead to misdiagnosis. Our data demonstrate that IF has inferior sensitivity and specificity as compared with MS in the typing of AIg-derived amyloidosis. Typing with MS is recommended in cases where IF is not certain.

Immunofluorescence results for the diagnosis of immunoglobulin- derived amyloidosis
ImmunofluorescencePositive MSNegative MSTotal of cases
Positive88593
Negative166177