Immunofluorescence on Formalin Fixed Paraffin Embedded Renal Tissue Sections: A Retrospective Study

Abstract

Introduction: Direct Immunofluorescence (DIF)/Routine Immunofluorescence (R-IF) on frozen sections is vital in the work-up of renal diseases. Sometimes, the unfixed sample may not be available for DIF or the sample may be inadequate. Paraffin Immunofluorescence (P-IF) can be used as a salvage technique in these situations. R-IF is more sensitive than P-IF in detecting Immunoglobulins (Ig) and complements. P-IF detects characteristic immunoglobulins and complements in the majority of glomerular diseases. Aim: To evaluate the sensitivity of the P-IF in comparison to the gold standard R-IF in renal biopsies with proliferative and non proliferative glomerular diseases. Materials and Methods: The present study was a retrospective study done on 52 selected cases, at St. John’s Medical College, Bangalore, Karnataka, India, data collected from January to December 2016. Based on the clinical differential diagnoses, light microscopy and R-IF findings; selected panels of immunostains (IgG, IgA, IgM, C3, C1q) were done. Proteinase K was used for enzymatic digestion. Immunofluorescence intensity was scored by two pathologists independently. Any specific pattern of staining of atleast 1+ intensity was considered as positive on P-IF. Sensitivity, specificity and confidence intervals were estimated for P-IF. Results: P-IF was done on a total of 52 selected cases. In this study P-IF showed 100% sensitivity for diagnosis of lupus nephritis, infection related glomerulonephritis, Henoch-Schönlein Purpura (HSP) nephritis and 78% for IgA nephropathy. Overall sensitivity in the diagnoses of common glomerular diseases studied was 90% (95% CI=78.97-96.80, p-value=0.025). It was less sensitive for detecting C3. Conclusion: This retrospective study demonstrated that, P-IF has a good sensitivity for diagnosing common glomerulopathies like IgA nephropathy and lupus nephritis. P-IF is a good adjunct to R-IF testing with 100% specificity.