Immunofluorescence on paraffin embedded renal biopsies: Experience of a tertiary care center with review of literature

Direct immunofluorescence on formalin-fixed, paraffin-embedded versus fresh frozen human renal biopsies: a comparative study

BACKGROUND

The data referring to the value of direct immunofluorescence on formalin-fixed, paraffin-embedded tissue (IF-Paraffin) in the diagnosis of renal diseases is controversial. The aim of this study was to investigate whether renal biopsies evaluated by routine immunofluorescence on frozen tissue (IF-Frozen) would yield adequate findings to confirm diagnoses when the IF-Paraffin technique was applied.

METHODS

To show immunoglobulins, complement components, and light chains, 55 native renal biopsies were subjected to IF-Paraffin and IF-Frozen staining techniques. The intensity of the staining was compared, and the sensitivity and specificity were calculated.

RESULTS

The IF-Paraffin technique showed a sensitivity of 89%, 81%, 86%, 30%, 71%, 60%, and 77% for IgG, IgM, IgA, C1q, C3, κ, and λ, respectively, whereas specificity was 91%, 100%, 100%, 96%, 94%, 98%, and 100%. It showed diagnostic findings in 87% of cases. Compared to cases that had both IF-Paraffin and IF-Frozen staining techniques, 43 of 55 showed either equal intensity for the diagnostic immunoglobulin/complement or a little difference.

CONCLUSIONS

Direct immunofluorescence on formalin-fixed, paraffin-embedded sections cannot replace immunofluorescence on frozen sections in the assessment of renal biopsies, but may be a "salvage technique" when frozen tissue is insufficient or unavailable and must be interpreted with great caution.

Diagnostic Utility of Direct Immunofluorescence on Paraffin-Embedded Skin Biopsy Samples for the Diagnosis of Autoimmune Vesiculobullous Lesions

Background Autoimmune vesiculobullous diseases (AIBDs) are a group of diseases characterized by blisters of the skin/mucosa due to the presence of circulating autoantibodies against antigens in the epidermis or the dermo-epidermal junction. Direct immunofluorescence (DIF) for immunoglobulin (Ig)G, IgC3, and IgA on fresh-frozen tissue is the gold standard diagnostic test for AIBDs. However, DIF in the absence of frozen tissue is challenging for the diagnosis of AIBDs. This study aimed to analyze the practical utility of DIF using paraffin-embedded skin biopsy rather than fresh frozen tissue for the diagnosis of AIBDs. Methodology This cross-sectional comparative study included 30 cases of AIBDs. DIF for IgG and IgA was performed on paraffin-embedded tissue (PE-DIF) after proteinase digestion on histopathologically confirmed 15 pemphigus vulgaris (PV), three pemphigus foliaceous (PF), four bullous pemphigoid (BP), three dermatitis herpetiformis (DH), three subcorneal pustular dermatosis (SCPD), and one case each of linear IgA disease and pemphigoid gestationis (PG). PE-DIF staining pattern was compared with the DIF on fresh frozen tissue (FF-DIF). Results All cases of PV and PF showed an intercellular IgG chicken wire staining pattern similar to FF-DIF. However, background staining was more intense in PV cases while less intense in PF cases. Three BP cases showed linear IgG staining in PE-DIF. DH, SCPD, linear IgA disease, and PG cases did not show IgG positivity. Out of three DH cases, two cases showed granular IgA positivity while linear IgA positivity along the basement membrane was seen in a single case of linear IgA disease. Negative IgG staining was observed in SCPD. Immunofluorescence in PE-DIF was rapidly deteriorating than in FF-DIF. Conclusions DIF done on paraffin-embedded tissue can be used as a supplement and salvage technique with histopathology for the diagnosis of AIBDs, particularly when a cryostat facility for frozen tissue is not available and the patient is unable to undergo a second biopsy procedure.

A Comparative Study of Immunofluorescence on Formalin-Fixed, Paraffin-Embedded Versus Fresh Frozen Kidney Biopsy

Background Immunofluorescence techniques done on formalin-fixed, paraffin-embedded tissue can serve as salvage techniques in cases where immunofluorescence on the frozen section may not be adequate or available. The present study was undertaken to assess the diagnostic utility of paraffin immunofluorescence by proteinase K digestion on renal biopsy compared to fresh frozen immunofluorescence. Methodology The paraffin immunofluorescence by proteinase K digestion of paraffin-embedded renal biopsy (IF-FFPE) was standardized and compared with the immunofluorescence on fresh frozen tissue (IF-Frozen). A total of 50 cases of the native renal biopsy were included in the study, and their intensity for fluorescein isothiocyanate-labeled IgA, IgG, IgM, C3, kappa, and lambda was compared. Results A total of 50 cases of the native renal biopsy were included in the study, and their intensity for fluorescein isothiocyanate-labeled antibodies of IgA, IgG, IgM, C3, kappa, and lambda was compared. The difference of 2+ intensity of antibodies between IF-FFPE and IF-Frozen was noted mainly in lupus nephritis (15%), followed by IgA nephropathy (10%) and membranoproliferative glomerulonephritis (7%). IF-FFPE showed a sensitivity of 90.3%, 91.8%, 82.7%, 81.1%, 92.1%, and 94.6% for IgA, IgG, IgM, C3, kappa, and lambda, respectively, whereas specificity was 100% for IgA, IgG, C3, kappa, and lambda and 95.2% for IgM. Conclusions Immunofluorescence techniques done on formalin-fixed, paraffin-embedded tissue can serve as salvage techniques in kidney biopsies.

Diagnostic Accuracy of Direct Immunofluorescence Test on Paraffin-Embedded Blocks in Comparison with Frozen Section Blocks in Renal Biopsies

Background

In several published research, the evaluation of renal disorders using immunofluorescence on formalin-fixed, paraffin-embedded (FFPE) tissue sections versus immunofluorescence on frozen sections was compared. Each technique's accuracy varies greatly. This study's objective was to assess IF-P as a potential replacement for IF-F in the diagnosis of renal biopsy specimens.

Materials and Methods

To show immunoglobulin IgA, IgG, IgM, and C3 immune deposits, proteinase K digestion of paraffin-embedded renal biopsy was standardized and used in 51 renal biopsies. Sensitivity, specificity, false-positive, and false-negative values were calculated.

Results

IF-P showed a sensitivity of 93.1%, 76.9%, 63.6%, and 33.3%, and a specificity of 100%, 97.3%, 95%, and 100% for IgG, IgA, IgM, and C3, respectively. Compared to cases that had both routine IF and IF-P, 50 of 51 showed either the same amount of staining for the diagnostic immunoglobulin/complement or a small amount of difference. In most of the cases (49 of 51), diagnostic findings were found.

Conclusion

IF-P is a sensitive and precise approach for assessing immune deposits in renal tissue biopsies. We come to the conclusion that IF-P serves as a beneficial salvage immunohistochemistry method for renal biopsies that do not contain enough cortical tissue for IF-F.

Monoclonal Gammopathy of Renal Significance: Histomorphological Spectrum at a Tertiary Care Center

Introduction

The term monoclonal gammopathy of renal significance (MGRS) has been described to include patients with renal manifestations associated with circulating monoclonal proteins with or without a clonal lymphoproliferation (B-cell or plasma cell) and not meeting diagnostic criteria for an overt hematological malignancy. A host of MGRS-associated lesions have been described that involve various renal compartments. Our study describes the histomorphological spectrum of MGRS cases at our center in the last 5 years and description as per the classification system of the International Kidney and Monoclonal Gammopathy Research Group (IKMG).

Material and Methods

Retrospective analysis was carried out of all the renal biopsies with characteristic monoclonal immunoglobulin lesions for histopathological diagnosis between years 2015 and 2020 and reviewed by two independent pathologists.

Results

Most patients in the study belonged to the fifth decade, with a median age of 50 years (mean 50.14 ± 10.43) range (24-68 years) with a male preponderance. Most patients presented with proteinuria as the sole manifestation (66.6%). Many of the patients (48%) had an M spike by serum protein electrophoresis or urinary protein electrophoresis with an abnormal serum free light chain assay (60.8%). AL amyloidosis was the most common diagnosis observed on histopathological evaluation (68.7%), followed by light chain deposition disease (10.4%).

Conclusion

MGRS lesions are infrequently encountered in the practice of nephropathology and pose a diagnostic challenge due to the limitation of a congruent clinical or hematological picture. A thorough histological examination with immunofluorescence and electron microscopy often precipitates in the right diagnosis and prompts timely management.

Spectrum of Morphological and Immunofluorescence Patterns in Lupus Nephritis: A Single Institutional Study

Introduction

Lupus nephritis (LN) is a systemic manifestation of systemic lupus erythematosus (SLE). LN commonly occurs three to five years later after the onset of SLE and is one of the leading cause of end-stage renal disease. The objective of this study was to evaluate the spectrum of morphological and immunofluorescence (IF) patterns in LN.

Methodology

A cross-sectional descriptive study was conducted on 58 renal core biopsies diagnosed as LN at Chughtai Institute of Pathology between January 2021 and December 2021. Based on the International Society of Nephrology and the Renal Pathology Society, prevalence of different classes of LN was assessed. The demographic, clinical, and biochemical parameters were analyzed in association with different histological classes of LN.

Results

In our study, the male-to-female ratio was 1:6.5. The mean age was 23.09 ± 9.23 years. Increased serum urea levels were found in 36 (62.10%) patients, and increased serum creatinine levels were found in 43 (74.12%) patients. Nephritic range proteinuria was seen in 14 (24.10%) patients, while 44 (75.90%) patients had proteinuria in the nephrotic range. Anti-double stranded DNA antibody was positive in 49 (84.50%) patients. Microscopic hematuria was present in 46 (79.30%) patients. Main bulk of patients belong to class V, 25 (43.10%), followed by class IV, 16 (27.59%). Full-house IF pattern was seen in majority of patients.

Conclusion

This study showed a high frequency of prevalence of advanced classes of LN, i.e., class V followed by class IV. There is a strong diagnostic utility of IF in LN. Similarly, full-house IF pattern was observed in majority of patients in our study, irrespective of which class of LN they belonged to.

Fluorescent Immunohistochemistry

Immunofluorescence is an important immunochemical technique that utilizes fluorescence-labeled antibodies to detect specific target antigens. It is used widely in both scientific research and clinical laboratories. Immunofluorescence allows for excellent sensitivity and amplification of signal in comparison to immunohistochemistry. However, analysis of samples labeled with fluorescence-labeled antibodies has to be performed using a fluorescence microscope or other type of fluorescence imaging. There are two methods available: direct (primary) and indirect (secondary) immunofluorescence. Here, we describe the principle of immunofluorescence methods as well as the preparation of fresh-frozen and formalin-fixed, paraffin embedded tissues for both direct and indirect immunofluorescence labeling.

KM55 in the Evaluation of IgA-Containing Glomerular Diseases

Introduction

Mucosal-derived galactose-deficient IgA is central to the pathogenesis of primary IgA nephropathy (IgAN). Recent reports suggest similar pathogenesis in Henoch-Schonlein purpura (HSP) and secondary IgAN. Its role in other IgA-containing glomerular diseases is still under investigation. It can be detected in glomeruli with the recently described antibody KM55. We aimed to evaluate the role of KM55 by immunostaining a wide spectrum of IgA-containing glomerular diseases.

Methods

After standardization and colocalization in a case of IgAN, a spectrum of 60 cases including IgAN, HSP, chronic liver disease (CLD)-related IgAN, other secondary IgAN, IgA-dominant/codominant membranoproliferative glomerulonephritis (MPGN), and lupus nephritis were subjected to immunofluorescence with KM55. KM55 was used to resolve diagnostic dilemma in cases of IgA deposition with confounding histology.

Results

The group of primary IgAN (17 cases), HSP (4 cases), and secondary IgAN (19 cases) including CLD showed 2-3+ granular staining with KM55, suggesting mucosal-derived IgA. In contrast, cases of IgA-dominant/codominant MPGN (8 cases) and lupus nephritis (12 cases) were negative for KM55, suggesting systemic derivation of IgA. In cases of IgA deposition with confounding histology such as membranoproliferative or diffuse endocapillary proliferative pattern, KM55 helped to resolve the diagnosis.

Discussion/Conclusion

This cross-sectional study concludes that KM55 is useful in the evaluation of IgA-containing glomerular diseases from a pathogenetic perspective and is a practical tool in resolving differential diagnosis in cases with overlapping histopathological features.

Pitfalls and Caveats in Applying Chromogenic Immunostaining to Histopathological Diagnosis

Chromogenic immunohistochemistry (immunostaining using an enzyme-labeled probe) is an essential histochemical technique for analyzing pathogenesis and making a histopathological diagnosis in routine pathology services. In neoplastic lesions, immunohistochemistry allows the study of specific clinical and biological features such as histogenesis, behavioral characteristics, therapeutic targets, and prognostic biomarkers. The needs for appropriate and reproducible methods of immunostaining are prompted by technical development and refinement, commercial availability of a variety of antibodies, advanced applicability of immunohistochemical markers, accelerated analysis of clinicopathological correlations, progress in molecular targeted therapy, and the expectation of advanced histopathological diagnosis. However, immunostaining does have various pitfalls and caveats. Pathologists should learn from previous mistakes and failures and from results indicating false positivity and false negativity. The present review article describes various devices, technical hints, and trouble-shooting guides to keep in mind when performing immunostaining.

Paraffin Immunofluorescence Increases Light-Chain Detection in Extra-Renal Light Chain Amyloidosis and Other Light-Chain-Associated Diseases

CONTEXT.—

Distinguishing the different types of amyloid is clinically important because treatments and outcomes are different. Mass spectrometry is the new gold standard for amyloid typing, but it is costly and not widely available. Therefore, immunolabeling remains the first step in identifying the most common types of amyloidosis. In amyloid subtyping, direct immunofluorescence works well when applied to frozen sections, but immunohistochemistry on formalin-fixed, paraffin-embedded material often yields poor results, particularly for light chain amyloidosis. Recently, paraffin immunofluorescence has been described as a valuable salvage technique in renal pathology when frozen sections are not available but it has not been evaluated for extra-renal diseases.

OBJECTIVES.—

To evaluate the use of paraffin immunofluorescence for light-chain detection in extra-renal amyloidosis and other light-chain-associated diseases.

DESIGN.—

First, we compared the staining intensity of both light chains between paraffin immunofluorescence and immunohistochemistry on a retrospective cohort of 28 cases of amyloidosis that have been previously typed. Then, we studied the role of paraffin immunofluorescence as an addition to our classical immunohistochemistry panel for amyloidosis typing.

RESULTS.—

In the retrospective cohort, we found that paraffin immunofluorescence outperformed immunohistochemistry for light-chain detection. Then, in the prospective part of the study, we showed that the proportion of correctly classified cases increased from 50% to 71.9% with the adjunction of second-intention paraffin immunofluorescence to the immunohistochemistry procedure.

CONCLUSIONS.—

We therefore view paraffin immunofluorescence as a significant addition to the routine workflow for detection of light-chain-related diseases.

Deep learning for the classification of medical kidney disease: a pilot study for electron microscopy

Artificial intelligence (AI) is a new frontier and often enigmatic for medical professionals. Cloud computing could open up the field of computer vision to a wider medical audience and deep learning on the cloud allows one to design, develop, train and deploy applications with ease. In the field of histopathology, the implementation of various applications in AI has been successful for whole slide images rich in biological diversity. However, the analysis of other tissue medias, including electron microscopy, is yet to be explored. The present study aims to evaluate deep learning for the classification of medical kidney disease on electron microscopy images: amyloidosis, diabetic glomerulosclerosis, membranous nephropathy, membranoproliferative glomerulonephritis (MPGN), and thin basement membrane disease (TBMD). We found good overall classification with the MedKidneyEM-v1 Classifier and when looking at normal and diseased kidneys, the average area under the curve for precision and recall was 0.841. The average area under the curve for precision and recall on the disease only cohort was 0.909. Digital pathology will shape a new era for medical kidney disease and the present study demonstrates the feasibility of deep learning for electron microscopy. Future approaches could be used by renal pathologists to improve diagnostic concordance, determine therapeutic strategies, and optimize patient outcomes in a true clinical environment.

Clinical correlation and prognostic significance of immunofluorescence in renal biopsies of patients having Glomerulonephritis

Objective

To correlate the immunofluorescence (IF) findings on renal biopsies of patients of glomerulonephritis (GN) with the clinical course of the disease.

Methods

This retrospective descriptive study was done at the Department of Pediatrics Medicine Unit-I, Nishtar Hospital Multan, from January 2008 to January 2019. A total of 387 cases of both gender, aged up to 16 years, diagnosed having GN on the basis of renal biopsies by light microscopy (LM) and IF findings, were included. Outcome as remission, partial remission, no remission with stable kidney disease, no remission with progressive kidney disease and end-stage kidney disease (ESKD) were computed. Chi square test was applied to see the correlation of IF findings and outcome by taking p value less than 0.05 as statistically significant.

Results

Focal segmental glomerulosclerosis (FSGS) was found to be the commonest histopathology finding noted in 158 (40.8%) followed by mesangioproliferative GN 74 (19.1%) and membranous nephropathy 42 (10.9%). Complete remission was observed in 145 (37.5%) cases whereas ESKD was seen in 26 (6.7%). Distinct pattern of IF findings were shown when distribution of IF findings were seen with respect to all study variables (p value < 0.001). For outcome, 134 (51.3%) IF negative cases had complete remission while 93 (35.6%) negative IF findings also had partial remission. ESKD was seen among 14 (25.9%) IgM positive and three (33.3%) IgA positive cases.

Conclusion

Immunofluorescence proved an important diagnostic tool in reaching the exact diagnosis in various types of GN. Distinct correlation between IF findings and clinical course of various types of GN was observed. IF negative cases had better outcome and was not having progressive course of disease so prognosis remained better than IF positive cases in this study.

Validation of phospholipase A2 receptor direct immunofluorescence staining in the diagnosis of primary membranous glomerulonephritis

Distinguishing between primary and secondary subtypes of membranous glomerulonephritis (MGN) is critical for its clinical management. We prospectively compared direct immunofluorescence (DIF) staining for phospholipase A₂ receptor (PLA₂R) on frozen renal biopsy with the presence of detectable serum PLA₂R antibody assessed by enzyme linked immunosorbent assay (ELISA) in the diagnosis of primary MGN. Forty-six patients with biopsy-proven MGN were enrolled from April 2017 to June 2019 with 31/46 (67.4%) being primary and 15/46 (32.6%) being secondary as determined by comprehensive clinical assessment. This is currently deemed to be the gold standard for distinguishing primary from secondary MGN. Amongst the 31 primary MGN patients, 24/31 were positive on PLA₂R DIF staining compared to 18/31 being positive on the PLA₂R ELISA (p=0.03). Amongst the 15 secondary MGN patients, 1/15 was positive on PLA₂R DIF compared to 0/15 on PLA₂R ELISA (p=1.0). In conclusion, the presence of PLA₂R staining on DIF demonstrated superior sensitivity and similar specificity compared to the detection of circulating PLA₂R antibodies by ELISA in the diagnosis of primary MGN in a cohort of 46 patients with biopsy-proven MGN. We suggest that DIF should be considered as part of routine work-up in all newly diagnosed cases of MGN.

Immunoperoxidase and Immunofluorescence on Formalin-Fixed, Paraffin-Embedded Tissue Sections versus Immunofluorescence on Frozen Sections in the Assessment of Renal Biopsies

Introduction:

There are few published studies comparing immunofluorescence on formalin-fixed, paraffin-embedded (FFPE) tissue sections (IF-P) and immunoperoxidase on FFPE tissue sections (IP-P) with immunofluorescence on frozen sections (IF-F) for evaluation of renal diseases. Also, the accuracy for each method differs greatly. The aim of this study was to evaluate IF-P and IP-P as an alternative to IF-F (gold standard method) in the diagnosis of renal biopsies specimens.

Methods:

In all, 101 renal biopsies were subjected to IF-P, IP-P, and IF-F staining to demonstrate immunoglobulin IgA, IgG, and IgM immune deposits. Sensitivity, specificity, false-positive, and false-negative values were calculated.

Results:

IP-P showed sensitivity of 61.8%, 74.2%, and 64.2%, and specificity of 84.8%, 69.2%, and 66.7% for IgA, IgG, and IgM, respectively. IF-P showed a sensitivity of 45.6%, 69.4% and 52.8%, and specificity of 87.9%, 87.2% and 77.1% for IgA, IgG and IgM, respectively. False-positive cases of IF-P and IP-P were 4, 5, and 11 and 5, 12, and 16 for IgA, IgG, and IgM, respectively.

Conclusion:

Where IF-F lacks glomeruli or fresh renal biopsies are not available, IP-P is a sensitive method, whereas IF-P is a specific method for the evaluation of immune deposits in the renal tissue biopsies. The presence of false-positive cases in both methods deserves further research.

A case of lupus vasculopathy presenting favorable renal outcome

Noninflammatory necrotizing vasculopathy, also referred to as lupus vasculopathy, is not infrequently observed in the pathology of lupus nephritis. It affects vessels causing them to become severely narrowed and occluded by a mechanism involving immune complexes. We experienced a 51-year-old woman with lupus nephritis class IV + V, which was accompanied by lupus vasculopathy. Renal biopsy and light microscopy showed eosinophilic hyaline-like material in the afferent and/or efferent arterioles, which narrowed the lumen, and which were positive for IgG by immunofluorescent analysis. Electron microscopy indicated that amorphous material and endothelial detachment occluded the arterioles. These findings were consistent with those of lupus vasculopathy. We treated the patient with steroids and cyclophosphamide. By the day of discharge, her levels of creatinine and proteinuria had undergone partial remission. Although lupus vasculopathy was implied as a lesion with unfavorable renal prognosis, some recent reports suggest its true renal prognosis is not unfavorable necessarily. Nevertheless, lupus vasculopathy is an important finding in diagnosis in contradiction to other vascular legions in systemic lupus erythematosus. In addition, a standard therapy has also not been established. Therefore, it is important to accumulate cases of lupus vasculopathy to determine its prognosis and develop standard treatments.

Monoclonal gammopathy of renal significance: clinical manifestation, pathogenic characteristic and treatment

Monoclonal gammopathy of renal significance (MGRS) is a group of renal disorders caused by a monoclonal immunoglobulin (MIg) secreted by a dangerous plasmatic/B-cell clone hyperplasia through MIg deposition or dysfunction of complement pathway, with increasing risk of progress to end stage renal disease (ESRD) and the underlying hematologic malignancy. The combination of renal biopsy, complete laboratory examination and bone marrow biopsy is an indispensable diagnostic tool for MGRS to identify accurately and unequivocally the pathogenic monoclonal MIg and provide guidance to treatment. Treatment of MGRS is composed of conventional therapy, chemotherapy, and stem cell transplantation to target the underlying clone and eliminate the noxious MIg on the basis of clinical data of some retrospective studies and a small amount of prospective trial. In addition, it is worthwhile point out assessment of therapeutic effect is significantly relevant for renal and overall prognosis. Thus, by comprehensively analyzing the clinical manifestations and pathogenic characteristic of MGRS, early recognition and prompt treatment can improve the prognosis and prevent post-translation recurrence with multidisciplinary cooperation.

Glomerular C4d Staining Does Not Exclude a C3 Glomerulopathy

Introduction

C4d, an early product in the classical/lectin complement pathway has shown potential in the evaluation of C3 glomerulopathy where its absence would support an alternative pathway abnormality. As autoimmune/genetic complement testing is not readily available to most parts of the world, glomerular C4d staining may serve as a useful additional step toward the diagnosis.

Methods

To test this hypothesis, C4d staining was performed on a large cohort of C3 glomerulopathy. Archival cases from 2011 to 2017 were reviewed and immunohistochemistry for C4d was performed, scored (scale of 0 to 3+), and correlated with the immunofluorescence and ultrastructural findings. Paraffin immunofluorescence was performed in cases of "discordant C4d" to unmask Igs.

Results

Twenty-seven cases of dense deposit disease (DDD) and 14 cases of C3 glomerulonephritis (C3GN) were retrieved. C4d demonstrated a range of staining intensities with negative/traces in only 22% of DDD and 64% of C3GN. Lower-intensity C4d staining (1 to 2+) was mostly concordant with similar amounts of Igs/C1q. Discordant 3+ staining was noted in approximately 50% of cases of DDD and 20% of cases of C3GN. Among them, paraffin immunofluorescence unmasked polyclonal Igs in 2 of 5 cases of DDD and 1 of 3 cases of C3GN.

Conclusion

This observational study suggests that the presence of glomerular C4d should not exclude a C3 glomerulopathy. In lower intensities, it appears to represent overlying classical/lectin pathway activation with concordant Ig/C1q deposits. A subset of cases, however, displays intense and discordant C4d staining, which raises the possibility of an associated lectin pathway abnormality, a potential future area of study.

Paraffin Immunofluorescence: A Role Beyond Kidney Biopsies

Paraffin immunofluorescence is a well established "salvage" technique in renal pathology when representative glomeruli are not found in the fresh frozen tissue sent for routine direct immunofluorescence studies. A step of enzymatic digestion of the formalin-fixed paraffin-embedded biopsy exposes the antigenic immune complexes and allows staining with fluorochrome-tagged antibodies. We explored the utility of the technique of paraffin immunofluorescence outside the kidney in certain specific scenarios including extra renal amyloid and duodenal macroglobulinemia.

Paraffin Immunofluorescence: A Valuable Ancillary Technique in Renal Pathology

Immunofluorescence on frozen tissue is the gold standard immunohistochemical technique for evaluation of immune deposits in the kidney. When frozen tissue is not available or lacks glomeruli, immunofluorescence can be performed on paraffin tissue after antigen retrieval (paraffin immunofluorescence). Excellent results can be obtained by paraffin immunofluorescence in most immune complex-mediated glomerulonephritides and dysproteinemia-associated kidney lesions, and thus this technique has become a valuable salvage technique in renal pathology. Furthermore, new data have emerged suggesting that paraffin immunofluorescence can be used as an unmasking technique, as it is more sensitive than frozen tissue immunofluorescence in some kidney lesions, such as crystalline light chain proximal tubulopathy and is needed to establish the diagnosis of certain unique lesions, such as membranous-like glomerulopathy with masked IgG kappa deposits and membranoproliferative glomerulonephritis with masked monotypic Ig deposits. However, it is important to recognize and be aware of the limitations and pitfalls associated with paraffin immunofluorescence. These include poor sensitivity for detection of C3 deposits and for the diagnosis of primary membranous nephropathy. Here, we summarize the available techniques of paraffin immunofluorescence, review its role and performance as a salvage and unmasking technique in renal pathology, address its limitations and pitfalls, and highlight unusual forms of glomerulopathy that require paraffin immunofluorescence for diagnosis.