Non-myeloma light chain cast nephropathy: a multicenter retrospective study on clinicopathological characteristics.

Not available.

A Prospective Study on Complement Activation Distinguishes Focal Segmental Glomerulosclerosis from Minimal Change Disease.

Introduction: Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are related podocytopathies with distinct kidney outcomes. Surprisingly, elevated urinary activation fragments have been found in FSGS despite little complement deposition on immunofluorescence (IF) staining. Whether complement activation distinguishes FSGS from MCD, participating in the development of segmental lesions, remains unknown. Methods: We performed an observational study in patients with MCD and FSGS, and proteinuria ≥1 g/g of creatinine. We included both primary and secondary or unknown causes. We compared urinary fragments of terminal pathway activation, sC5b9, and C5a expressed as creatinine ratios, between MCD and FSGS. Results: Patients with FSGS (n = 41) had a serum albumin of 31±10 g/l and proteinuria of 5.1 (2.6-9.1) g/g at sampling, whereas those with MCD (n = 15) had a lower serum albumin (22 ± 9 g/l; P = 0.002), and a proteinuria of 3.8 (1.9-7.7) g/g (P = 0.40). Urinary sC5b9 and C5a were 8.7 (1.7-52.3) and 1.26 (0.45-1.84) µg/mmol of creatinine, respectively in patients with FSGS; compared to 0.8 (0.0-1.5) and 0.06 (0.01-0.15) µg/mmol of creatinine in MCD (P < 0.001), respectively. We found no association between urinary complement fragments and age, estimated glomerular filtration rate (eGFR), or chronic kidney lesions. When analyzing samples with proteinuria ≥ 3 g/g, the c-statistics for urinary sC5b9 and C5a were 0.96 and 1.00, respectively, in differentiating FSGS from MCD. Conclusion: We found no urinary complement activation fragments in MCD, in comparison to FSGS, despite similar levels of proteinuria. This suggests a role for complement activation in the pathogenesis of FSGS and provides an additional tool for distinguishing these 2 entities.

Atypical Anti-Glomerular Basement Membrane Nephritis: A Case Series From the French Nephropathology Group.

RATIONALE & OBJECTIVE: Atypical anti-glomerular basement membrane (GBM) nephritis is characterized by a bright linear immunoglobulin staining along the GBM by immunofluorescence without a diffuse crescentic glomerulonephritis nor serum anti-GBM antibodies by conventional enzyme-linked immunosorbent assay (ELISA). We characterized a series of patients with atypical anti-GBM disease. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: Patients identified by the French Nephropathology Group as having atypical anti-GBM nephritis between 2003 and 2022. FINDINGS: Among 38 potential cases, 25 were included, of whom 14 (56%) were female and 23 (92%) had hematuria. The median serum creatinine at diagnosis was 150 (IQR, 102-203) µmol/L and median urine protein-creatinine ratio (UPCR) was 2.4 (IQR, 1.3-5.2) g/g. Nine patients (36%) had endocapillary proliferative glomerulonephritis (GN), 4 (16%) had mesangial proliferative GN, 4 (16%) had membranoproliferative GN, 2 (8%) had pure and focal crescentic GN, 1 (4%) had focal segmental glomerulosclerosis, and 5 had glomeruli that were unremarkable on histopathology. Nine patients (36%) had crescents, involving a median of 9% of glomeruli. Bright linear staining for IgG was seen in 22 cases (88%) and for IgA in 3 cases (12%). The 9 patients (38%) who had a monotypic staining pattern tended to be older with less proteinuria and rarely had crescents. Kidney survival rate at 1 year was 83% and did not appear to be associated with the light chain restriction. LIMITATIONS: Retrospective case series with a limited number of biopsies including electron microscopy. CONCLUSIONS: Compared with typical anti-GBM disease, atypical anti-GBM nephritis frequently presents with an endocapillary or mesangial proliferative glomerulonephritis pattern and appears to have a slower disease progression. Further studies are needed to fully characterize its pathophysiology and associated clinical outcomes. PLAIN-LANGUAGE SUMMARY: Atypical anti-glomerular basement membrane (GBM) nephritis is characterized histologically by bright linear immunoglobulin staining along the GBM without diffuse crescentic glomerulonephritis or circulating anti-GBM antibodies. We report a case series of 25 atypical cases of anti-GBM nephritis in collaboration with the French Nephropathology Group. Compared with typical anti-GBM disease, we observed a slower disease progression. Patients frequently presented with heavy proteinuria and commonly had evidence of endocapillary or mesangial proliferative glomerulonephritis. About half of the patients displayed a monotypic immune staining pattern; they tended to be older, with less proteinuria, and commonly without glomerular crescents in biopsy specimens. No concomitant circulating monoclonal gammopathy was detected. Further studies are needed to fully characterize its pathophysiology and associated clinical outcomes.

The Banff 2022 Kidney Meeting Work Plan: Data-driven refinement of the Banff Classification for renal allografts.

The XVIth Banff Meeting for Allograft Pathology was held in Banff, Alberta, Canada, from September 19 to 23, 2022, as a joint meeting with the Canadian Society of Transplantation. In addition to a key focus on the impact of microvascular inflammation and biopsy-based transcript analysis on the Banff Classification, further sessions were devoted to other aspects of kidney transplant pathology, in particular T cell-mediated rejection, activity and chronicity indices, digital pathology, xenotransplantation, clinical trials, and surrogate endpoints. Although the output of these sessions has not led to any changes in the classification, the key role of Banff Working Groups in phrasing unanswered questions, and coordinating and disseminating results of investigations addressing these unanswered questions was emphasized. This paper summarizes the key Banff Meeting 2022 sessions not covered in the Banff Kidney Meeting 2022 Report paper and also provides an update on other Banff Working Group activities relevant to kidney allografts.

Corrigendum: Delphi: A Democratic and Cost-Effective Method of Consensus Generation in Transplantation.

[This corrects the article DOI: 10.3389/ti.2023.11589.].

Corrigendum: Thrombotic Microangiopathy in the Renal Allograft: Results of the TMA Banff Working Group Consensus on Pathologic Diagnostic Criteria.

[This corrects the article DOI: 10.3389/ti.2023.11590.].

Cure Glomerulonephropathy Pathology Classification and Core Scoring Criteria, Reproducibility, and Clinicopathologic Correlations.

Introduction: Cure Glomerulonephropathy (CureGN) is an observational cohort study of patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), or IgA nephropathy. We developed a conventional, consensus-based scoring system to document pathologic features for application across multiple pathologists and herein describe the protocol, reproducibility, and correlation with clinical parameters at biopsy. Methods: Definitions were established for glomerular, tubular, interstitial, and vascular lesions evaluated semiquantitatively using digitized light microscopy slides and electron micrographs, and reported immunofluorescence. Cases with curated pathology materials as of April 2019 were scored by a randomly assigned pathologist, with at least 10% of cases scored by a second pathologist. Scoring reproducibility was assessed using Gwet's agreement coefficient (AC)1 statistic and correlations with clinical variables were performed. Results: Of 800 scored biopsies (134 MCD, 194 FSGS, 206 MN, 266 IgA), 94 were scored twice (11.8%). Of 60 pathology features, 46 (76.7%) demonstrated excellent (AC1>0.8), and 12 (20.0%) had good (AC1 0.6-0.8) reproducibility. Mesangial hypercellularity scored as absent, focal, or diffuse had moderate reproducibility (AC1 = 0.58), but good reproducibility (AC1 = 0.71) when scored as absent or focal versus diffuse. The percent glomeruli scored as no lesions had fair reproducibility (AC1 = 0.34). Strongest correlations between pathologic features and clinical characteristics at biopsy included interstitial inflammation, interstitial fibrosis, and tubular atrophy with estimated glomerular filtration rate, foot process effacement with urine protein/creatinine ratio, and active crescents with hematuria. Conclusions: Most scored pathology features showed excellent reproducibility, demonstrating consistency for these features across multiple pathologists. Correlations between certain pathologic features and expected clinical characteristics show the value of this approach for future studies on clinicopathologic correlations and biomarker discovery.

Delphi: A Democratic and Cost-Effective Method of Consensus Generation in Transplantation.

The Thrombotic Microangiopathy Banff Working Group (TMA-BWG) was formed in 2015 to survey current practices and develop minimum diagnostic criteria (MDC) for renal transplant TMA (Tx-TMA). To generate consensus among pathologists and nephrologists, the TMA BWG designed a 3-Phase study. Phase I of the study is presented here. Using the Delphi methodology, 23 panelists with >3 years of diagnostic experience with Tx-TMA pathology listed their MDC suggesting light, immunofluorescence, and electron microscopy lesions, clinical and laboratory information, and differential diagnoses. Nine rounds (R) of consensus resulted in MDC validated during two Rs using online evaluation of whole slide digital images of 37 biopsies (28 TMA, 9 non-TMA). Starting with 338 criteria the process resulted in 24 criteria and 8 differential diagnoses including 18 pathologic, 2 clinical, and 4 laboratory criteria. Results show that 3/4 of the panelists agreed on the diagnosis of 3/4 of cases. The process also allowed definition refinement for 4 light and 4 electron microscopy lesions. For the first time in Banff classification, the Delphi methodology was used to generate consensus. The study shows that Delphi is a democratic and cost-effective method allowing rapid consensus generation among numerous physicians dealing with large number of criteria in transplantation.

Thrombotic Microangiopathy in the Renal Allograft: Results of the TMA Banff Working Group Consensus on Pathologic Diagnostic Criteria.

The Banff community summoned the TMA Banff Working Group to develop minimum diagnostic criteria (MDC) and recommendations for renal transplant TMA (Tx-TMA) diagnosis, which currently lacks standardized criteria. Using the Delphi method for consensus generation, 23 nephropathologists (panelists) with >3 years of diagnostic experience with Tx-TMA were asked to list light, immunofluorescence, and electron microscopic, clinical and laboratory criteria and differential diagnoses for Tx-TMA. Delphi was modified to include 2 validations rounds with histological evaluation of whole slide images of 37 transplant biopsies (28 TMA and 9 non-TMA). Starting with 338 criteria in R1, MDC were narrowed down to 24 in R8 generating 18 pathological, 2 clinical, 4 laboratory criteria, and 8 differential diagnoses. The panelists reached a good level of agreement (70%) on 76% of the validated cases. For the first time in Banff classification, Delphi was used to reach consensus on MDC for Tx-TMA. Phase I of the study (pathology phase) will be used as a model for Phase II (nephrology phase) for consensus regarding clinical and laboratory criteria. Eventually in Phase III (consensus of the consensus groups) and the final MDC for Tx-TMA will be reported to the transplantation community.

Kidney Biopsy Findings Among Allogenic Hematopoietic Stem Cell Transplant Recipients With Kidney Injury: A Case Series.

Rationale and Objective: The incidence of kidney disease is high in patients after allogeneic hematopoietic cell transplantation (aHCT). Although rarely performed, kidney biopsy may be useful to make a precise diagnosis because several mechanisms and risk factors can be involved, and to adjust the treatment accordingly. This case series aimed to report the spectrum of biopsy findings from patients with kidney injury after aHCT. Study Design: Single-center retrospective case series. Setting and Participants: All individuals who underwent a native kidney biopsy, among all adult patients who received aHCT in a tertiary hospital in Montreal (Canada) from January 1, 2010, to December 31, 2020, were identified, and the clinical data were extracted from their medical records. Results: A total of 17 patients were included. Indications for biopsy included acute kidney injury (n=6), chronic kidney disease (n=5), nephrotic syndrome (n=4), and subnephrotic proteinuria (n=2). Pathologic findings from the kidney biopsy were heterogenous: 10 patients showed evidence of thrombotic microangiopathy (TMA), 5 of acute tubular injury, and 4 of membranous nephropathy. Cases of acute interstitial nephritis, BK virus nephropathy, immune complex nephropathy, focal and segmental glomerulosclerosis, minimal change disease, and karyomegalic-like interstitial nephritis were also described. Limitations: There was no systematic kidney biopsy performed for all patients with kidney injury after aHCT. Only a small proportion of patients with kidney damage underwent biopsy, making the results less generalizable. Conclusions: Kidney biopsy is useful in patients with kidney disease after aHCT to make a precise diagnosis and tailor therapy accordingly. This series is one of the few published studies describing pathologic findings of biopsies performed after aHCT in the context of acute kidney injury and chronic kidney disease. TMA was widely present on biopsy even when there was no clinical suspicion of such a diagnosis, suggesting that the current clinical criteria for a diagnosis of TMA are not sensitive enough for kidney-limited TMA.

NEF-Induced HIV-Associated Nephropathy Through HCK/LYN Tyrosine Kinases.

HIV-1-associated nephropathy (HIVAN) is a severe complication of HIV-1 infection. To gain insight into the pathogenesis of kidney disease in the setting of HIV, a transgenic (Tg) mouse model [CD4C/HIV-negative regulator factor (Nef)] was used in which HIV-1 nef expression is under control of regulatory sequences (CD4C) of the human CD4 gene, thus allowing expression in target cells of the virus. These Tg mice develop a collapsing focal segmental glomerulosclerosis associated with microcystic dilatation, similar to human HIVAN. To identify kidney cells permissive to the CD4C promoter, CD4C reporter Tg lines were used. They showed preferential expression in glomeruli, mainly in mesangial cells. Breeding CD4C/HIV Tg mice on 10 different mouse backgrounds showed that HIVAN was modulated by host genetic factors. Studies of gene-deficient Tg mice revealed that the presence of B and T cells and that of several genes was dispensable for the development of HIVAN: those involved in apoptosis (Trp53, Tnfsf10, Tnf, Tnfrsf1b, and Bax), in immune cell recruitment (Ccl3, Ccl2, Ccr2, Ccr5, and Cx3cr1), in nitric oxide (NO) formation (Nos3 and Nos2), or in cell signaling (Fyn, Lck, and Hck/Fgr). However, deletion of Src partially and that of Hck/Lyn largely abrogated its development. These data suggest that Nef expression in mesangial cells through hematopoietic cell kinase (Hck)/Lck/Yes novel tyrosine kinase (Lyn) represents important cellular and molecular events for the development of HIVAN in these Tg mice.

Rapid Progression of Focal Segmental Glomerulosclerosis in Patients with High-Risk APOL1 Genotypes.

BACKGROUND: FSGS is a heterogeneous diagnosis with a guarded prognosis. Polymorphisms in the apolipoprotein L1 ( APOL1 ) gene are associated with developing FSGS and faster progression to kidney failure in affected patients. Better understanding the natural history of patients with FSGS and APOL1 risk alleles is essential to improve patient care and support the design and interpretation of interventional studies. The objective of this study was to evaluate the quantitative association between APOL1 and kidney disease progression and the interaction with other clinical and laboratory factors. METHODS: CureGN cohort study participants with biopsy diagnosis of FSGS, regardless of self-identified race, were included. The exposure of interest was two APOL1 risk alleles (high risk) versus zero to one risk alleles (low risk). The primary outcome was eGFR slope categorized as rapid progressor (eGFR slope ≤-5 ml/min per year), intermediate progressor (slope between 0 and -5), or nonprogressor (slope ≥0). Multivariable ordinal logistic and linear regressions were used for adjusted analyses. Missing data were addressed using multiple imputation. RESULTS: Of 650 participants, 476 (73%) had genetic testing, among whom 87 (18%) were high risk. High-risk participants were more likely to have lower median eGFR (62 [interquartile range, 36-81] versus low-risk participants 76 ml/min per 1.73 m 2 [interquartile range, 44-106]; P <0.01). In adjusted analysis, the odds of more rapid progression of eGFR was 2.75 times higher (95% confidence interval, 1.67 to 4.53; P <0.001) in the high-risk versus low-risk groups. CONCLUSIONS: In patients with FSGS, high-risk APOL1 genotype is the predominant factor associated with more rapid loss of kidney function.

A Comprehensive Multidisciplinary Diagnostic Algorithm for the Early and Efficient Detection of Amyloidosis.

Amyloidosis is a rare protein misfolding disease caused by the accumulation of amyloid fibrils in various tissues and organs. There are different subtypes of amyloidosis, with light chain (AL) amyloidosis being the most common. Amyloidosis is notoriously difficult to diagnose because it is clinically heterogeneous, no single test is diagnostic for the disease, and diagnosis typically involves multiple specialists. Here, we propose an integrated, multidisciplinary algorithm for efficiently diagnosing amyloidosis. Drawing on research from several medical disciplines, we have combined clinical decisions and best practices into a comprehensive algorithm to facilitate the early detection of amyloidosis. Currently, many patients are diagnosed more than 6 months after symptom onset, yet early diagnosis is the major predictor of survival. Our algorithm aims to shorten the time to diagnosis with efficient sequencing of tests and minimizing uninformative investigations. We also recommend typing and staging of confirmed amyloidosis to guide treatment. By reducing time to diagnosis, our algorithm could lead to earlier and more targeted treatment, ultimately improving prognosis and survival.

Renal AA amyloidosis: presentation, diagnosis, and current therapeutic options: a review.

Amyloid A amyloidosis is thought to be the second most common form of systemic amyloidosis behind amyloidosis secondary to monoclonal Ig. It is the result of deposition of insoluble fibrils in the extracellular space of tissues and organs derived from the precursor protein serum amyloid A, an acute phase reactant synthesized excessively in the setting of chronic inflammation. The kidney is the most frequent organ involved. Most patients present with proteinuria and kidney failure. The diagnosis is made through tissue biopsy with involvement of the glomeruli in most cases, but also often of the vessels and the tubulointerstitial compartment. The treatment usually targets the underlying etiology and consists increasingly of blocking the inflammatory cascade of cytokines with interleukin-1 inhibitors, interleukin-6 inhibitors, and tumor necrosis factor-α inhibitors to reduce serum amyloid A protein formation. This strategy has also shown efficacy in cases where an underlying etiology cannot be readily identified and has significantly improved the prognosis of this entity. In addition, there has been increased interest at developing effective therapies able to clear amyloid deposits from tissues, albeit with mitigated results so far.

Clinicopathologic Significance of Predominant Lambda Light Chain Deposition in IgA Nephropathy.

Introduction: IgA nephropathy (IgAN) differs from other glomerular diseases by the frequently predominant lambda over kappa light chain deposition. Using the Cure Glomerulonephropathy (CureGN) IgAN cohort, we aimed to determine whether predominant lambda chain deposition is associated with worse clinical outcomes or histopathologic markers of more active disease. Methods: Patients were categorized based on the intensity of light chain staining. The lambda dominant (LD) group was defined by a difference in intensity score of lambda minus kappa ≥ 1+ and the kappa-lambda codominant (KL) group by a difference < 1+. We compared the clinical course of patients in each category from the time of kidney biopsy and time of enrollment into CureGN to the time of remission (proteinuria < 0.3 g/g), 50% reduction in estimated glomerular filtration rate (eGFR), or progression to end-stage kidney disease (ESKD). We also analyzed differences in histopathologic characteristics between the 2 groups. Results: Among 440 patients, we found no significant differences between groups in baseline clinical characteristics nor in rates of remission, 50% reduction in eGFR, or progression to ESKD. Patients in the LD group had a modestly greater frequency of IgG staining ≥ 1+. The biopsy results of 234 patients reviewed by CureGN pathologists revealed a greater frequency of endocapillary hypercellularity (51.1% vs. 36.3%, P = 0.04) in the LD group, but no other significant difference in histopathologic features. Conclusion: In IgAN, we found an association between lambda predominance and increased endocapillary hypercellularity, but no association with clinical outcomes.

SMOC2 promotes an epithelial-mesenchymal transition and a pro-metastatic phenotype in epithelial cells of renal cell carcinoma origin.

Renal Cell Carcinoma (RCC) is the most common form of all renal cancer cases, and well-known for its highly aggressive metastatic behavior. SMOC2 is a recently described non-structural component of the extracellular matrix (ECM) that is highly expressed during tissue remodeling processes with emerging roles in cancers, yet its role in RCC remains elusive. Using gene expression profiles from patient samples, we identified SMOC2 as being significantly expressed in RCC tissue compared to normal renal tissue, which correlated with shorter RCC patient survival. Specifically, de novo protein synthesis of SMOC2 was shown to be much higher in the tubular epithelial cells of patients with biopsy-proven RCC. More importantly, we provide evidence of SMOC2 triggering kidney epithelial cells into an epithelial-to-mesenchymal transition (EMT), a phenotype known to promote metastasis. We found that SMOC2 induced mesenchymal-like morphology and activities in both RCC and non-RCC kidney epithelial cell lines. Mechanistically, treatment of RCC cell lines ACHN and 786-O with SMOC2 (recombinant and enforced expression) caused a significant increase in EMT-markers, -matrix production, -proliferation, and -migration, which were inhibited by targeting SMOC2 by siRNA. We further characterized SMOC2 activation of EMT to occur through the integrin ß3, FAK and paxillin pathway. The proliferation and metastatic potential of SMOC2 overexpressing ACHN and 786-O cell lines were validated in vivo by their significantly higher tumor growth in kidneys and systemic dissemination into other organs when compared to their respective controls. In principle, understanding the impact that SMOC2 has on EMT may lead to more evidence-based treatments and biomarkers for RCC metastasis.

Comparison of Complement Pathway Activation in Autoimmune Glomerulonephritis.

Introduction: Studies on complement activation have implicated a combination of the classical pathway (CP), lectin pathway (LP), and alternative pathway (AP) in triggering the terminal pathway (TP) for each common autoimmune glomerulonephritis (GN). Evaluating different pathways simultaneously may help identify whether one is preferentially activated and, consequently, which is best to target for each disease. Methods: We followed 112 patients with focal segmental glomerular sclerosis (FSGS), membranous nephropathy (MN), IgA nephropathy (IgAN), lupus nephritis (LN), and antineutrophil cytoplasmic autoantibody-associated vasculitis (AAV) for a median duration of 22 (12-52) months. At the time of greatest clinical activity, we simultaneously evaluated urinary C3a (C3 convertase activity), C5a and sC5b-9 (TP), MASP-1 and MASP-2 (LP), C1q (CP), C4a (CP/LP), and Ba and Bb (AP). We evaluated the relation between activation fragments of the AP and CP/LP with the TP. Results: Urinary complement biomarkers for each pathway were associated with the severity of proteinuria. Fragments of the TP were higher among patients with FSGS and MN compared with patients with IgAN, LN, and AAV. For the AP, urinary Ba level was lower in those with IgAN and LN compared with those with FSGS. For the CP/LP, urinary C4a, MASP-1, and MASP-2 levels were similar between diseases whereas urinary C1q levels were lower in those with LN. For each GN, independent associations existed between the activation markers of the AP and CP/LP with the degree of TP activation, except for the AP in AAV, although perhaps underpowered. Conclusion: The AP and CP/LP contribute individually to the TP activation in autoimmune GN, and both seem to be valid potential therapeutic targets.

Subchronic oral exposure of tungsten induces myofibroblast transformation and various markers of kidney fibrosis.

Tungsten is a naturally occurring transition element used in a broad range of applications. As a result of its extensive use, we are increasingly exposed to tungsten from our environment, including potable water, since tungsten can become bioaccessible in ground sources. The kidneys are particularly susceptible to tungsten exposure as this is the main site for tungsten excretion. In this study, we investigated the prolonged effects of tungsten on the kidneys and how this may impact injury and function. When mice were exposed to tungsten in their drinking water for 1 mo, kidney function had not significantly changed. Following 3-mo exposure, mice were presented with deterioration in kidney function as determined by serum and urine creatinine levels. During 3 mo of tungsten exposure, murine kidneys demonstrated significant increases in the myofibroblast marker α-smooth muscle actin (αSMA) and extracellular matrix products: fibronectin, collagen, and matricellular proteins. In addition, Masson's trichrome and hematoxylin-eosin (H&E) staining revealed an increase in fibrotic tissue and vacuolization of tubular epithelial cells, respectively, from kidneys of tungsten-treated mice, indicative of renal injury. In vitro treatment of kidney fibroblasts with tungsten led to increased proliferation and upregulation of transforming growth factor ß1 (TGFß1), which was consistent with the appearance of fibroblast-to-myofibroblast transition (FMT) markers. Our data suggest that continuous exposure to tungsten impairs kidney function that may lead to the development of chronic kidney disease (CKD).

Qualitative and Quantitative Dosage of the Anti M-Type Phospholipase A2 Receptor Autoantibody: One-Year Experience in Quebec's Reference Center.

BACKGROUND: Quantification of the M-type phospholipase A2 receptor antibodies (anti-PLA2R) is now an essential tool for diagnosis and management of primary membranous nephropathy (MN). Since October 2018, Hôpital Maisonneuve-Rosemont (HMR) has been designated as Quebec's reference center for serum anti-PLA2R antibody testing by the Institut National d'Excellence en Santé et Services Sociaux (INESSS), the regulatory body on drugs and tests usage in Quebec. OBJECTIVES: To describe the 2-step method of serum qualitative and quantitative anti-PLA2R antibody testing during its first year of use in Quebec and analyze its diagnostic value in the province's population. DESIGN: Retrospective cohort study. SETTING: Single-center academic teaching hospital in Quebec, Canada. PATIENTS: All patients who had a serum anti-PLA2R antibody test analyzed at HMR from October 1, 2018, to October 1, 2019, were included in the study. MEASUREMENTS: Serum anti-PLA2R antibodies were screened by indirect immunofluorescence tests. If results were positive or undetermined, it was followed by a quantitative enzyme-linked immunosorbent assay (ELISA) test. Both tests were based on a commercial kit developed by the same company. METHODS: We calculated sensitivity, specificity, predictive value, and likelihood ratio for both tests, using kidney biopsy findings performed at HMR as the gold standard. RESULTS: In Quebec, a total of 1690 tests were performed among 1025 patients during the study year. A small proportion of these patients (8%) were followed at HMR. Patients tested at HMR and in the rest of Quebec had similar characteristics. Test validity was only characterized for patients tested at HMR. Sensitivity and specificity were, respectively, 58% and 100% for the qualitative test, and 71% and 100% for the quantitative test. The combined net sensitivity was 42% and the net specificity 100%. The net positive and negative predictive value were 100% and 84% respectively, whereas the net negative likelihood ratio was 0.58. LIMITATIONS: As the detailed analysis was only possible in the small proportion of patients clinically followed at HMR, there is a possible selection bias. Another potential selection bias was the focus on patients who were selected to have a kidney biopsy, probably because of more severe disease, higher probability of glomerulonephritis, or lesser number of comorbidities. Given the retrospective nature of this study, there was no systematic kidney biopsy or serum PLA2R antibody testing performed. Finally, we were unable to provide detailed information on the timing between immunosuppressive therapy and anti-PLA2R results. CONCLUSIONS: Serum anti-PLA2R antibody testing was widely used in Quebec during its first year of availability. A 2-step approach, using a qualitative test first, followed by a quantitative test if the results are positive or undetermined, appears efficient to avoid useless quantitative testing in negative patients and to better characterize undetermined results on immunofluorescence. TRIAL REGISTRATION: Due to the retrospective nature of this study, no trial registration was performed.

CONTEXTE: La quantification des anticorps des récepteurs de la phospholipase A2 de type M (anti-PLA2R) est désormais un outil essentiel pour le diagnostic et la prise en charge de la glomérulonéphrite extra-membraneuse primaire (GEMp). Depuis octobre 2018, l'Hôpital Maisonneuve-Rosemont (HMR) a été désigné par l'Institut National d'Excellence en Santé et Services Sociaux (INESSS)­l'organisme règlementant l'usage des médicaments et des tests au Québec­comme le centre hospitalier de référence dans la province pour le dépistage des anticorps sériques anti-PLA2R. OBJECTIFS: Décrire la méthode en deux étapes du test qualitatif et quantitatif des anticorps anti-PLA2R sériques au cours de sa première année d'utilisation au Québec et évaluer sa valeur diagnostique dans la population de la province. TYPE D'ÉTUDE: Étude de cohorte rétrospective. CADRE: Un centre hospitalier universitaire du Québec (Canada). SUJETS: Ont été inclus tous les patients dont le test des anticorps sériques anti-PLA2R a été analysé à HMR entre le 1er octobre 2018 et le 1er octobre 2019. MESURES: Les anticorps sériques anti-PLA2R ont été détectés par immunofluorescence indirecte. Les résultats positifs ou indéterminés ont été suivis d'un test ELISA quantitatif. Les deux tests ont été réalisés à l'aide de trousses commerciales développées par la même entreprise. MÉTHODOLOGIE: Nous avons analysé la sensibilité, la spécificité, la valeur prédictive et le rapport de vraisemblance des deux tests avec comme référence des résultats de biopsie rénale obtenus à HMR. RÉSULTATS: Au Québec, au cours de l'année de l'étude, 1 690 tests ont été effectués sur 1 025 patients; une faible proportion de ces patients (8 %) étaient suivis à HMR. Les patients, qu'ils aient été testés à HMR et ailleurs au Québec, présentaient des caractéristiques semblables. La validité du test n'a été caractérisée que pour les patients testés à HMR. La sensibilité et la spécificité s'établissaient respectivement à 58 % et à 100 % pour le test qualitatif, et à 71 % et 100 % pour le test quantitatif. La sensibilité nette combinée était de 42 % et la spécificité nette, de 100 %. Les valeurs prédictives nettes, positive et négative, étaient respectivement de 100 % et de 84 %, alors que le ratio net de probabilité négative était de 0,58. LIMITES: L'étude présente un possible biais de sélection puisque l'analyse détaillée n'était possible que pour la faible proportion de patients suivis à HMR. L'accent mis sur les patients sélectionnés pour une biopsie rénale, probablement en raison d'une maladie plus grave, d'une probabilité plus élevée de glomérulonéphrite ou d'un moins grand nombre de comorbidités, constitue un autre possible biais de sélection. Aucune biopsie rénale ou test d'anticorps de PLA2R sérique systématique n'a été effectué puisque l'étude est rétrospective. Enfin, il n'a pas été possible de fournir des informations détaillées sur le temps écoulé entre le traitement immunosuppresseur et les résultats du test d'anticorps anti-PLA2R. CONCLUSION: Le test d'anticorps sériques anti-PLA2R a été largement utilisé au Québec au cours de sa première année de disponibilité. Une approche en deux étapes, constituée d'un test qualitatif suivi d'un test quantitatif si le résultat est positif ou indéterminé, semble efficace pour éviter de procéder inutilement à des tests quantitatifs chez les patients négatifs et pour caractériser plus précisément les résultats indéterminés par immunofluorescence. ENREGISTREMENT DE L'ESSAI: L'essai n'a pas été enregistré puisqu'il s'agit d'une étude rétrospective.