Background/Purpose: Antiphospholipid antibody (aPL)-associated nephropathy (aPL-N) is recognized as a distinct complication of APS. However, it remains unclear whether pathologists worldwide use uniform diagnostic criteria to distinguish aPL-N from other forms of thrombotic microangiopathy. In parallel with international efforts to develop new classification criteria for antiphospholipid syndrome (APS), we conducted a pilot study to assess the renal pathologic features used by academic pathologists to diagnose aPL-N.

Methods: We conducted a web-based survey of 780 members of an international Renal Pathology Society in 50 countries. We asked respondents to determine whether two acute and eight chronic aPL-N features were consistent with acute or chronic aPL-N without providing aPL serology. and rate each item using a Likert scale (from +5 to -5): “Please consider two renal biopsies which are exactly the same except that one has the pathologic feature presented below and the other does not. Please rate how specific each feature is in differentiating “acute” or “chronic” aPL nephropathy from other diagnoses. They were also asked to rate their confidence in diagnosing aPL nephropathy on renal biopsy in two scenarios: 1) without aPL laboratory test results, or 2) with known lupus.

Results: Survey response rate was 14% (111/780) and 91% of participants self-identified as renal pathologists from 33 countries and in clinical practice for a mean (SD) of 19.1 (15.1) years. Over 92% of respondents agreed that thrombotic microangiopathy lesions in the glomeruli, arterioles, or arteries were consistent acute aPL-N, and >75% gave a positive Likert scale score ( >0), with >50% indicating Likert score +3 to +5. For chronic aPL-N, >83% agreed with the pathologic features of organized arterial or arteriolar microthrombi with or without recanalization, organized glomerular thrombi, and fibrous and fibrocellular (arterial or arteriolar) occlusions, and >50% indicated a positive Likert score ( >0), while there was less consensus for other chronic features (Table). The majority of respondents (76%) reported either an equivocal (Likert score of 0, 18%) or lack of confidence (score from -1 to -5, 58%) in diagnosing aPL-N on renal biopsy without of aPL laboratory test results. However, 80% indicated confidence (Likert score >0) in diagnosing aPL-N with concomitant lupus (69%) indicated Likert score +3 to +5.

Conclusion: Consensus exists among over 90% of pathologists worldwide that the following renal pathologic features are most specific for aPL-N: 1) non-inflammatory glomerular or small arterial microthrombi and 2) organized microvascular thrombi with recanalization. However, in the absence of serologic aPL status, over 75% of pathologists indicated lack of specificity of chronic glomerular or small arterial changes for aPL-N. Over 80% of pathologists indicated high confidence in diagnosing aPL nephropathy in patient with concomitant lupus. These findings indicate the importance of aPL serologic test results in biopsy interpretation and suggest higher specificity for certain acute or chronic features.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterization-of-antiphospholipid-antibody-associated-nephropathy-an-international-survey-of-renal-pathology-society-members/