Kidney Week

Abstract: FR-PO0762

The ANCA-Cryoglobulin Trap: Bartonella Endocarditis Presenting as Crescentic Glomerulonephritis

Session Information

• Glomerular Diseases: ANCA Vasculitis, Anti-GBM Disease, and Crescentic GN
  October 23, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics

Authors

• Zatreh, Mallak, The University of Kansas Medical Center, Kansas City, Kansas, United States

Mallak Zatreh, MD

• Kirby, Grant Thomas, The University of Kansas Medical Center, Kansas City, Kansas, United States

Grant Thomas Kirby, MD

Introduction

Infection-related glomerulonephritis can present with several features that resemble autoimmune vasculitis. Bartonella is a known cause of culture-negative endocarditis that can present with an immune complex mediated crescentic glomerulonephritis with misleading serologies.

Case Description

A 64-year-old male with hypertension, CKD stage III, prior bioprosthetic aortic valve replacement for endocarditis, and history of IV drug use presented with acute right upper extremity ischemia requiring emergent thrombectomy. He reported recent cat exposure. Exam showed a purpuric rash over the lower extremities.

Labs showed creatinine of 6.2 mg/dL (baseline 1.5) and thrombocytopenia (50 x 10⁹/L). Urinalysis with hematuria, proteinuria (UPCR 1.8 g/g), and RBC casts. Further workup demonstrated low complements (C3 62 mg/dL, C4 9 mg/dL), negative ANA, and positive rheumatoid factor, PR3-ANCA (160), and type III cryoglobulins. Peripheral smear showed no schistocytes.

Blood cultures and transthoracic echocardiogram were normal. Transesophageal echocardiogram ultimately showed a small vegetation on his bioprosthetic valve. Kidney biopsy demonestrated focal proliferative crescentic glomerulonephritis with IgM-dominant deposition and C3/C1q staining. Evaluation for culture-negative endocarditis confirmed Bartonella infection by serology and plasma microbial cell-free DNA.

He was treated with doxycycline and rifampin; immunosuppression was deferred. AKI progressed, necessitating dialysis, but subsequently achieved renal recovery with eGFR stabilization in the 20s. In the absence of clear guidance for Bartonella-associated prosthetic valve endocarditis, he was continued on long-term suppressive doxycycline.

Discussion

Bartonella endocarditis is an important cause of culture-negative endocarditis that can mimic vasculitis. PR3-ANCA positivity, low complements, and cryoglobulinemia may lead to misdiagnosis. Patients with prosthetic valves and relevant exposures require a high index of suspicion. Early recognition is essential, as treatment of the underlying infection is paramount and immunosuppression may be harmful.

(A) LM: crescentic GN. (B-C) IF: IgM/IgG mesangial deposition, consistent with immune complex GN