Improvement of indirect immunofluorescence technique to detect antineutrophil cytoplasmic antibodies and its impact on test positivity rate

The indirect immunofluorescence (IIF) technique for antineutrophil cytoplasmic antibodies (ANCA) detection is subject to substantial differences across laboratories. This study aimed to assess the impact of improvements in the IIF-ANCA technique on the positivity rate of ANCA tests. A cross-sectional study was performed with serum samples from patients with ANCA-associated vasculitis (AAV), autoimmune hepatitis (AIH), and ulcerative colitis (UC). A paired analysis was performed for IIF-ANCA results using the traditional method and a modified protocol after a series of specific adjustments in the technique based on the protocol of IIF-ANCA test performed at a nation-wide private laboratory in Brazil. ANCA specificity was assessed by ELISA for anti-proteinase 3 (PR3) and anti-myeloperoxidase (MPO) antibodies. Sixty-one patients were evaluated. The positivity rate of IIF-ANCA tests at disease presentation performed at the University reference laboratory was 32.3% in AAV, AIH, and UC patients, whereas the positivity rates of IIF-ANCA and ELISA tests in other laboratories were 75.0 and 72.7%, respectively. After modifications in the IIF-ANCA technique, there was a significant increase in the positivity rate (14.8 vs 34.3%; P=0.0002) and in median titers [1/40 (1/30-1/160) vs 1/80 (1/40-1/80); P=0.0003] in AAV, AIH, and UC patients. UC had the highest increment in positive results from 5.3 to 36.8%. There was poor agreement between MPO- or PR3-ANCA and both IIF-ANCA techniques. In conclusion, modifications in the IIF-ANCA protocol led to a significant improvement in its positivity rate and titers.

Endocarditis por bartonella asociada a glomerulonefritis y neurorretinitis / Bartonella endocarditis associated with glomerulonephritis and neuroretinitis

La endocarditis bacteriana con hemocultivo negativo constituye un dilema diagnóstico. Tanto Bartonella como Coxiella pueden causarla, con presentaciones clínicas similares que pueden simular una vasculitis sistémica no infecciosa. Sin embargo, difieren en el tipo y la duración del tratamiento, por lo que es fundamental identificar el agente etiológico. Presentamos un caso de endocarditis por Bartonella henselae asociada a glomerulonefritis y neurorretinitis, con hemocultivo negativo, anticuerpos anticitoplasma de neutrófilos y antiproteinasa 3 positivos, y serología positiva para Bartonella con reacción cruzada para Coxiella burnetti. El diagnóstico etiológico fue confirmado a posteriori mediante amplificación y secuenciación parcial del gen ribC a partir de tejido de la válvula cardíaca. El paciente recibió tratamiento antibiótico e inmunosupresor seguido de recambio valvular aórtico y presentó evolución favorable.

Blood-culture negative endocarditis is a diagnostic challenge. Both Bartonella and Coxiella can cause it with similar clinical presentations mimicking a systemic vasculitis. The identification of the etiologic agent is essential because they differ in treatment type and duration. We present a case of blood-culture negative endocarditis caused by Bartonella henselae, associated with glomerulonephritis and neuroretinitis, with negative blood culture, positive anti-neutrophil cytoplasmic and antiproteinase 3 antibodies. The serology was positive for Bartonella with cross-reactivity to Coxiella burnetti. The etiological diagnosis was achieved by polymerase chain reaction amplification and sequencing of a ribC gene fragment. The patient received antibiotic and immunosuppressive treatment followed by replacement of the aortic valve with favorable medium-term evolution.