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Abstract Background Culture-negative infective endocarditis (IE) constitutes approximately 10% of all cases of IE. Bartonella endocarditis is a common cause of culture-negative endocarditis and is associated with a high mortality rate. To date, no cases of Bartonella IE has been reported in association with cryoglobulinemia in the UK. We present a unique case of Bartonella IE causing secondary cryoglobulinemia in a young female. Case presentation A 17-year-old female with a background of pulmonary atresia and ventricular septal defect repaired with a cardiac conduit at the age of 4, presented with a one-year history of weight loss (from 53 to 39 kg) and poor appetite. She subsequently developed a vasculitic rash and haematoproteinuria with decline in renal function, requiring urgent hospital admission. Initial blood tests showed a near normal creatinine, but a raised cystatin C. Renal biopsy showed focal necrotizing glomerulonephritis with no acute tubular necrosis or chronic change. Subsequent blood tests supported a diagnosis of cryoglobulinaemic vasculitis (high rheumatoid factor, low complement, polyclonal gammopathy, Type 3 cryoglobulin). A weak positive PR3 meant there was some uncertainty about whether this could be a primary ANCA-associated vasculitis (AAV). Initial workup for an infectious cause, including multiple blood cultures, were negative. However, an echocardiogram showed definite vegetations on her surgical conduit. The patient did not respond to empirical antimicrobials and so was referred for surgical revision of her conduit. Tissue samples obtained intra-operatively demonstrated Bartonella species. With targeted antimicrobials post-operatively, she improved with resolution of immunologic abnormalities and at last review had a normal renal profile. On reviewing her social history, she had adopted several stray cats in the preceding year; and thus, the cause of the Bartonella infection was identified. Conclusion This is the first reported case of Bartonella endocarditis causing secondary cryoglobulinemia reported in the UK. The key learning points from this case include that Bartonella endocarditis can present as a cryoglobulinaemic vasculitis and should be considered in any differential when the cause of cryoglobulinaemia is not clear and to enquire about relevant exposures especially when culture-negative endocarditis is suspected.