Immunoglobulin abnormalities are frequent in infective endocarditis. Circulating immune complexes have been demonstrated in more than 90 percent of patients with infective endocarditis. Hyperglobulinemia is common when the illness is prolonged. Occasionally, there have been reports of patients with IgG or IgM M components in their serum. Serum complement levels are low in some patients, particularly when endocarditis is complicated by immune complex glomerulonephritis.
Renal abnormalities are common, and most patients have proteinuria and microscopic hematuria.
Elevated levels of creatinine accompany the development of extensive immune deposit glomerulonephritis. The occasional occurrence of drug-induced interstitial nephritis during treatment with a penicillin must be distinguished from diffuse glomerulonephritis. Whereas glomerulonephritis is usually present when endocarditis is diagnosed, interstitial nephritis begins after several weeks of therapy and may be accompanied by other signs of drug allergy or eosinophils in the urine sediment. In most patients with SBE, all blood cultures taken before initiation of antibiotic therapy are positive, reflecting the sustained bacteremia associated with an infected endothelial surface. Three to four sets of cultures taken before the start of therapy are adequate for demonstrating the bacteremia.