Laboratory Studies C

Blood cultures are the essential laboratory test for the diagnosis and treatment of IE. Typically, patients with IE have a low-grade consistent bacteremia, with approximately 80% of cases having less than 100 CFU/mL in the bloodstream.1 Blood culture results are criticalfor determining the most appropriate therapy. Three blood culture sets should be drawn within the initial 24 hours to determine the etiologic agent. Approximately 90% of the first two cultures will yield a positive result. If a positive blood culture is not obtained from a patient with suspected IE, the microbiology laboratory should be notified and cultures requested to be monitored for growth of fastidious organisms for up to 1 month.

FIGURE 74-3. A. Conjunctival petechiae. (From Wolff K, Johnson RA, Suurmond D. In: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. New York: McGraw Hill. Copyright 2005.) B. Splinter hemorrhage. (From Collins SP. In: Atlas of Emergency Medicine, 2nd ed. New York: McGraw Hill. Copyright 2002.) C. Clubbing of finger. (From Tosti A, Piraccini BM. In: Fitzpatrick's Dermatology in General Medicine, 7th ed. New York: McGraw Hill. Copyright 2007.) D. Osler's nodes. (From Collins SP. In: Atlas of Emergency Medicine, 2nd ed. New York: McGraw Hill. Copyright 2002.) E. Janeway's lesions. (From Wolff K, Johnson RA, Suurmond D. In: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. New York: McGraw Hill. Copyright 2005.) F. Roth's spots (From Effron D, Forcier BC, Wyszynski RE. In: Atlas of Emergency Medicine, 2nd ed. New York: McGraw Hill. Copyright 2002.)

^^ Another important tool aiding in the diagnosis of IE is the echocardiogram. This imaging tool is used to visualize vegetations. Two methods of the echocardiogram are used: the transthoracic echocardiogram (TTE) and the transesophageal echocardiogram (TEE). The TTE has been used since the 1970s; however, it is less sensitive (58-63%) than the TEE (90-100%).10 Despite the TEE being more sensitive, use of the TTE for patients with suspected native-valve IE is usually sufficient.11,12 The TEE may be used as a secondary test for patients whose TTE was negative and in whom a high clinical suspicion of IE exists. Additionally, a TEE is often preferred in patients who have complicated disease, including left-sided IE, prosthetic valves, or perivalv-ular extension of the vegetation. ' Echocardiograms also may be employed to assess

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the need for surgical intervention or to determine the possible source of emboli. '

Additional nonspecific tests for IE may be performed. These include hematologic parameters to determine whether the patient is anemic, which occurs in a majority of patients. The WBCs may be elevated, particularly in acute disease. However, in a subacute infection, the WBCs may be normal. An erythrocyte sedimentation rate (ESR) may also be obtained to determine the presence of inflammation, although this test is highly nonspecific and almost always elevated in IE.

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