Diagnostic StudiesLaboratory Tests. Most patients over age 50 with leg edema have venous insufficiency, but if the etiology is unclear, a short list of laboratory tests will help rule out systemic disease: complete blood count, urinalysis, electrolytes, creatinine, blood sugar, thyroid-stimulating hormone, and albumin. A serum albumin below 2 g/dL often leads to edema and can be caused by liver disease, nephrotic syndrome, or protein-losing enteropathy.[14] Additional tests are indicated depending on the clinical presentation:Patients who may have a cardiac etiology should have an electrocardiogram, echocardiogram, and chest radiograph. Dyspneic patients should have a brain natriuretic peptide (BNP) determination to help detect heart failure. The BNP is most helpful for ruling out (rather than ruling in) heart failure because the sensitivity is high (90%).[23]Idiopathic edema can be diagnosed in young women without further testing if there is no reason to suspect another etiology based on history and physical examination.[5] However, tests to confirm idiopathic edema have been described and may be helpful in difficult cases ( Table 5 ).[12,24]In patients with acute edema (<72 hours), a normal D-dimer will essentially rule out deep vein thrombosis if the clinical suspicion is low because false negative D-dimers are rare.[25-27] However, an elevated D-dimer should be followed up with a Doppler examination because false positive D-dimers are common.[28] The variability among laboratory assays has been problematic, but a recent systematic review recommended the rapid quantitative ELISA as the most useful test.[25]Patients with possible nephrotic syndrome should have serum lipids in addition to the basic laboratory studies listed above.Imaging Studies. Patients over age 45 with edema of unclear etiology should have an echocardiogram to rule out pulmonary hypertension.[4] Lymphoscintigraphy can be helpful to distinguish lymphedema from venous edema and to determine the cause of lymphedema. Lymphoscintigraphy is performed by injecting a radioactive tracer into the first web space and monitoring lymphatic flow with a gamma camera.[13]
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