In patients with significant GI bleeding, the most important laboratory test is to type and crossmatch blood. Another important laboratory test is the complete blood count. Additionally, blood urea nitrogen (BUN), creatinine, electrolyte, glucose, and coagulation studies, as well as liver function studies, should be considered. The initial hematocrit level often will not reflect the actual amount of blood loss. Upper tract hemorrhage may elevate the BUN through digestion and absorption of hemoglobin. Coagulation studies, including prothrombin time, partial thromboplastin time, and platelet count, are of obvious benefit in patients taking anticoagulants or those with underlying hepatic disease. An electrocardiogram should be considered in patients in the coronary artery disease age group. Silent ischemia can occur secondary to the decreased oxygen delivery accompanying significant GI bleeding and, thus, supplemental oxygen is advised for such patients.
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