Lower gastrointestinal bleeding laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Laboratory Findings

The minimum essential blood work in diagnosing lower gastrointestinal bleeding includes a complete blood count, renal function and liver function tests, and coagulation studies. Although not diagnostic, a blood type and crossmatch should be done in patients who present with life-threatening bleeding.

Complete blood count

• Complete blood count may show a low hemoglobin level or a drop from a previous baseline level.
• In acute blood loss, the initial hemoglobin level may be normal but will fall with fluid resuscitation.
• Other abnormalities, such as thrombocytopenia, may point to a variceal source of bleeding.
• The presence of uremia or a history of aspirin or clopidogrel use should be noted, as both factors can significantly affect platelet function without causing thrombocytopenia. *A raised leukocyte count may point to an infectious or inflammatory cause.

Renal function tests

• Abnormal values of renal function tests of may indicate underlying kidney disease, a condition associated with increased risk for gastrointestinal bleeding.
• A disproportionately raised urea nitrogen level may suggest bleeding from an upper gastrointestinal source or hemoconcentration.
• Intravenous contrast for angiograms must be administered with caution in patients with renal impairment to avoid the risk of contrast nephropathy.

Liver function tests

• Persons with an underlying liver disease are at increased risk of gastrointestinal bleeding, and bleeding may be more difficult to control due to coagulopathy associated with liver dysfunction.
• Abnormal liver function may suggest the presence of colorectal varices.

Coagulation studies

• An elevated INR may indicate anticoagulation with warfarin or may be evidence of severe liver dysfunction.
• A prolonged aPTT is seen in anticoagulation with heparin.

Blood type and cross match

• Identifies blood groups A, B, AB, O and Rhesus (Rh) factor.
• Essential in the management of hemodynamically unstable patients who may need a blood transfusion.