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]

Overview

The essential laboratory workup in the management of lower gastrointestinal bleeding includes a complete blood count, renal function test, liver function tests, and coagulation studies. In patients with life-threatening bleeding, although not diagnostic, a blood type and crossmatch should be done.

Laboratory Findings

Laboratory findings in patients presenting with lower gastrointestinal bleeding include:

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 can significantly affect platelet function without causing thrombocytopenia.
• Leukocytosis may point to an infectious or inflammatory cause.

Renal function tests

• Abnormal values of renal function tests may indicate underlying kidney disease. Chronic kidney disease CKD is associated with increased risk for gastrointestinal bleeding by disrupting platelet function.
• The presence of uremia may suggest bleeding is from an upper gastrointestinal source.
• Intravenous contrast for angiograms must be administered with caution in patients with renal impairment to avoid the risk of contrast nephropathy.

Liver function tests

• Patients with an underlying liver disease are at increased risk of gastrointestinal bleeding.
• Bleeding will be more difficult to control due to coagulopathy associated with liver dysfunction. Hence LFT's are recommended to assess the severity of liver damage.
• Abnormal liver function without any previous history of liver disease 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

• Blood type and cross match identifies blood groups A, B, AB, O and Rhesus (Rh) factor.
• Blood type and cross match is essential in the management of hemodynamically unstable patients who may need a blood transfusion.

Fecal Occult Blood Testing

• Fecal occult blood test (FOBT's) have sufficient sensitivity to detect bleeding that is not visible in the stool.
• Three types of FOBT are currently employed.
  • Guaiac-based tests
  • Heme-porphyrin tests
  • Immuno-chemical tests

Types of FOBT	MOA	Causes of False-Positive
Guaiac-based tests Hemoccult II Hemoccult II SENSA	Pseudo-peroxidase activity of hemoglobin turns the guaiac compound blue in the presence of hydrogen peroxide.	Red meat consumption (nonhuman hemoglobin) Fruit consumption (cantaloupe, grapefruit, figs)
Heme-porphyrin tests HemeSelect FECA-EIA	HemoQuant, measures hemoglobin-derived porphyrins Allowing quantitative measurement of hemoglobin in stool	Extraintestinal blood loss Epistaxis Gingival bleeding Tonsillitis/pharyngitis Hemoptysis
Immuno-chemical tests	Detects intact human hemoglobin. Immunochemical FOBTs do not detect digested hemoglobin They are not able to detect bleeding from upper gastrointestinal sources	No false positives

Blood in stools

Abdominal pain

Yes

No

Fever

Rectal pain

Yes

No

H/O of constipation

H/O of constipation

No

Yes

No

Yes

Weightloss

Diverticulosis

Hemodynamic status

Diverticulitis

No

Yes

Stable

Unstable

Polyps

Colon cancer

Ischemic colitis

Stool culture

Positive

Negative

No

Yes

Infectious colitis

Inflammatory bowel disease

Weight Loss

Anal fissure External Hemmrhoids

Yes

No

Rectal cancer Colon cancer

Angiodysplasia Polyps