1. Clinical Presentation and Initial Assessment

Acute Lower Gastrointestinal Bleeding (LGIB) typically presents as hematochezia with varying stool color and may be accompanied by hemodynamic instability. Early recognition informs subsequent diagnostic and therapeutic steps.

Hematochezia Patterns:

• Bright red blood per rectum: Often suggests a distal colon or rectal source.
• Maroon/dark stools: May indicate a proximal colonic or small-bowel origin, or rapid transit of blood.
• Profuse, sudden bleeding: Can be indicative of arterial sources such as diverticular bleeding or angiodysplasia.
• Intermittent/scant bleeding: More commonly associated with inflammatory, ischemic, or neoplastic etiologies.

Hemodynamic Signs:

• Tachycardia (>100 beats per minute), hypotension (systolic blood pressure <90 mmHg), and orthostasis (a decrease in SBP ≥20 mmHg or an increase in heart rate ≥20 bpm upon standing) are key indicators of significant blood loss.
• Syncope, dizziness, or altered mental status can signal severe hypoperfusion.

Associated Findings:

• The presence or absence of abdominal pain can be diagnostic: pain may suggest ischemic colitis or an IBD flare, whereas painless bleeding is characteristic of diverticular disease or angiodysplasia.
• A thorough medication history is crucial, noting use of anticoagulants, antiplatelets, NSAIDs, or immunosuppressants.

2. Laboratory Evaluation

Laboratory tests are essential to quantify blood loss, identify coagulopathies, and prepare for potential transfusions.

A. Complete Blood Count (CBC)

• Obtain a baseline hemoglobin and hematocrit. It’s important to recognize that in acute, rapid blood loss, these values may not immediately reflect the true extent of hemorrhage due to lack of time for hemodilution.
• Serial drops in hemoglobin (>2 g/dL within 24 hours) are indicative of active or severe bleeding.
• A reticulocyte count can help differentiate acute blood loss (where reticulocytes would be elevated after a delay) from chronic anemia (where reticulocytes might be inappropriately low or normal).

B. Coagulation Studies

• Prothrombin Time/International Normalized Ratio (PT/INR) and activated Partial Thromboplastin Time (aPTT) are crucial for detecting the effects of warfarin, underlying liver dysfunction, or defects in the intrinsic coagulation pathway.
• Standard coagulation assays often do not accurately reflect the anticoagulant effect of Direct Oral Anticoagulants (DOACs). Clinical assessment should rely on the timing of the last dose. Consider specialized testing (e.g., anti-Xa activity for Factor Xa inhibitors, dilute thrombin time for dabigatran) if available and clinically indicated.
• Early identification of coagulopathy is critical for guiding reversal strategies (e.g., 4-Factor Prothrombin Complex Concentrate [4F-PCC] for Vitamin K Antagonists; idarucizumab for dabigatran; andexanet alfa for factor Xa inhibitors).

C. Type & Crossmatch

• Ensure immediate availability of compatible packed red blood cells (PRBCs) by performing a type and crossmatch.
• Activate the Massive Transfusion Protocol (MTP) if anticipating the need for ≥4 units of PRBCs within 1–2 hours or ≥10 units within 24 hours.

3. Imaging and Other Modalities

Imaging modalities are employed to localize the source of bleeding, particularly when endoscopic evaluation is delayed, non-diagnostic, or unfeasible.

CT Angiography (CTA)

• CTA can detect active arterial bleeding at rates of ≥0.3 mL/min with a reported sensitivity of approximately 85% and specificity of around 92%.
• It offers rapid localization of the bleeding site, which is invaluable for guiding subsequent interventional radiology procedures or surgical planning.

Radionuclide RBC Scan (Tagged Red Blood Cell Scan)

• This modality can detect slower rates of bleeding (≥0.1 mL/min) compared to CTA.
• However, it has a longer acquisition time and provides poorer spatial resolution, making precise localization challenging.

Capsule Endoscopy / Deep Enteroscopy

• These techniques are generally reserved for cases of obscure or recurrent gastrointestinal bleeding after both colonoscopy and CTA have failed to identify a source. They are primarily used for evaluating the small bowel.

4. Risk Stratification and Scoring Systems

Risk stratification scores can aid in triage decisions and prognostication but must always be integrated with thorough clinical judgment.

A. Adapted Glasgow-Blatchford Score (GBS)

• Variables included in the GBS are blood urea nitrogen, hemoglobin level, systolic blood pressure, heart rate, and presence of comorbidities such as liver disease or heart failure.
• While originally developed and validated for upper GI bleeding, its performance in LGIB is limited. It may particularly underestimate the severity in patients with brisk, hemodynamically significant bleeds.

B. Oakland Score

• Variables specifically for LGIB include: age, sex, history of prior LGIB, digital rectal exam findings (blood), heart rate, systolic blood pressure, and hemoglobin level.
• A score of ≤8 points has been shown to predict a ≥95% probability of safe discharge from the emergency department without the need for hospital-based intervention (transfusion, endoscopic therapy, surgery, or in-hospital death).

C. Clinical Integration

• Low-risk patients (e.g., Oakland score ≤8, stable vital signs, no major comorbidities, bleeding ceased) may be considered for outpatient management with prompt follow-up.
• High-risk patients (e.g., ongoing bleeding, hemodynamic instability, significant comorbidities, high Oakland score) require hospital admission, close monitoring, and expedited diagnostic evaluation (colonoscopy or CTA).

5. Initial Management and Transfusion Strategies

The primary goals of initial management are to restore hemodynamic stability and tissue perfusion while employing evidence-based transfusion strategies that balance benefits with potential risks.

A. Hemodynamic Resuscitation

• Initiate resuscitation with isotonic crystalloids (e.g., normal saline or balanced salt solutions like Lactated Ringer’s).
• If hypotension persists despite adequate intravenous fluid resuscitation, vasopressor support should be initiated. Norepinephrine is typically the first-line agent.

B. Blood Product Transfusion

Current guidelines advocate for a restrictive transfusion strategy in most stable patients with LGIB.

• Restrictive strategy for most stable patients:
  • Transfuse packed red blood cells (PRBCs) when hemoglobin level drops below 7 g/dL.
  • The target hemoglobin range post-transfusion is typically 7–9 g/dL.
• Liberal strategy for selected patients:
  • Consider a higher transfusion threshold (hemoglobin <8 g/dL) and target (≥10 g/dL) for patients with active cardiac ischemia (e.g., acute coronary syndrome) or significant underlying cardiovascular disease where higher oxygen-carrying capacity may be beneficial.

Component Selection:

• Packed Red Blood Cells (PRBCs): Primarily for correcting anemia and improving oxygen-carrying capacity.
• Platelets: Transfuse if platelet count is <50,000/µL in the setting of active bleeding.
• Plasma (Fresh Frozen Plasma or other plasma products): Indicated for correction of coagulopathy (e.g., INR >1.5-2.0) when specific reversal agents are unavailable or insufficient, or in the context of massive transfusion.

Monitoring:

• Closely monitor vital signs (heart rate, blood pressure), urine output, and mental status.
• Perform serial hemoglobin measurements to assess response to transfusion and detect ongoing bleeding.
• Be vigilant for signs of transfusion reactions, including Transfusion-Associated Circulatory Overload (TACO) and Transfusion-Related Acute Lung Injury (TRALI).