In a 70‑year‑old man with a history of deep‑vein thrombosis who is taking a direct oral anticoagulant and now presents with one day of bright red blood per rectum, what laboratory studies and imaging investigations should be ordered?

Immediate Colonoscopy with Anoscopy After Hemodynamic Stabilization and Coagulation Assessment

This patient requires urgent colonoscopy within 24 hours to directly visualize the bleeding source, given the CT finding of circumferential sigmoid narrowing, elevated PSA (22.00), and detection of Shiga toxin-producing E. coli, while his hemodynamic stability (normal vital signs implied by labs) and mild anemia (Hb 10.1-11.4) allow for endoscopic evaluation rather than emergent angiography 1.

Laboratory Studies Already Completed

The workup is essentially complete based on the provided labs:

• Hemoglobin/Hematocrit monitoring: Already done (Hb 10.1-11.4 g/dL, Hct 30.1-34.4%) - shows mild anemia consistent with bleeding 2
• Coagulation assessment: PT/INR already checked (INR 1.2, slightly elevated) - critical for DOAC-treated patients 2
• Type and screen: Already completed (B positive, antibody screen negative) 2
• Renal function: Documented (Cr 1.40-1.68, eGFR 43-54) - important for DOAC dosing considerations
• Stool pathogen panel: Completed - Shiga toxin-producing E. coli detected, which can cause hemorrhagic colitis

Critical Imaging Finding Requiring Action

The CTA abdomen/pelvis already performed shows "apparent circumferential focal narrowing of the sigmoid colon" with recommendation for "direct visualization" - this is the key finding driving management 1, 3. This could represent:

• Malignancy (especially concerning given PSA 22.00)
• Ischemic stricture
• Inflammatory process
• Mass effect

Recommended Diagnostic Pathway

1. Urgent Colonoscopy (within 24 hours)

Perform full colonoscopy with anoscopy as the primary diagnostic and potentially therapeutic intervention 2. The 2019 British Society of Gastroenterology guidelines specifically recommend colonoscopy for major bleeds in stable patients 1. This patient is hemodynamically stable (no shock index >1 mentioned, normal labs suggest stable vital signs).

Rationale for colonoscopy priority:

• Direct visualization of the sigmoid narrowing identified on CT
• Ability to biopsy suspicious lesions (rule out malignancy given PSA 22.00)
• Therapeutic capability if bleeding source identified (cautery, clipping, injection)
• Evaluation for infectious colitis (Shiga toxin-positive) versus other pathology
• Assessment for diverticular bleeding (diverticulosis noted on CT)

2. No Additional Imaging Needed

The CTA is already complete and shows no active extravasation. Do not repeat CT or pursue angiography unless the patient becomes hemodynamically unstable (shock index >1) or shows evidence of ongoing massive bleeding 1, 3. The 2024 ACG/SAR consensus states CTA sensitivity is 85-90% for active bleeding, and this study was negative for active extravasation 3.

3. Upper Endoscopy Consideration

If colonoscopy does not identify a clear bleeding source, perform upper endoscopy 2. Up to 15% of patients with hematochezia have an upper GI source, particularly in anticoagulated patients 2.

Management of Anticoagulation

Critical Decision Point: DOAC Management

Temporarily hold the DOAC for colonoscopy 1. The 2019 BSG guidelines recommend interrupting anticoagulation at presentation for lower GI bleeding 1.

Timing considerations:

• Most DOACs have half-lives of 8-12 hours
• With eGFR 43-54 (CKD stage 3), clearance is prolonged
• Plan colonoscopy 24-48 hours after last DOAC dose if possible
• INR 1.2 suggests minimal residual effect currently

Do NOT reverse with prothrombin complex concentrate unless hemodynamically unstable, which this patient is not 1.

Transfusion Strategy

Use restrictive transfusion threshold (Hb <7 g/dL) given no documented cardiovascular disease history 1. Current Hb 10.1 g/dL does not require transfusion. The patient has blood typed and screened already.

If cardiovascular disease present: use Hb threshold <8 g/dL with target 8-10 g/dL 1.

Risk Stratification Context

This patient has multiple risk factors for major GI bleeding on anticoagulation 4:

• Age ≥70 years (70M)
• Male sex
• History of DVT (on anticoagulation)
• Renal insufficiency (eGFR 43-54)
• Anemia present

The 2022 RIETE registry data shows these patients have 0.89% risk of major GI bleeding during anticoagulation, with 33% mortality within 30 days of major GI bleeding 4.

Common Pitfalls to Avoid

1. Do not proceed to angiography without colonoscopy first - CTA shows no active bleeding, and the sigmoid narrowing requires tissue diagnosis 1

2. Do not discharge for outpatient workup - The Oakland score would likely be >8 given ongoing BRBPR, anemia, and concerning CT findings 1

3. Do not ignore the PSA 22.00 - This significantly elevated PSA with sigmoid narrowing raises concern for colorectal malignancy with possible prostatic involvement or separate prostatic pathology

4. Do not attribute bleeding solely to E. coli infection - While Shiga toxin-producing E. coli can cause hemorrhagic colitis, the sigmoid narrowing and elevated PSA suggest additional pathology requiring evaluation

5. Do not restart anticoagulation until bleeding source identified and controlled - Risk of VTE recurrence must be balanced against ongoing bleeding risk 4, 5

Additional Workup Based on Colonoscopy Findings

• If mass identified: Biopsy for histology, CEA already normal (2.7), consider urology referral for PSA 22.00
• If diverticular bleeding: Consider repeat colonoscopy if rebleeds, possible angiography with embolization 1
• If infectious colitis only: Supportive care, repeat stool cultures, consider antibiotics based on infectious disease consultation
• If ischemic colitis: Assess vascular supply, optimize hemodynamics, avoid NSAIDs

The inherited colorectal cancer panel is pending and may provide additional risk stratification 2.