What labs should be ordered for a patient presenting with a gastrointestinal (GI) bleed?

Laboratory Tests for Gastrointestinal Bleeding

Order a complete blood count (CBC), basic metabolic panel (BMP), coagulation studies (PT/INR), liver function tests, and type and crossmatch for all patients presenting with GI bleeding. 1, 2

Essential Laboratory Panel

Core Tests Required for All Patients

• Complete Blood Count (CBC): Obtain hemoglobin and hematocrit to assess bleeding severity and guide transfusion decisions 1, 2

  • Use hemoglobin <7 g/dL as transfusion threshold for most patients (target 7-9 g/dL) 1, 3
  • Use hemoglobin <8 g/dL as threshold for patients with cardiovascular disease (target ≥10 g/dL) 1, 3
  • Hemoglobin <8 g/dL increases likelihood of severe bleeding requiring urgent intervention (LR 4.5-6.2) 4

• Coagulation Panel (PT/INR): Evaluate for coagulopathy that may contribute to bleeding 1

  • Correct INR >1.5 with prothrombin complex concentrate and vitamin K if patient is unstable 1, 3
  • Elevated PT increases risk of adverse outcomes 5

• Basic Metabolic Panel: Calculate BUN/creatinine ratio 2, 4

  • BUN:creatinine ratio >30 strongly suggests upper GI bleeding (LR 7.5) 4
  • Assess renal function before contrast studies 1

• Type and Crossmatch: Essential for patients with severe bleeding or hemodynamic instability to enable rapid transfusion 1

Additional Tests Based on Clinical Context

• Liver Function Tests: Include in initial workup for suspected variceal bleeding or patients with known liver disease 1, 6

• Platelet Count: Transfuse platelets if <50,000/µL in actively bleeding patients 5

Risk Stratification Using Laboratory Values

Oakland Score Components (for Lower GI Bleeding)

The Oakland score incorporates hemoglobin as a critical variable for risk stratification 7:

• Hemoglobin <70 g/L: 22 points
• Hemoglobin 70-89 g/L: 17 points
• Hemoglobin 90-109 g/L: 13 points
• Hemoglobin 110-129 g/L: 8 points
• Hemoglobin 130-159 g/L: 4 points
• Hemoglobin ≥160 g/L: 0 points

Oakland score ≤8 indicates safe discharge for outpatient investigation; score >8 requires hospital admission 7, 5

Shock Index Calculation

• Calculate shock index (heart rate ÷ systolic blood pressure) at presentation 7, 1, 3
• Shock index >1 indicates hemodynamic instability requiring urgent intervention including immediate CT angiography 1, 3, 5

Common Pitfalls to Avoid

• Do not delay laboratory testing while waiting for endoscopy—obtain blood work immediately upon presentation 1, 2

• Do not rely solely on initial hemoglobin as it may not reflect acute blood loss; serial measurements are necessary 2

• Do not forget to check coagulation studies even in patients without known bleeding disorders, as unrecognized coagulopathy significantly impacts management 1, 5

• Always calculate BUN:creatinine ratio to help differentiate upper from lower GI bleeding, as this simple calculation has strong diagnostic value (LR 7.5 for upper GI source) 4