What is the initial step in evaluating acute anemia in hospitalized patients?

Differential Diagnosis and Initial Evaluation of Acute Anemia in Hospitalized Patients

The first step in evaluating acute anemia in hospitalized patients is to rule out active bleeding, as this represents the most immediate life-threatening cause requiring urgent intervention. 1

Initial Assessment Algorithm

1. Assess for hemodynamic instability

   • Vital signs (tachycardia, hypotension)
   • Signs of tissue hypoperfusion
   • Mental status changes

2. Evaluate for active bleeding

   • Visible blood loss (hematemesis, melena, hematochezia)
   • Hidden blood loss (retroperitoneal, intracranial, intra-abdominal)
   • Iatrogenic blood loss (phlebotomy, procedures)

3. Review hemoglobin trend

   • Rate of decline (acute vs. gradual)
   • Previous baseline hemoglobin
   • Daily drop of approximately 0.5 g/dL is common in ICU patients 1

Key Diagnostic Categories

Active Hemorrhage

• GI bleeding: Most common source of acute blood loss in hospitalized patients

  • Consider NGT lavage in ventilated patients to confirm upper GI source 1
  • Document bleeding with photographs when possible 1
  • Consider prothrombotic state in COVID-19 patients on anticoagulants 1

• Procedure-related bleeding:

  • Recent surgeries, invasive procedures
  • Vascular access complications

• Occult bleeding:

  • Retroperitoneal hemorrhage (especially in anticoagulated patients)
  • Intramuscular bleeding

Non-Hemorrhagic Causes

• Iatrogenic hemodilution:

  • Excessive IV fluid administration
  • Consider diagnostic phlebotomy reduction strategies 1

• Hemolysis:

  • Mechanical (ECMO, VAD, prosthetic valves)
  • Medication-induced
  • Transfusion reactions
  • Autoimmune processes

• Critical illness-related anemia:

  • Inflammation-mediated (disturbed iron homeostasis, impaired erythropoiesis)
  • Reduced red cell survival 1

Diagnostic Workup

Initial Laboratory Tests

• Complete blood count with indices
• Reticulocyte count
• Peripheral blood smear
• Coagulation studies
• Iron studies (ferritin, transferrin saturation)
• Hemolysis markers (LDH, haptoglobin, bilirubin)

Classification by MCV

• Microcytic anemia (MCV < 80 fL):

  • Iron deficiency (ferritin <100 μg/L, TSAT <20%)
  • Thalassemia
  • Anemia of inflammation 1, 2

• Normocytic anemia (MCV 80-100 fL):

  • Acute blood loss
  • Anemia of inflammation/critical illness
  • Renal insufficiency 1

• Macrocytic anemia (MCV >100 fL):

  • B12/folate deficiency
  • Medication effect
  • Liver disease 1

Management Considerations

Transfusion Thresholds

• Restrictive strategy (Hb <7 g/dL) recommended for most critically ill patients 1
• Consider higher threshold (Hb <8 g/dL) for:
  • Acute coronary syndromes
  • Ischemic heart disease 1, 2
• Single-unit transfusion policy when possible 1

Non-Transfusion Management

• Bleeding control:

  • Endoscopic, surgical, or interventional radiology for active bleeding
  • Tranexamic acid for trauma-related bleeding within 3 hours 1

• Erythropoiesis support:

  • Erythropoietin may be beneficial, especially after trauma 1
  • Iron therapy only recommended in conjunction with erythropoietin 1

Common Pitfalls to Avoid

• Overlooking iatrogenic causes: Phlebotomy can contribute significantly to anemia in hospitalized patients
• Normalizing blood pressure during active hemorrhage: Maintain lower acceptable BP until hemorrhage is controlled 1
• Excessive transfusion: Transfuse only to relieve symptoms or reach safe Hb levels (7-8 g/dL) 2
• Missing occult bleeding: Consider CT angiography when endoscopy is not immediately available 1
• Neglecting non-bleeding causes: Critical illness itself causes anemia through inflammation, reduced erythropoiesis, and shortened RBC lifespan 1

By following this systematic approach, clinicians can efficiently identify and address the cause of acute anemia in hospitalized patients, prioritizing life-threatening conditions while avoiding unnecessary interventions.