Can hemoglobin (Hb) levels be low in patients with acute illness?

Hemoglobin Levels in Acute Illness

Yes, hemoglobin levels are commonly low in patients with acute illness, with approximately two-thirds of critically ill patients presenting with anemia on admission to intensive care units. 1 This anemia can develop rapidly and worsen during hospitalization due to multiple factors specific to acute illness.

Pathophysiology of Anemia in Acute Illness

Anemia in acute illness develops through several mechanisms:

1. Inflammation-mediated disturbances:

   • Blunted erythropoietic response to low hemoglobin 1
   • Inflammatory cytokines (TNF, IL-1, IL-6) suppressing erythropoiesis 1
   • Increased hepcidin leading to disturbed iron homeostasis 1, 2
   • Impaired erythropoiesis 2

2. Blood loss:

   • Excessive phlebotomy for diagnostic testing 1, 2
   • Ongoing blood loss from procedures 1
   • Occult bleeding 2

3. Other mechanisms:

   • Decreased red blood cell lifespan 1
   • Hemodilution from IV fluid administration 1, 2
   • Reduced erythropoiesis due to underlying disease states 1

Prevalence and Severity

The mean hemoglobin level on admission to critical care is approximately 11.0 g/dL 1. During hospitalization:

• More than 20% of septic patients have hemoglobin levels less than 10 g/dL on admission
• This rate doubles during the first week of sepsis 3
• Hemoglobin concentration on admission shows strong correlation with in-hospital mortality (OR 0.83,95% CI 0.74-0.92) 3

Management Considerations

Current guidelines recommend:

1. Restrictive transfusion strategy:

   • Transfuse only when hemoglobin decreases to <7.0 g/dL in most critically ill patients 1
   • Consider a higher threshold (Hb <8 g/dL) for patients with acute coronary syndromes or ischemic heart disease 2

2. Anemia prevention strategies:

   • Minimize phlebotomy by using small-volume tubes 1
   • Avoid standing orders for unnecessary blood tests 1
   • Use blood conservation devices 1
   • Appropriate management of medications causing anemia/bleeding 1

3. Non-transfusion management:

   • Erythropoietin may be beneficial in specific situations, especially after trauma 1
   • Iron therapy is generally not recommended except when used with erythropoietin 1

Clinical Implications

The presence of anemia in acute illness has important clinical implications:

• Anemia severity correlates with illness severity and length of stay 1
• Low hemoglobin on admission is an independent predictor of mortality in sepsis 3
• Anemia can persist long-term, with more than half of patients still anemic 6 months after discharge 1

Important Caveats

1. Sepsis significantly worsens outcomes: Sepsis is the strongest independent predictor of poor outcomes in severely anemic patients, even more than the hemoglobin level itself 4

2. Active bleeding compounds risk: Active bleeding is a significant predictor of poor outcomes, particularly when hemoglobin falls below 4.0 g/dL 4

3. Recovery timeline: Most patients with acute upper GI bleeding discharged with hemoglobin between 8-10 g/dL recover their hemoglobin levels within 45 days without complications 5

4. Diagnostic approach: When evaluating acute anemia in hospitalized patients, first rule out active bleeding as the most immediate life-threatening cause 2

In summary, anemia is an expected finding in acute illness due to multiple pathophysiological mechanisms. While it correlates with worse outcomes, current evidence supports a restrictive transfusion approach in most cases, with management focused on preventing further hemoglobin decline and addressing the underlying acute illness.