Hemoglobin and Hematocrit in Hemolysis
Yes, hemoglobin and hematocrit are typically low in patients experiencing hemolysis, as the destruction of red blood cells leads to anemia with sustained reticulocytosis in the absence of blood loss. 1
Pathophysiology and Laboratory Findings
Hemolysis causes anemia through two primary mechanisms that both result in decreased hemoglobin and hematocrit levels 1:
- Intravascular hemolysis occurs when erythrocytes lyse directly in the circulation due to complement fixation, trauma, or other extrinsic factors, leading to immediate release of hemoglobin into plasma 1
- Extravascular hemolysis (most common) occurs when red cells are removed by the mononuclear-phagocytic system due to intrinsic defects or bound immunoglobulins 1
Diagnostic Laboratory Pattern
The diagnosis of hemolysis is established by the presence of anemia with sustained reticulocytosis in the absence of blood loss 1. Additional confirmatory findings include:
- Increased unconjugated bilirubin and LDH 1
- Decreased haptoglobin and hemopexin 1
- Marrow erythroid hyperplasia 1
- Increased free hemoglobin 1
- Decreased 51Cr red cell half-life 1
Severe Intravascular Hemolysis
In cases of severe and rapid intravascular hemolysis, additional findings appear 1:
Conditions causing significant intravascular lysis include incompatible transfusion, G6PD deficiency, paroxysmal nocturnal hemoglobinuria (PNH), severe burns, and certain infections 1.
Special Context: Hyperhemolysis in Sickle Cell Disease
In patients with sickle cell disease, hyperhemolysis represents an extreme form where hemoglobin drops below pretransfusion levels, indicating clearance of both transfused and the patient's own red cells 2. This life-threatening condition requires:
- Serial monitoring of hemoglobin, hematocrit, HbA and HbS fractions, reticulocyte count, bilirubin, LDH, and urinalysis for hemoglobinuria 2
- Avoidance of further transfusion unless life-threatening anemia exists, as additional transfusions may worsen hemolysis and induce multiorgan failure and death 2
- Consideration of immunosuppressive therapy (IVIg, high-dose steroids, eculizumab, or rituximab) for ongoing hyperhemolysis 2
Important Clinical Caveat
Red cell morphology is abnormal in almost all cases of hemolytic anemia, and in certain cases can be diagnostic of the underlying condition 1. Treatment is primarily supportive with therapy directed at the underlying cause of hemolysis 1.