Why is it important to check hemoglobin levels in patients with sickle cell disease, particularly those of African, Mediterranean, or Middle Eastern descent?

Why Check Hemoglobin in Sickle Cell Disease

Hemoglobin monitoring is essential in sickle cell disease because it defines disease severity, guides transfusion decisions, monitors treatment effectiveness, and helps predict perioperative risk—with baseline levels varying dramatically by genotype from 60-90 g/L in severe HbSS disease to near-normal levels in milder variants. 1

Disease Severity Assessment and Baseline Characterization

• Hemoglobin levels directly correlate with disease phenotype and severity. Patients with HbSS (sickle cell anemia), HbSβ0-thalassemia, and HbSD disease have severe anemia with typical baseline hemoglobin of 60-90 g/L, while those with HbSC disease typically maintain higher levels and experience fewer symptoms. 1, 2

• Chronic hemolytic anemia is a defining feature of sickle cell disease. The continuous cycle of sickling and un-sickling causes red cell membrane damage, formation of irreversibly sickled cells, and ongoing hemolysis by the reticuloendothelial system. 1

• Knowing the patient's baseline hemoglobin is critical for detecting acute complications. A drop from baseline can indicate aplastic crisis (commonly from parvovirus B19), acute splenic sequestration (with hemoglobin falling to 10-30 g/L), or hyperhemolysis. 1, 2

Transfusion Management and Safety

• Hemoglobin measurement determines when transfusion is indicated and sets the target. When transfusion is needed, the target hemoglobin is 100 g/L. 2

• Exceeding hemoglobin thresholds above 100 g/L increases viscosity-related complications. This is particularly important in HbSC disease, where baseline hemoglobin is already higher and exchange transfusion rather than simple transfusion may be required. 2, 3

• Serial hemoglobin monitoring tracks transfusion effectiveness and prevents over-transfusion. This is especially critical given that all transfusions must be HbS-negative with extended phenotype matching to prevent alloimmunization. 2

Treatment Monitoring

• Hemoglobin levels assess response to hydroxyurea therapy. Hydroxyurea increases fetal hemoglobin (HbF) levels, which reduces sickling—patients with HbF >8% have milder disease with fewer symptoms. 1, 2

• Quantifying the percentage of HbS versus HbF or transfused HbA is essential for monitoring disease-modifying therapies. This requires hemoglobin electrophoresis or similar methods, not just total hemoglobin measurement. 4

Perioperative Risk Stratification

• Preoperative hemoglobin assessment is mandatory for surgical planning. Patients with sickle cell disease are at increased risk of perioperative complications including acute chest syndrome, stroke, acute renal insufficiency, and painful crises—with the majority occurring postoperatively. 1, 2

• Genotype-specific hemoglobin levels guide perioperative transfusion decisions. HbSS patients with their severe baseline anemia (60-90 g/L) require the most aggressive preventive measures and have the highest complication rates. 2, 5

• The nominated lead haematologist uses hemoglobin levels to determine the perioperative transfusion plan. This must be decided before elective surgery, and patients should be scheduled early on the operating list to avoid prolonged starvation that could worsen anemia. 1, 2

Detection of Acute Complications

• Hemoglobin monitoring identifies life-threatening acute events. Acute splenic sequestration crisis in young children (5 months to 2 years) presents with massive splenomegaly and acute anemia with hemoglobin dropping to 10-30 g/L, requiring immediate intervention. 1

• Aplastic crisis causes profound anemia over 5-10 days. Recognition requires knowing the patient's baseline hemoglobin to detect the acute drop. 1

• Suspected hyperhemolysis requires immediate hemoglobin assessment. If hyperhemolysis is present, additional transfusions should be avoided unless life-threatening anemia exists, as further transfusion may paradoxically worsen hemolysis. 2

Common Pitfalls to Avoid

• Never rely on a single hemoglobin value without knowing the patient's baseline. What appears "acceptable" (e.g., 90 g/L) may represent a dangerous acute drop for an HbSC patient whose baseline is 110 g/L. 1, 6

• Do not use rapid sickle solubility tests alone for diagnosis or monitoring. These tests cannot differentiate between heterozygous, compound heterozygous, or homozygous states, and give false negatives in neonates or heavily transfused patients. Full hemoglobinopathy screening with electrophoresis is required. 1

• Avoid aggressive transfusion to "normalize" hemoglobin levels. The target is 100 g/L when indicated, not higher, due to viscosity-related complications. 2, 3