Hemoglobin SS Disease is a Specific Form of Sickle Cell Disease
Hemoglobin SS disease (also called sickle cell anemia) is not the same as sickle cell disease overall—rather, it is the most common and severe subtype within the broader category of sickle cell disease. 1
Understanding the Terminology
Sickle cell disease is an umbrella term that encompasses multiple genetic variants, all characterized by the presence of abnormal hemoglobin S (HbS) that causes red blood cells to sickle. 1 The term "sickle cell disease" includes:
Major Genotypes of Sickle Cell Disease:
Hemoglobin SS (HbSS) - also called "sickle cell anemia": The homozygous form where both beta-globin genes carry the sickle mutation, representing 50-60% of all sickle cell disease cases in the UK 1
Hemoglobin SC (HbSC) disease: A compound heterozygous state with one sickle gene and one hemoglobin C gene, accounting for 25-30% of cases and typically presenting with moderate severity 1
Sickle β⁰-thalassemia (HbS β⁰ thal): Severe form accounting for 1-3% of cases 1
Sickle β⁺-thalassemia (HbS β⁺ thal): Milder form accounting for 5-10% of cases 1
Other sickle variants (HbSD, HbSE, HbSO-Arab): Variable severity, accounting for 1-2% of cases 1
Clinical Significance of the Distinction
HbSS disease represents the most severe phenotype within sickle cell disease, characterized by:
- Severe anemia with typical hemoglobin levels of 60-90 g/L (6-9 g/dL) 1
- Early onset of painful crises 1
- 80-95% HbS with no normal adult hemoglobin (HbA) present 1
- Higher risk of complications including stroke, acute chest syndrome, and end-organ damage 1, 2
In contrast, other forms like HbSC disease typically have higher baseline hemoglobin levels and generally fewer symptoms, though they still require careful management. 1
Practical Clinical Implications
When encountering the term "sickle cell disease" in clinical practice:
- Always determine the specific genotype (HbSS, HbSC, HbS β-thal, etc.) as this directly impacts disease severity and management 1
- HbSS patients require the most aggressive preventive measures perioperatively and have the highest complication rates 1
- All forms of sickle cell disease share the common pathophysiology of HbS polymerization causing vaso-occlusion, hemolysis, and end-organ damage 1, 2
Common Pitfall to Avoid
Do not confuse sickle cell disease with sickle cell trait (HbAS), which is a benign carrier state affecting 55-65% HbA and 30-40% HbS, and only becomes clinically relevant at extremes of physiology. 1 Sickle cell trait does not cause the chronic complications seen in sickle cell disease and requires no routine treatment. 1