Summary Sickle cell disease (SCD) includes a group of heterogenous disorders that result in significant morbidities. HbSS is the most common type of SCD and HbSC is the second most common type of SCD. The prevalence of HbSC disease in the United States and United Kingdom is ~1 in 7174 births and 1 in 6174 births respectively. Despite its frequency, however, HbSC disease has been insufficiently studied and was historically categorized as a more ‘mild’ form of SCD. We conducted this study of HbSC disease as part of the NHLBI funded Sickle Cell Disease Implementation Consortium (SCDIC). The SCDIC registry included 2282 individuals with SCD, ages 15–45 years of whom 502 (22%) had HbSC disease. Compared with people with sickle cell anaemia (SCA), the study found that people with HbSC disease had a higher frequency of splenomegaly ( n (%) = 169 (33.7) vs. 392 (22.1)) and retinopathy ( n (%) = 116 (23.1) vs. 189 (10.6)). A Many people with HbSC also had avascular necrosis ( n (%) = 112 (22.3)), pulmonary embolism ( n (%) = 43 (8.6)) and acute chest syndrome ( n (%) = 228 (45.4)) demonstrating significant disease severity. HbSC disease is more clinically severe than was previously recognized and deserves additional evaluation and targeted treatments.

The clinical spectrum of HbSC sickle cell disease‐not a benign condition