The Hyperviscosity Paradox In Haemoglobin SC Disease: A Cross-Sectional Study In South-West Nigeria
Keywords:
Blood viscosity, Fibrinogen, Haematocrit, Haemoglobin SC disease, Haemorheology, NigeriaAbstract
Haemoglobin SC (HbSC) disease is often regarded as a milder sickle syndrome than homozygous HbSS because routine coagulation indices and haematocrit are less deranged, but whether this perceived mildness extends to blood rheology is unclear. In this cross-sectional, phenotype-stratified sub-analysis of a larger haemostasis–haemorheology cohort recruited from two tertiary-hospital sickle cell clinics in South-West Nigeria, whole blood viscosity (WBV), plasma viscosity, packed cell volume (PCV) and fibrinogen were compared across haemoglobin AA (HbAA, n=74), HbSS steady-state (n=69) and HbSC (n=10) participants. WBV and plasma viscosity were measured by capillary-tube viscometry, fibrinogen by the gravimetric clot-weight method, and phenotype by microchip electrophoresis. As participant-level data were unavailable, HbSC-versus-HbAA comparisons used Welch's t-test computed from reported group means, standard deviations and sample sizes. PCV was 21.0% lower in HbSC than HbAA (33.8±2.8% vs 42.8±2.3%; p<0.001), yet WBV was 12.1% higher (4.83±0.27 vs 4.31±0.21 mPa·s; mean difference 0.52, 95% CI 0.32–0.72; p<0.001) and only 4.0% below the HbSS-steady value. The viscosity-to-haematocrit ratio was 41.6% higher in HbSC than HbAA. Fibrinogen was 25.8% higher in HbSC than HbAA (3.9±0.5 vs 3.1±0.3 g/L; p<0.001), while prothrombin time and activated partial thromboplastin time in HbSC remained closer to HbAA than to HbSS-steady values. Despite a haematocrit closer to normal than HbSS, HbSC disease shows whole blood viscosity approaching HbSS steady-state values, with disproportionately elevated fibrinogen, a rheological burden that routine coagulation screening and haematocrit may fail to detect.
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