Blood hyperviscosity in acute and recent COVID-19 infection

BACKGROUND: Elevated estimated blood viscosity (EBV), derived from hematocrit and globulins, is associated with thrombotic complications, organ failure, and higher mortality in COVID-19 patients. Although informative, EBV does not account for cellular interactions or fibrinogen. OBJECTIVE: Investigate whether patients with acute and recent COVID-19 have altered whole blood viscosity (WBV) when measured at both high and low shear rates using in vitro blood samples from patients. METHODS: Cross-sectional study of 58 patients: 15 in the intensive care unit with acute COVID-19, 32 convalescent (9 < 8 weeks [W] from acute infection, 23 > 8 W), and 11 controls without COVID-19. WBV was measured at high (300 s(-1)) and low (5 s(-1)) shear rates (HSR, LSR) using a scanning capillary viscometer. RESULTS: Acute and convalescent patients<8W had mean WBV at LSR (16.0 centipoise [cP] and 15.1 cP) and HSR (5.1 cP and 4.7 cP). Mean WBV of convalescent>8W and control patients were 12.3 cP and 13.0 cP at LSR, and 4.1 cP and 4.2 cP at HSR. Acute and <8W patients had significantly higher WBV at both HSR and LSR compared to patients>8W (all p <= 0.01). No significant differences in WBV were observed between acute and <8W patients, or between patients >8W and controls. CONCLUSIONS: Hyperviscosity provides a possible explanation for thrombotic risk in acute and convalescent (<8W) patients. These findings have important implications for thromboprophylaxis.