Exposure to cold temperatures and high altitudes can precipitate a sickle cell crisis primarily due to which mechanism?

• A. Increased red blood cell production
• B. Thickening of the blood due to higher viscosity
• C. Decreased oxygen affinity of hemoglobin
• D. Immune suppression

Answer: (B)

Exposure to cold and high altitude precipitates a sickle cell crisis because these conditions promote deoxygenation and reduce flow in small vessels, which drives HbS to polymerize and the red blood cells to sickle. When HbS loses oxygen, it tends to polymerize, turning RBCs rigid and misshapen. Those deformed cells are less able to navigate the microcirculation, which makes the blood more viscous and slows flow. Cold causes vasoconstriction, further decreasing perfusion, while high altitude lowers ambient oxygen, increasing arterial deoxygenation. The combination leads to thicker, sluggish blood that readily occludes small vessels, producing the vaso-occlusive crisis characteristic of sickle cell disease.