What might cause unexpected clotting in an anticoagulated blood tube?

Insufficient mixing of an anticoagulated blood tube can lead to unexpected clotting because the anticoagulants need to be evenly distributed throughout the blood sample to effectively prevent coagulation. When blood is drawn into a tube containing an anticoagulant, it is essential to mix the blood thoroughly with the additive to ensure that the anticoagulant interacts with all components of the blood. Failing to mix the blood adequately can result in areas where the anticoagulant is not present, allowing clotting factors to work unchecked and leading to the formation of clots.

While excessive shaking may cause hemolysis and affect sample integrity, it is not typically a direct cause of clot formation. Delayed processing can also lead to clotting, but this generally occurs due to prolonged exposure of the sample to the body's temperature and factors that can initiate the clotting cascade, not because of the immediate mixing process. Low temperature might affect the overall viscosity of the blood or other properties but is less likely to be the reason for unexpected clots in an anticoagulated tube compared to mixing issues.