a. The blood was not mixed in time.
b. Take blood with syringe. When injecting blood into the test tube, the blood volume exceeds the nominal blood volume of the test tube, resulting in excessive blood volume.
c. Insufficient anticoagulants cause coagulation.
d. Abnormal plug opening operation, that is, the anticoagulant of water agent is often adsorbed on the rubber plug. After abnormal plug opening, some anticoagulants will be brought out of the rubber plug, resulting in insufficient anticoagulant.
e. Experiments at home and abroad show that 11% of EDTA samples collected with syringe appear clot.