According to the color of the cranium, the venous vessels are mainly divided into the following types:

1. Green tube contains heparin lithium, heparin tube is generally used for biochemical and hemorheological detection, is the best choice for electrolyte detection. Because heparin causes white blood cell aggregation, it should not be used for white blood cell counting and classification.

2. The inner wall of red head tube is evenly coated with silica to prevent wall hanging, and coagulant is added at the same time. It is generally used for hepatitis virus, thyroid function, drug testing, AIDS testing, tumor markers and other serum immunological testing.

3. Purple head tubes contain ethylenediamine tetraacetic acid (EDTA) and its salt. EDTA salt is usually used as an anticoagulant. It is used for general hematological examination such as blood count and classification, and cannot be used for blood coagulation, trace elements and PCR examination.

4. The blue head tube contains sodium citrate, which is mainly used for the detection of fibrinolytic systems (prothrombin time, thrombin time, activated partial thrombin time, fibrinogen). When collecting blood, please pay attention to the collection of sufficient blood to prevent the cavity in the tube from affecting the accuracy of the test results. Immediately after blood collection, please reverse and mix for 5-8 times.

5. The blackhead tube contains sodium citrate, which is commonly used for the detection of ERYTHROcyte sedimentation rate. When the proportion of anticoagulant is too high, the blood is diluted and the ERYTHROcyte sedimentation rate can be accelerated.