Chemical agents or substances that can prevent blood coagulation are called anticoagulants or anticoagulants, such as natural anticoagulants (heparin, hirudin, etc.), Ca2 + chelating agents (sodium citrate, potassium fluoride). Commonly used anticoagulants are heparin, EDTA, citrate, oxalate, etc. in practical application, we should choose according to different needs, in order to obtain the ideal effect. Their application characteristics are summarized as follows:
Heparin is the preferred anticoagulant for the detection of blood chemical composition. Heparin is a kind of mucopolysaccharide containing sulfate group, which is a kind of dispersive phase material with an average molecular weight of 15000. Its anticoagulant mechanism is mainly through the combination with antithrombin III to cause the change of antithrombin III configuration and accelerate the formation of thrombin thrombin complex to produce anticoagulant effect.
In addition, heparin can inhibit thrombin by plasma cofactor (heparin cofactor II). The commonly used heparin anticoagulants are sodium, potassium, lithium and ammonium salts of heparin, among which heparin lithium is the best, but its price is more expensive. Sodium and potassium salts will increase the content of sodium and potassium in blood, and ammonium salts will increase the content of urea nitrogen. The dosage of heparin anticoagulation is usually 10.0-12.5 IU / ml blood.
Heparin has less interference on blood components, does not affect the volume of red blood cells, and does not cause hemolysis. It is suitable for red blood cell permeability test, blood gas, plasma permeability, hematocrit and ordinary biochemical determination. However, heparin has antithrombin effect and is not suitable for hemagglutination test.
In addition, excessive heparin can cause leukocyte aggregation and thrombocytopenia, so it is not suitable for leukocyte classification and platelet count, let alone hemostasis test. In addition, heparin anticoagulant can not be used to make blood smear, because Wright staining appears dark blue background, which affects the production reduction of microscope. Heparin anticoagulant should be used in a short period of time, otherwise the blood can coagulate if it is placed too long.
2、 Ethylenediamine tetraacetate (EDTA salt)
EDTA can combine with Ca2 + in blood to form a chelate, the coagulation process is blocked, and the blood can not coagulate. EDTA salts include potassium, sodium and lithium. EDTA-K2 is recommended by the International Committee for standardization of Hematology, which has the highest solubility and the fastest anticoagulation speed. EDTA salt is usually prepared into 15% aqueous solution, adding 1.2mg EDTA per ml blood, that is, adding 0.04ml 15% EDTA per 5ml blood. EDTA salt can be dried at 100 ℃, and its anticoagulant effect remains unchanged.
The anticoagulant does not affect the count and size of white blood cells, has the least effect on the morphology of red blood cells, and can inhibit platelet aggregation, so it is suitable for general hematological detection. But if the concentration of anticoagulant is too high, the osmotic pressure will rise, which will cause cell shrinkage.
The pH of EDTA solution has a great relationship with salts, and low pH can make the cells expand. EDTA-K2 can slightly expand the volume of red blood cells, the average platelet volume is very unstable in a short time after blood collection, and tends to be stable after half an hour. EDTA-K2 can decrease Ca2 + and Mg2 +, and decrease creatine kinase and alkaline phosphatase. The optimal concentration of EDTA-K2 is 1.5mg/ml blood. If the blood is less, neutrophils will swell and disappear, platelets will swell and disintegrate, and normal platelet fragments will be produced, which makes the analysis results wrong.
Because EDTA can inhibit or interfere with the polymerization of fibrin monomer during fibrin clot formation, it is not suitable for the detection of blood coagulation and platelet function, nor for the determination of calcium, potassium, sodium and nitrogenous substances. In addition, EDTA can affect the activity of some enzymes and inhibit lupus erythematosus factor, so it is not suitable for making blood smear for histochemical staining and examination of lupus erythematosus cells.
Citrate is mainly sodium citrate. Its anticoagulant principle is that it can combine with Ca2 + in blood to form chelate, which makes Ca2 + lose coagulation function, and the coagulation process is blocked, so as to prevent blood coagulation. Sodium citrate has two kinds of crystals, na3c6h5o7 · 2H2O and 2na3c6h5o7 · 11h2o. The former is usually used to make 3.8% or 3.2% aqueous solution, which is mixed with blood according to the volume of 1:9.
Most coagulation tests can be anticoagulated with sodium citrate, which is helpful to the stability of factor V and factor VIII, and has little effect on mean platelet volume and other coagulation factors, so it can be used for platelet function analysis. Sodium citrate is one of the components of blood maintenance fluid in blood transfusion. However, sodium citrate 6mg can anticoagulate 1ml blood, strong alkaline, not suitable for blood tests and biochemical tests.
Oxalate is also a commonly used anticoagulant, which has the advantage of high solubility. Its principle of action is that the dissociated oxalate after dissolution forms calcium oxalate precipitation with Ca2 + in the sample, which makes Ca2 + lose the coagulation function and blocks the coagulation process.
The commonly used oxalate anticoagulants are sodium oxalate, potassium oxalate and ammonium oxalate. The concentration of sodium oxalate is 0.1 mol / L, and the ratio of sodium oxalate to blood is 1:9. However, high concentration of K + or Na + is easy to make the blood cells dehydrate and shrink, while ammonium oxalate can make the blood cells expand. Therefore, the anticoagulant with appropriate proportion of ammonium oxalate and potassium oxalate or sodium oxalate does not affect the shape and volume of red blood cells. It is often used in blood biochemical determination, but it is not suitable for the determination of K + and Ca2 +.
Due to the formation of calcium oxalate precipitation, red blood cells will appear serrated, white blood cells will appear vacuoles, lymphocytes and monocytes will be deformed, it is not appropriate to do blood test. Oxalate can cause platelet aggregation and affect the morphology of leukocytes, so it can not be used for the differential count of leukocytes and platelets.
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