Blood coagulation in vitro

Blood coagulation —In vitro platelet aggregation In vitro hemolysis... 

Fig. 4. Influence of 1-ethoxysilatrane on blood coagulation in vitro. Glass start (/), finish (J). Paraffin start (2), finish (4)...

The Hageman factor is a compound of unknown nature that is necessary for blood coagulation in vitro. Some patients lack this factor in the blood, but this does not usually lead to clinical symptoms. It is only responsible for retarded coagulation in vitro. Consequently, the disease is ordinarily discovered as an incidental finding during preoperative preparation of the patient. 

The blood clot formed in a test tube is strikingly different from a thrombus deposit formed in vivo in the vascular system. A clot in a test tube consists of a fibrin network in which red cells, white cells, and relatively small numbers of platelets are found. On the other hand, an in vivo thrombus deposit consists of large amorphous masses of platelets, surrounded by white cells with a few red cells. However, it is possible to form deposits closer to thrombi rather than to blood clots in vitro by using circulating plastic loops in which the blood is in motion during coagulation. ... 

In Vitro Anticoagulants. A number of substances have been identified that prevent coagulation of the blood when it is removed from the vascular compartment of the body. Most of these substances remove a vital constituent of the blood that is essential in the mediation of transformation of hquid blood into a soHd. 

Many of the coagulation factors measured by global coagulation tests have limited stability, and the time and temperature of storage of sample will affect their measurements. Concepts of analyte stability and half-life in plasma extend to markers measured by immunoassay. Markers of platelet activation are affected by artifactual activation in vitro upon collection of the blood specimen. This section will highlight some of the nonanalytical variables that, if uncontrolled, can lead to spurious results and thus affect the interpretation of laboratory data. 

Bagdy D., Barabas E., Bajusz S., Szell E. In vitro inhibition of blood coagulation by tripeptide aldehydes A retrospective screening study focused on the stable D-MePhe-Pro-Atg-H-H2S04. Thromb Haemost 1992 67,325-30. 

Warfitrin and dicoumaroi prevent coagulation only in vivo and cannot prevent coagulation of blood in vitro (drawn from a patient into a test tube). 

L B. Warfarin does not produce an anticoagulant effect in vitro. It inhibits coagulation of blood only in vivo, because the effect depends upon warfarin s effect in the liver on the production of clotting factors. Warfarin does not require conversion into an active drug. It inhibits the post-ribosomal carboxy-lation of glutamic acid residues in the vitamin K-dependent clotting factors. Therefore, heparin rather than warfarin is used when blood is collected from donors and stored. 

Early observations showed that blood clotted faster in clean glass tubes than in siliconized glass. When Mr. Hageman s blood failed to clot in vitro, it was speculated that a Hageman Factor was responsible for the in vitro activation of blood coagulation (see Ref. 2) for a delightful account). 

Greenberg, C. S., Miraglia, C. C., Rickies, F. R., and Shuman, M. A. (1985). Cleavage of blood coagulation factor XIII and fibrinogen by thrombin during in vitro clotting. J. Clin. Invest. 75, 1463—1470. 

An important step in the blood coagulation pathway is the formation of the prothrombinase complex. The latter is a mixture of factor V, factor Xa, Ca2+, and phospholipid. In this case, a phospholipid mixture with a net negative charge will allow the prothrombinase complex to form. This active enzyme is important in cleaving prothrombin to yield thrombin. The most active phospholipid mixture for in vitro studies has proven to be phosphatidylserine-phosphatidylcholine. Subsequently the hypothesis has developed that phosphatidylserine is key to the formation of prothrombinase. 

Chandler AB (1958) In vitro thrombotic coagulation of the blood. A method for producing a thrombus. Lab Invest 7 110-114... 

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