In activity values

The concentration of heparin in tissues from which it is isolated is about 10-50 ppm. Hence, it is a trace substance. Further it combines easily with protein. Hence, its extraction from tissue economically has required considerable ingenuity. Methods for this involve the use of concentrated electrolyte solutions and proteolytic enzymes. Standards set for this compound do not appear to meet the problem presented in identifying this compound and this is responsible for the variability that occurs. This variability is important in standardizing heparin for clinical use [7, 8]. The variations seen in activity values by different tests indicate there are probably similar variations in activity of the preparations for different clinical uses - e.g. prevention of postoperative thrombosis, prevention of clotting in the heart-lung machine, etc. 

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