A chromogenic kit or the quantitative determination of unfractionated heparin (UF Heparin) or low molecular weight heparin (LMW Heparin) in human citrated plasma using automated and microplate methods.Heparin is the most frequently used antithrombotic therapeutic. The biological activity of this sulfated glycosaminoglycan resides in its ability to accelerate (up to 2000-fold) the inhibitory effect of antithrombin (AT) on the coagulation proteases. The amount of LMW Heparin or UF Heparin is determined from the anti-FXa activity expressed by the [AT · Heparin] complex formed in plasma.