why does chelatin of calcium prevent blood clotting?

why does chelatin of calcium prevent blood clotting?
chelation of calcium prevents clotting because calcium ions are required to convert fibrinogen to fibrin
Calcium is in the adjectives pathway of the coagulation cascade.
Sodium Citrate is the anticoagulant within that blue top tube that Coagulation tests such as PT (extrinsic factor) and aPTT (instrinsic factor) are perform out of.
The sodium citrate chelates the Ca++ and halts the tip out of the coagulation cascade.
When the test are performed, one of the reagents on the analyzer is Calcium Chloride (CaCl2). In the armour of the aPTT test, a Phospholipid and CaCl2 is added to the citrated plasma to restart, if you will, the coagulation deluge. Time is measured in second how quickly clot formation is formed.
For the PT, Thromboplastin is added to the preview. Time again measured in second, how quickly the clot forms.