blood enzyme activity level serum alkaline phosphatase activity level 2011-11-02T04:11:05Z Quantitation of the catalytic effect exerted by alkaline phosphatase (AP) in a specified sample of serum, the clear liquid that separates from blood after it has clotted completely, i.e. blood plasma from which fibrinogen has been removed. AP is an enzyme that catalyzes the cleavage of orthophosphate from orthophosphoric monoesters under alkaline conditions. mshimoyama