Serum alkaline phosphatase can show the macro-enzyme phenomenon.
Usual presentation: persistent elevation of serum alkaline phosphatase activity without identifiable cause.
Pathogenesis: The usual mechanism is a complex of the alkaline phosphatase with an immunoglobulin, usually IgG. This results in decreased clearance of the alkaline phosphatase activity and a longer half-life.
Situations where macro-alkaline phosphatase has been reported:
(1) monoclonal proteinemia (MGUS, myeloma)
(2) pancreatitis
(3) hepatocellular carcinoma
The presence of an alkaline phosphatase complex with IgG can be demonstrated by polyethylene glycol precipitation with gel filtration and immunoelectropheresis.
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