Synonyms: ALP isoenzymes
Related tests: total alkaline phosphatase
Clinical significance
This is an intracellular enzyme found in various tissues (liver, bone) in different isoforms, which the test can distinguish.
It is used to assess the percentage composition of the alkaline phosphatase fractions from the liver, bone and other tissues. The different isoenzymes derive either from different glycosylation of the same gene product (liver, bone, kidney) or from separate genes (intestinal, placental).
In the serum of a normal adult, the liver and bone fractions are present in roughly equal amounts.
In children and in people with high osteoblastic activity, the bone fraction predominates.
In liver disease the liver fraction increases and, in obstructive jaundice, so does the biliary fraction.
In pregnancy the placental isoenzyme is present, which is identical to a form expressed by some tumours (Regan isoenzyme).
Clinical indications
Further investigation when abnormal serum alkaline phosphatase values are found incidentally with no clinical suspicion.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.