Alkaline phosphatase is an enzyme (protein) produced by several body tissues, including the bones, liver (bile ducts), intestine and placenta. High alkaline phosphatase levels in the blood can have different causes but are usually due to a liver disorder or increased activity of the bone cells.
An increase in the levels of other markers for liver disease (bilirubin, ALT, AST, GGT) indicates that the high alkaline phosphatase levels are most likely due to a liver disease (hepatitis, stones or other blockages of the bile ducts, etc.).
If no abnormality is found in the other markers for liver disease, particularly if there is also an abnormal calcium or phosphorus level, a high alkaline phosphatase level indicates accelerated bone metabolism. The highest levels (10 to 25 times the normal) are found in Paget’s disease, a condition causing painful bone deformation. Extremely high levels are also found in certain types of bone cancer. Moderately high levels are seen in osteomalacia in adults or rickets in children (Vitamin D deficiency). Higher alkaline phosphatase levels are normal during growth or bone fracture repair, and in late pregnancy (additional phosphatase alkaline coming from the placenta).