Alkaline phosphatase (ALPP) is plasma membrane bound glycoprotein involved in energy production. Human ALKP is classified into four tissue specific forms or isozymes, according to the site where it is expressed: placenta, intestine, liver, bone, kidney and germ cell. During pregnancy, serum ALPP levels increase progressively, reaching its highest value in the third trimester, mostly due to addition of placental isoenzyme. This usually results in doubling in the total ALPP level.