Normal ranges for alkaline phosphatase are 44 to 147 international units per liter of blood in adults, according to MedlinePlus. Normal levels of ALP in children are higher, and women typically have higher ALP ranges in the bloodstream, notes Mayo Clinic.
Male children at 4 years old have ALP ranges between 149 and 369 international units per liter, 10-year-olds normally have 191 to 435 international units per liter, and 15-year-old boys range from 138 to 511 international units per liter of blood, according to Mayo Clinic. Girls at 4 years old usually have 169 to 372 international units per liter of ALP, 10-year-olds have 215 to 476 international units per liter, and 15-year-old girls have 75 to 274 international units per liter of blood. ALP is a protein found in all tissues of the human body but mostly in the liver, bones, placenta and the intestines.
Higher-than-normal levels of ALP may indicate a bile duct obstruction in the liver, certain bone conditions and rapid bone growth during puberty, notes WebMD. High levels of ALP in the liver may be caused by jaundice, liver disease, liver damage and medicines that may affect liver function. Bone conditions relating to ALP levels include cancer that has spread to the bones, Paget's disease and vitamin D deficiency.