Some causes of elevated alkaline phosphatase include Paget disease, healing fractures, acromegaly, osteogenic sarcoma, liver or bone metastases, leukemia, myelofibrosis, rickets, osteomalacia, hypervitaminosis D , cholestasis of pregnancy, biliary obstruction, hyperthyroidism, infiltrative liver diseases (eg, sarcoid, TB, amyloidosis, abscess), cirrhosis, and myeloma.
Low levels may be found in hypophosphatasia, and less commonly in hypothyroidism .

References:

Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009 Dec;114(6):1326-31. PMID:19935037
Wallach, J. Interpretation of Diagnostic Tests, Eighth ed. Lippincott Williams & Wilkins, 2007 Fischbach FT, Dunning MB III, eds. A Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia, Lippincott Williams and Wilkins,2004