What is alkaline phosphatase?

Alkaline phosphatase is an enzyme that removes phosphates from various molecules in the body, including proteins and alkaloids. While alkaline phosphatase is present throughout the body, the highest concentrations are found in the kidneys, bones, liver, placenta and bile duct. If high levels are noted in blood tests, it could mean there is a blockage of the bile duct. This blood test is often ordered as part of a liver health screening.

Normal Value Range

• Negative Pregnancy Adult: 33 to 96 U/L or 0.55 to 1.6 µkat/L
• Pregnancy Trimester One: 17 to 88 U/L or 0.28 to 1.47 µkat/L
• Pregnancy Trimester Two: 25 to 126 U/L or 0.43 to 2.1 µkat/L
• Pregnancy Trimester Three: 38 to 229 U/L or 0.63 to 3.82 µkat/L

If alkaline phosphatase is higher than normal values the patient may have healing fractures, Paget disease, acromegaly, liver metastases, bone metastases, osteogenic sarcoma, leukemia, rickets, myelofibrosis, osteomalacia, biliary obstruction, pregnancy cholestasis, hypervitaminosis D, hyperthyroidism, cirrhosis, liver diseases (infiltrative), or myeloma.

If alkaline phosphatase is lower than normal hypophosphatasia may be the cause. Low levels are found less often in women with hypothyroidism.