ALP (alkaline phosphatase) is an enzyme occurs mainly in liver cells near the bile ducts but is also present in bone. ALP is often measured as part of a routine liver profile test or may be requested with several other tests if a patient has symptoms of a liver, gallbladder, or bone disorder.
The ALP test can be helpful in identifying conditions such as hepatitis (inflammation or infection of the liver), cirrhosis (scarring of the liver), inflammation of the gallbladder or blockage of bile ducts. You may also need an ALP test if you are taking a medication that has the potential to damage your liver.
If the clinical symptoms of liver disease are present, or if other liver blood test results are raised, high ALP levels usually indicate the source is the liver. ALP is also increased when there is any obstruction to the bile ducts such as gallstones and is usually increased before the physical symptoms of jaundice occur.
As ALP is not liver specific, it can also be measured as part of a bone profile test. If other bone markers such as calcium and are abnormal this suggests the raised ALP is from bone. This can indicate the presence of bone disorders such as rickets due to a deficiency of calcium, phosphate or vitamin D, hyperparathyroidism, or osteomalacia where there is softening of the bones due to vitamin D deficiency.
ALP can also be raised during pregnancy and children also have higher ALP levels because their bones are growing, in particular during puberty. ALP can be slightly raised for a few hours after eating so the test should ideally be performed after fasting overnight.
Lower than normal ALP levels in your blood is rare, but can indicate malnutrition, which could be caused by celiac disease or a deficiency in vitamins and minerals.