Liver and pancreas
Alkalische fosfatase
An enzyme from the bile ducts and bone; raised when bile drainage is blocked or when bone formation is increased.
Everything about this testWhat it measures
Alkaline phosphatase (ALP) is an enzyme found mainly in the cells of the small bile ducts in the liver and in bone cells that make new bone. Smaller amounts come from the gut and, during pregnancy, from the placenta. The test measures the total of all these forms. A raised value can therefore come from the liver or from the bone; gamma-GT helps to make that distinction, because gamma-GT does rise with a bile duct problem and not with a bone cause.
- Blocked bile drainage (cholestasis) due to gallstones, a narrowing of the bile ducts or medicines
- Increased bone formation: a healing fracture, Paget's disease, severe vitamin D deficiency (osteomalacia)
- Liver disorders that mainly affect the bile ducts, such as primary biliary cholangitis
- Rarely: a tumor of the bile ducts or metastases in the bone
High
A raised alkaline phosphatase often has a harmless explanation. In children and teenagers, the value is normally much higher than in adults because of growth, in the second half of pregnancy the value rises because of the placenta, and in people with blood group O or B the value can be somewhat higher after a fatty meal. With a healing fracture, the value is raised for months. If gamma-GT is also raised, the cause lies in the liver or bile ducts: gallstones blocking the bile duct, medicines (including some antibiotics and anabolic steroids) or inflammation of the bile ducts. Symptoms are then pain in the upper right abdomen, itching, jaundice and dark urine. If gamma-GT is normal, the enzyme usually comes from the bone: with a vitamin D deficiency or Paget's disease; symptoms are then bone pain or an increased risk of fractures. Rarely: metastases in the bone.
Low
A low alkaline phosphatase is rare and usually has no significance. It occurs with malnutrition, a zinc or magnesium deficiency, an underactive thyroid and with anemia due to severe deficiencies. In exceptional cases, a very low value may point to hypophosphatasia, a rare inherited bone disorder.
Preparation
- Preferably do not eat for 12 hours before the sample is taken and drink only water. Also avoid an extra fatty meal the evening before: in some people the value is still higher the next morning after a fatty meal.
If your result is abnormal
The GP assesses alkaline phosphatase together with gamma-GT, bilirubin and ALAT. If the combination points to the liver or bile ducts, an ultrasound of the upper abdomen usually follows; if it points to the bone, vitamin D, calcium and phosphate are measured and, if needed, the bone form of the enzyme. A slightly raised value without symptoms is first repeated after a few weeks.
Reliability
Alkaline phosphatase points in a direction (liver or bone) but does not make a diagnosis. The value can only be interpreted together with gamma-GT, bilirubin and ALAT and with the person's age and situation. A slightly raised value in someone without symptoms is often temporary and, according to the Dutch GP guideline (NHG), is first repeated before any testing follows. With a persistently raised value and a normal gamma-GT, the laboratory can measure the bone form of the enzyme separately.
Limitations
- During growth (up to about 20 years of age) and in the second half of pregnancy, the value is normally raised; different reference values then apply.
- A fatty meal shortly before the sample collection can raise the value slightly, especially with blood group O and B; a fasting blood draw makes the result more reliable.
- A healing fracture or recent bone surgery raises the value for months.
- Medicines such as anti-epileptic drugs, some antibiotics and anabolic steroids can raise the value; reference values differ per laboratory.
How common is this
A slightly raised alkaline phosphatase without symptoms is fairly common and usually has a harmless cause. Gallstones, the most common serious cause of a raised value, occur in about 1 in 10 adults, more often in women and at older ages; most people with gallstones have no symptoms from them and a normal alkaline phosphatase. Paget's disease and bone metastases are rare.
Who is this useful for
Useful with symptoms that fit a bile duct problem (pain in the upper right abdomen, itching, jaundice), with bone pain or a suspected bone disorder, for monitoring a known liver or bone disease, and as part of a liver panel together with ALAT, gamma-GT and bilirubin. As a stand-alone test in healthy adults without symptoms, alkaline phosphatase has little value and a slightly raised result mainly leads to follow-up testing.
Downsides and risks
- A raised value due to growth, pregnancy or a healing fracture is easily mistaken for a liver or bone disease.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results