Alkaline phosphatase (ALP)
Enzyme from liver, bile ducts and bone, part of liver and bone panels
Also known as
Definition
Alkaline phosphatase (ALP) is an enzyme found in all body tissues, with higher amounts in the liver, bile ducts and bones. Each of these tissues makes its own form (isoenzyme). The standard test shows the total amount in the blood but not which tissue it comes from. That is why ALP is usually assessed together with other liver values or bone markers.
| Parameter | Value |
|---|---|
| Unit | U/l (µkat/l) |
| Reference Range | Adults: 40–129 U/l (0.67–2.15 µkat/l). The range depends on age, sex and lab method; growing children and teens as well as pregnant women have higher values. Labs differ; the range printed on your report is what counts, and your doctor interprets the result. |
Agree on your personal target range with your doctor.
Conversion: 1 U/l ≈ 0.0167 µkat/l; 1 µkat/l = 60 U/l.
↓ What a low value means
Low values are less common. They can be related to zinc deficiency, protein deficiency or malnutrition, pernicious anemia, thyroid disease, Wilson disease or the rare inherited condition hypophosphatasia. Birth control pills and certain medicines can also lower ALP. Discuss any deviation with your doctor.
↑ What a high value means
Elevated values can come from the liver or from bone. If other liver values are also elevated, the liver is the more likely source, for example with blocked bile ducts, hepatitis or cirrhosis. If liver values are normal, bone conditions such as Paget disease or osteomalacia, a healing fracture or an overactive parathyroid may be behind it. Growth, pregnancy and a fatty meal before the blood draw can also raise the value. An isoenzyme test can show which tissue the ALP comes from. Discuss any deviation with your doctor.
When to test
ALP is often part of a routine checkup, a liver panel or a comprehensive metabolic panel. It is measured specifically when symptoms point to the liver or bile ducts (such as yellowing of skin and eyes, dark urine, pale stool, itching) or with bone pain and fractures. Because it is often drawn with other values, fasting for several hours may be required.
Frequently asked questions
Can ALP be elevated without any disease? +
Yes. ALP is higher in growing children and teens and during pregnancy. According to MedlinePlus, an elevated value is also possible without a condition that needs treatment; it is always interpreted together with symptoms, medical history and other values.
How can you tell whether ALP comes from the liver or from bone? +
The standard test only shows the total amount. Other liver values give a clue: if they are also elevated, the liver is the more likely source. An ALP isoenzyme test is more precise but is not available everywhere.
Do I need to fast for an ALP test? +
Your practice decides. Because ALP is usually measured together with other blood values, fasting for several hours is often planned. A fatty meal shortly before the blood draw can raise ALP slightly.
What is hypophosphatasia? +
Hypophosphatasia is a rare inherited condition that affects bones and teeth and goes along with low ALP values. It is one reason why a low value should also be interpreted by a doctor.
Alkaline phosphatase (ALP)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.