Alkaline phosphatase, often shortened to ALP or alk phos, is part of the routine liver panel and comprehensive metabolic panel, so it shows up on many blood tests whether you asked for it or not. A high result is common, and a low one is rarer and easy to overlook. This guide explains what alkaline phosphatase is, the normal range, what high and low levels can mean, what level is a concern, which follow-up tests come next, and where research on related liver and bone conditions stands.
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What alkaline phosphatase is
Alkaline phosphatase is an enzyme found mainly in the liver and the bones, with smaller amounts in the bile ducts, kidneys, and intestines, and in the placenta during pregnancy. In the liver it is concentrated in the cells that line the bile ducts, so it rises when bile does not flow freely. In bone it comes from the cells that build new bone, so it rises when bone is growing or being repaired.
That two-source pattern is the key to reading the result. Unlike ALT, which comes mostly from liver cells, a high ALP does not tell you on its own whether the liver or the bones are involved.
Alkaline phosphatase normal range
Labs use different methods, so normal ranges vary. Common adult ranges include 40 to 129 IU/L, 44 to 147 IU/L, and 30 to 120 IU/L. Always compare your result with the range printed on your own report.
Why ALP is higher in children, teens, and pregnancy
Levels are normally higher in children and teenagers because their bones are growing, and they are normally higher during pregnancy because the placenta makes ALP. Between about 15 and 50, levels tend to be slightly higher in men than in women, and they rise again with age. A result that would be high for an adult can be normal for a growing child or a pregnant woman.
What high alkaline phosphatase can mean
Doctors usually sort the causes of high ALP into two groups.
Liver and bile duct causes
- A blocked or narrowed bile duct, for example from gallstones, a stricture, or less often a tumor.
- Hepatitis and cirrhosis.
- Autoimmune bile duct diseases, mainly primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), described below.
- Cholestasis of pregnancy, a condition in which bile flow slows in late pregnancy.
- Some medicines, and infections such as mononucleosis.
Bone causes
- A healing fracture, or normal growth in children and teens.
- Paget disease of bone, in which bone is broken down and rebuilt too quickly.
- Osteomalacia, softening of the bones often caused by low vitamin D.
- An overactive parathyroid or thyroid gland.
- Cancer that has spread to the bones, for example from prostate or breast cancer, and less often a bone tumor.
Other causes include untreated celiac disease, some lymphomas and leukemias, sarcoidosis, and, for people with blood type O or B, eating a fatty meal shortly before the test.
What level of alkaline phosphatase is dangerous?
There is no single number that is dangerous for everyone, and doctors judge it against your lab’s upper limit and your other results. As a rule of thumb, a mild rise often has a harmless cause and may simply be repeated and watched. A very high level, several times the upper limit, more often points to a bile duct problem or a bone disorder and should be looked into promptly.
What matters more than the number is what comes with it. Get medical advice soon if a high ALP comes with yellowing of the skin or eyes, dark urine, pale stools, itching, pain in the upper right side of the abdomen, unexplained weight loss, or bone pain and fractures.
How doctors find out whether it is liver or bone
The usual next step is a GGT test, another liver enzyme. American College of Gastroenterology guidelines advise confirming that a high ALP comes from the liver with GGT: if GGT is also high, the liver or bile ducts are the likely source; if GGT is normal, bone becomes more likely. An ALP isoenzyme test can also show which organ the enzyme came from, though not every lab offers it.
If the liver is the source, doctors look at the pattern with ALT, AST, and bilirubin, and usually order an ultrasound of the liver and bile ducts. Guidelines also recommend an antimitochondrial antibody (AMA) blood test to check for primary biliary cholangitis. If bone is the source, vitamin D, calcium, and parathyroid hormone are common next tests, sometimes with a bone scan.
What low alkaline phosphatase can mean
A low ALP is less common and often goes unnoticed, because many lab reports focus on high values. Possible causes include malnutrition or low protein intake, zinc or magnesium deficiency, an underactive thyroid, pernicious anemia, and Wilson disease, a rare inherited condition in which copper builds up in the body.
Hypophosphatasia: the rare cause worth knowing
Hypophosphatasia (HPP) is a rare inherited disease in which the body makes too little working alkaline phosphatase, so bones do not mineralize properly. A persistently low ALP is its hallmark. Severe forms appear in infancy and affect about 1 in 100,000 newborns, while milder adult forms may be more common and are often found only after years of fractures that heal slowly, bone or muscle pain, or early loss of teeth.
In October 2015 the FDA approved Strensiq (asfotase alfa), the first treatment for perinatal, infantile, and juvenile-onset HPP. A newer enzyme therapy is in phase 3 trials that have finished enrolling. If you have a low ALP on more than one test along with fractures or bone pain, it is reasonable to ask your doctor whether HPP has been considered.
How to lower alkaline phosphatase
ALP comes down when the cause is treated. There is no diet or supplement that lowers it directly. In practice that can mean treating a blocked bile duct or gallstones, stopping a medicine that is causing it, correcting low vitamin D, or treating a thyroid or parathyroid problem. A rise from a healing fracture or from pregnancy settles on its own. Do not stop any prescribed medicine without talking to your doctor.
When a high ALP points to bile duct disease, and why research matters
For some people, a persistently high ALP is the first sign of primary biliary cholangitis, an autoimmune disease that slowly damages the small bile ducts in the liver and mostly affects women. ALP is so central to PBC that it is used to judge whether treatment is working. In 2024 the FDA gave accelerated approval to two new PBC medicines used with or instead of the standard drug ursodiol: Iqirvo (elafibranor) in June and Livdelzi (seladelpar) in August. In the seladelpar trial, ALP returned to normal in 25% of people after 12 months, compared with none on placebo.
Studies are recruiting across the US for primary biliary cholangitis, primary sclerosing cholangitis, and MASH, the inflamed form of fatty liver disease, and you can browse liver studies near you on AllClinicalTrials.com. Most add a new medicine to the treatment you already take, and some compare it with a placebo. Nothing is decided until you have gone through informed consent, and participation is voluntary at every step.
Three things to have ready: your latest liver panel, including ALP, GGT, ALT, AST, and bilirubin, with dates; any ultrasound, FibroScan, or AMA result; and the name of your diagnosis, if you have one.
If you have been told you have fatty liver, our guide to fatty liver treatment options explains what the studies are testing.
Common questions
What is a normal alkaline phosphatase level? For adults, many labs use a range of roughly 40 to 130 IU/L, though some go up to about 147. Children, teenagers, and pregnant women normally have higher levels. Check the range on your own report.
Should I worry about slightly high alkaline phosphatase? Usually not on its own. A mild rise often has a harmless cause, such as a healing fracture, a recent fatty meal, or a medicine. Your doctor will usually repeat the test and check GGT to see whether it comes from the liver or bone.
What foods should I avoid if my alkaline phosphatase is high? No food has been shown to lower ALP directly, because the level reflects what is going on in your liver or bones. If you have blood type O or B, avoiding a fatty meal before the test can prevent a falsely high reading. If the cause is fatty liver, cutting back on alcohol and sugar helps the liver itself.
Can low vitamin D cause high alkaline phosphatase? Yes. Long-term low vitamin D can cause osteomalacia, softening of the bones, which raises bone ALP. It is checked with a simple blood test.
Is low alkaline phosphatase serious? Often it reflects nutrition, such as low zinc or protein, or an underactive thyroid. A persistently low level with fractures, bone pain, or early tooth loss can point to hypophosphatasia, which is worth asking about.
Do liver study participants get paid? Some studies offer compensation for time and travel, and study related care is typically provided at no cost to participants. Compensation varies by trial and is always described during the informed consent process before you agree to anything.