Alkaline Phosphatase (ALP) Test: Normal Range, High and Low Causes
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: November 2026 · How we review
Quick Answer: What is an alkaline phosphatase (ALP) test?
An alkaline phosphatase (ALP) test is a simple blood test that measures how much of the ALP enzyme is in your blood. Most ALP comes from the liver and bones, so the test helps screen for, diagnose and monitor liver, bile duct and bone conditions. It cannot diagnose a condition on its own [1].
What the research says
An unexplained, isolated high ALP often points to a serious underlying cause. In 260 adults with a raised ALP and no obvious explanation, 57% had an underlying cancer (mostly spread to the liver or bone), 29% had bone disease and 7% had liver disease that had not been suspected; 47% died within an average of 58 months. (Jones and Rockey, The American Journal of the Medical Sciences, 2025) [2]
Higher ALP in the general population is linked to higher overall death risk. A meta-analysis of 19 cohort studies covering more than 9.24 million people found that those in the top third of ALP levels had a 38% higher risk of death from any cause than those in the bottom third (relative risk 1.38). (Kunutsor et al., International Journal of Epidemiology, 2014) [3]
Raised ALP has also been tied to ischemic stroke risk. A 2025 systematic review and meta-analysis found that higher ALP levels were associated with a 60% higher risk of ischemic stroke (risk ratio 1.60), though the certainty of the evidence was rated low or very low. (El-Sayed et al., BMC Neurology, 2025) [4]
Key takeaways
ALP is an enzyme found mainly in the liver and bones, with smaller amounts in the bile ducts, kidneys, intestines and, during pregnancy, the placenta [1].
The test is a routine blood draw, often included in a comprehensive metabolic panel (CMP) or liver panel, and takes less than five minutes [1].
A commonly used normal range is 44 to 147 IU/L, though some labs use 30 to 120 IU/L, so always check the range printed on your own report [1].
High ALP usually points to a liver, bile duct or bone problem, but mild rises often have harmless causes [1].
Low ALP is less common and may be linked to nutrition problems, an underactive thyroid or rare genetic conditions [1].
Children, teenagers, older adults and pregnant people often have higher levels that are normal for them [1].
What is alkaline phosphatase?
Alkaline phosphatase is an enzyme that is present throughout your body. Scientists still do not know its exact job, but it is believed to play a part in several body processes [1].
It is often called a liver enzyme because the liver holds the largest share. It is also found in bone, the bile ducts, the kidneys and the intestines, and the placenta makes it during pregnancy [1].
Most of the ALP in your bloodstream comes from two places: the liver and the bones. That is why an abnormal result usually leads your provider to look at one of these two systems [1].
What is an ALP test used for?
Providers order an ALP test to screen for, help diagnose or monitor conditions that affect the liver, the bile ducts or the bones. It can also be part of the workup when you have vague symptoms, such as ongoing tiredness [1].
Which symptoms might lead to an ALP test?
Your provider may suggest the test if you have signs of a liver problem [1]:
Yellowing of the skin or the whites of the eyes (jaundice)
Pain or swelling in the belly, especially on the right side
Bruising easily
Nausea or vomiting
Dark urine or pale stools
Weight loss you cannot explain
Fatigue
Swelling in the legs or other areas (edema)
The test may also be ordered for signs of a bone disorder, such as bone or joint pain, bones that are enlarged or abnormally shaped, or breaking bones more often than expected [1].
What types of ALP tests are there?
There are two main kinds of ALP blood test. The general ALP test is the one most people get, while the isoenzyme test is usually saved for follow-up [1].
Test | What it measures | When it is used |
General ALP test | Total amount of ALP in your blood | Routine screening, often as part of a CMP or liver panel |
ALP isoenzyme test | Which tissue the ALP came from, such as liver or bone | Usually after an abnormal general ALP result |
Sources: [1]
The isoenzyme test is more technically complex and costly, and not every lab offers it [1]. A liver panel or CMP adds other measurements, including other liver enzymes, which gives your provider a fuller picture than ALP alone [1].
How do you prepare for an ALP blood test?
If your ALP is being checked as part of a comprehensive metabolic panel, you will usually need to fast for 10 to 12 hours beforehand. You can still drink water [1].
Your provider may give you different instructions depending on the other tests being run, so follow the advice you are given [1]. Tell your provider about any medicines you take, since some, such as birth control pills, can affect ALP levels [1].
What happens during an ALP test?
A trained phlebotomist usually collects the sample, and a medical laboratory scientist then runs it on specialized analyzers [1].
The draw follows a few quick steps, shown below.
The whole blood draw usually takes less than five minutes from start to finish.
Does an ALP blood test hurt?
Most people feel only a quick pinch or sting as the needle goes in. The discomfort passes quickly [1].
What are the risks of an ALP test?
Blood tests carry very little risk. You may notice mild soreness or a small bruise where the needle went in, and this usually clears up fast [1].
What is a normal ALP level?
Your lab report usually lists the test name, your result, the lab's normal range and a flag showing whether your value is normal, high or low [1].
Reference ranges differ from lab to lab. A widely used range is 44 to 147 international units per liter (IU/L), while some organizations list 30 to 120 IU/L [1]. Your own lab's range is the one that matters for your result.
Normal ALP levels also change with age, sex and life stage.
Because levels shift across life, your provider reads your number against your age and situation.
Group | How ALP tends to compare |
Children and teens in puberty | Higher, because bones are growing |
Adults aged 15 to 50 | Slightly higher in males than in females |
Older adults | Rises again with age |
Pregnancy | May be higher |
Healing bone fracture | May be higher |
Sources: [1]
About 1 in 20 healthy people have a result that falls outside the normal range, so an out-of-range value is not automatically a sign of disease [1].
What causes high alkaline phosphatase?
A very high ALP often signals liver damage or a bone disorder. A small rise, on the other hand, frequently has a harmless cause and may simply be watched and rechecked over time [1].
The main groups of causes are summarized below.
Your provider will decide which group fits best using your symptoms and other test results.
Liver and bile duct causes
Liver and bile duct conditions that can raise ALP include [1]:
Cholestasis of pregnancy
Cirrhosis
Hepatitis
Biliary atresia in infants
Biliary stricture, a narrowing of a bile duct
A bile duct blocked by cancer, such as cholangiocarcinoma or cancer in the head of the pancreas
Mononucleosis
Bone causes
Bone conditions that can raise ALP include [1]:
Cancer that has spread to the bone (bone metastasis)
Paget's disease of bone
Osteogenic sarcoma, a type of bone cancer
Fractures that are healing
Hyperparathyroidism
Hyperthyroidism
Osteomalacia, most often caused by vitamin D deficiency
Other causes
A high ALP level may also be a sign of celiac disease that has not been treated [1]. When the cause is unclear, research shows that an isolated high ALP deserves careful follow-up, as many such cases trace back to cancer in the liver or bone or to bone disease [2].
What causes low alkaline phosphatase?
Low ALP is less common than high ALP. Possible causes include [1]:
Malnutrition
Low zinc or low magnesium
Hypothyroidism (an underactive thyroid)
Rare inherited conditions, such as hypophosphatasia and Wilson disease
What else can affect your ALP result?
Several factors besides disease can move your ALP level up or down [1]:
Certain medicines, including birth control pills
What you eat
Pregnancy
Age, since children and teens tend to have higher levels
AIDS
Mistakes in how the sample was collected or handled
What happens after an abnormal ALP result?
Your provider looks at your full picture before deciding on next steps. This includes your medical history, current medicines, how far your result is from normal, your other lab results and your symptoms [1].
Depending on these factors, you may need repeat testing, an ALP isoenzyme test to find where the extra ALP is coming from, or other tests aimed at the liver or bones [1]. Results generally come back within one to two business days, though some take longer [1].
When should you call your doctor?
Contact your provider if you notice symptoms of liver damage, such as yellowing skin or eyes, or symptoms of a bone disorder, such as bone or joint pain [1].
If you have already been diagnosed with a condition linked to ALP, reach out whenever you develop new or worrying symptoms [1].
Conclusion
The ALP test is a quick, low-risk blood test that gives your provider a window into your liver, bile ducts and bones. Because ALP comes from several tissues and normal levels change with age, sex and pregnancy, a single number is a clue rather than a diagnosis [1].
If your result is high or low, your provider will weigh it alongside your symptoms and other tests, and may order an isoenzyme test or further workup. Mild changes often turn out to be harmless, while large or unexplained rises call for a closer look [1, 2].
Keep learning: Read about Hepatitis: Causes, Symptoms, and Modern Treatment Options, What Is Bile Duct Obstruction? Symptoms, Causes, Diagnosis, and Treatment Explained and Celiac Disease: How Gluten Damages Your Gut, and How a Gluten-Free Diet Can Heal It.
FAQ
What is an alkaline phosphatase test?
It is a blood test that measures the level of ALP, an enzyme that comes mostly from your liver and bones. It helps providers check for liver, bile duct and bone problems.
Why would my doctor order an ALP test?
It may be ordered as part of a routine metabolic or liver panel, or because you have symptoms such as jaundice, belly pain, bone pain or unexplained fatigue. It is also used to monitor known liver and bone conditions.
Do I need to fast before an ALP test?
If the test is part of a comprehensive metabolic panel, you usually need to fast for 10 to 12 hours, though water is allowed. Follow the instructions your provider gives you.
Does the ALP blood test hurt?
You may feel a brief pinch when the needle goes in. Any soreness or bruising afterward is usually mild and short-lived.
How long does an ALP test take?
The blood draw takes less than five minutes. Results usually arrive within one to two business days.
What is a normal ALP level?
A commonly used range is 44 to 147 IU/L, and some labs use 30 to 120 IU/L. Normal values vary by lab, age and sex, so compare your result with the range on your report.
What does a high ALP level mean?
A high level often points to a liver, bile duct or bone condition, such as hepatitis, a blocked bile duct, Paget's disease of bone or a healing fracture. Mild rises often have harmless causes and may just be rechecked.
What does a low ALP level mean?
Low ALP is uncommon. It may be linked to malnutrition, low zinc or magnesium, an underactive thyroid or rare genetic conditions such as hypophosphatasia.
Can an ALP test diagnose a disease on its own?
No. An ALP result shows that something may be affecting the liver or bones, but your provider needs other tests, such as an isoenzyme test or liver panel, to find the cause.
Are there risks to an ALP blood test?
The risks are very low. The most common side effect is mild tenderness or a small bruise where the blood was drawn.
When should I call my doctor about ALP?
Call your provider if you have signs of liver damage, such as yellow skin or eyes, or signs of a bone problem, such as bone or joint pain. Also call if you develop new or worrying symptoms after a diagnosis.
Related Reading
Paget's Disease of Bone: Symptoms, Causes, and Treatment — A Guide for Adults Over 50 explains the bone remodeling disorder that is one of the classic causes of a high ALP level.
Osteomalacia: Symptoms, Causes, and Management Strategies covers the bone-softening condition, most often due to low vitamin D, that can raise ALP.
Cirrhosis of the Liver: What It Is, How Permanent Scarring Damages Your Liver, and What Treatment Involves explains the permanent liver scarring that is one of the liver conditions behind a high ALP result.
What Is Cholestasis? Causes, Symptoms, Diagnosis and Treatment covers reduced bile flow, a common reason for a raised ALP.
Understanding Hypophosphatasia: Causes, Symptoms, and Life-Long Management explains the rare inherited condition marked by low ALP levels.
References
Cleveland Clinic. Alkaline Phosphatase (ALP): What It Is, Causes & Treatment. Cleveland Clinic. Last updated November 4, 2021. https://my.clevelandclinic.org/health/diagnostics/22029-alkaline-phosphatase-alp
Jones W, Rockey DC. An observational study of the causes of an isolated elevated alkaline phosphatase level of unclear etiology. Am J Med Sci. 2025;369(3):354-358. PMID 39454727. https://doi.org/10.1016/j.amjms.2024.10.003
Kunutsor SK, Apekey TA, Seddoh D, et al. Liver enzymes and risk of all-cause mortality in general populations: a systematic review and meta-analysis. Int J Epidemiol. 2014;43(1):187-201. PMID 24585856. https://doi.org/10.1093/ije/dyt192
El-Sayed OS, Alnajjar AZ, Arafa A, et al. Association between risk of ischemic stroke and liver enzymes levels: a systematic review and meta-analysis. BMC Neurol. 2025;25(1):18. PMID 39806288. https://doi.org/10.1186/s12883-024-03875-x
Medical disclaimer
This article is for general education only and does not replace advice from a qualified healthcare professional. Talk to your doctor about your own diagnosis and treatment, and seek emergency care right away for severe or sudden symptoms.
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