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Alkaline Phosphatase
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Alkaline Phosphatase

An alkaline phosphatase (ALP) test measures an enzyme found in your liver and bones to help screen for and diagnose various health conditions.

What is an alkaline phosphatase test?

This test measures the amount of alkaline phosphatase (ALP) in your blood. ALP is an enzyme found in all body tissues, with the highest concentrations in the liver, bile ducts, and bones. Because different parts of the body produce different types of ALP, this test is often used alongside other diagnostics to pinpoint the source of abnormal levels.

Why do I need an alkaline phosphatase test?

Your provider may order this test during a routine checkup or if you exhibit symptoms of liver or bone disease.

Symptoms of liver disease

  • Nausea, vomiting, and lack of appetite
  • Fatigue and weakness
  • Jaundice (yellowing of skin and eyes)
  • Abdominal swelling or pain
  • Swelling in ankles and legs
  • Dark urine or light-colored stool
  • Frequent itching

Symptoms of bone disorders

  • Bone pain
  • Joint inflammation and arthritis
  • Unusually shaped or enlarged bones
  • Broken bones

What happens during the test?

A health care professional will collect a small blood sample from a vein in your arm. The procedure typically takes less than five minutes.

Preparation and Risks

You may be required to fast for several hours before the test. Inform your provider of all medications you take, as some can affect ALP levels. Risks are minimal, typically limited to slight pain or bruising at the needle site.

What do the results mean?

High ALP levels can indicate liver or bone issues. Providers may use an ALP isoenzyme test or liver function tests to determine the cause.

  • High levels (Liver-related): May indicate bile duct blockages, cirrhosis, hepatitis, or mononucleosis.
  • High levels (Bone-related): If liver tests are normal, high ALP may indicate bone disorders like Paget's disease.
  • Moderately high levels: May be associated with Hodgkin lymphoma, heart failure, or certain infections.
  • Low levels: Less common, but may indicate zinc or protein deficiency, malnutrition, pernicious anemia, thyroid disease, Wilson disease, or hypophosphatasia.

Note that pregnancy, childhood growth, and certain medications can naturally influence ALP levels.

Frequently Asked Questions

When ALP is elevated in isolation without corresponding increases in transaminases (AST/ALT), it often points toward a cholestatic process, such as a blockage in the bile ducts, rather than direct liver cell damage. It can also indicate bone-related issues, such as healing fractures, Paget's disease, or hyperparathyroidism. Clinicians typically order an ALP isoenzyme test to determine if the enzyme is coming from the liver or bones to guide further diagnostic imaging or treatment.
Certain medications and supplements can interfere with ALP levels, leading to inaccurate results. Common culprits include anticonvulsants like phenytoin, some antibiotics, and high doses of vitamin D or calcium supplements. It is critical to provide a complete list of all prescription drugs, over-the-counter medications, and dietary supplements to your provider before the test so they can interpret the results in the correct context or adjust the timing of the draw.
LP levels naturally rise during pregnancy, particularly in the second and third trimesters, because the placenta produces its own form of the enzyme. This physiological increase is normal and does not indicate liver disease. However, if ALP levels are extremely high or accompanied by symptoms like itching, dark urine, or abdominal pain, it may signal intrahepatic cholestasis of pregnancy, a condition that requires medical monitoring to ensure the safety of both the mother and the fetus.
While ALP is a stable enzyme, certain lifestyle factors can cause minor fluctuations. High-protein diets or the consumption of fatty meals shortly before the test may slightly elevate levels, which is why fasting is sometimes recommended. Intense physical exertion immediately prior to the blood draw is less likely to affect ALP compared to muscle enzymes like CK, but maintaining a consistent routine and avoiding extreme dietary changes in the 24 hours before the test helps ensure the most accurate baseline measurement.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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