ALP blood test: what it measures and what your result means

Medically reviewed by Dr Lebeth Jacob · 21 October 2026

Quick answer: ALP (alkaline phosphatase) is an enzyme found mainly in your liver and bones. An ALP blood test is part of a liver function test. A high result can come from the liver or bile ducts, or from bone, where it rises with growth, healing or some bone conditions. Other tests, such as GGT, help show which.

What is ALP?

ALP is an enzyme, a protein that speeds up chemical reactions in the body. Most of the ALP in your blood comes from the liver, especially the cells lining the bile ducts, and from bone cells that build new bone. Smaller amounts come from the gut and, in pregnancy, the placenta.

Because it comes from more than one place, a high ALP is read alongside other results rather than on its own.

Why is ALP tested?

  • As part of a routine liver function check
  • You drink alcohol regularly, or take medicines that can affect the liver
  • You have bone pain, or a condition that affects your bones
  • You've noticed yellowing of the skin or eyes, itching, dark urine or pale stools
  • You are being monitored for a liver or bone condition

What does a high ALP result mean?

Some reasons are normal, others need looking into:

  • Growth in children and teenagers, when ALP is naturally higher
  • Pregnancy, especially in the last three months
  • A healing broken bone
  • Liver or bile duct conditions, such as gallstones, fatty liver, or conditions that slow the flow of bile
  • Bone conditions, such as Paget's disease of bone or softened bones from low vitamin D
  • An overactive parathyroid gland
  • Some medicines

If GGT is also raised, the ALP is more likely to be coming from the liver. If GGT is normal, bone is the more likely source.

What does a low ALP result mean?

A low ALP is uncommon and usually not serious. It can be linked to poor nutrition, low zinc or magnesium, or an underactive thyroid. Very rarely it's caused by an inherited bone condition.

What can affect your result?

  • A fatty meal shortly before the test can raise ALP slightly in some people
  • Pregnancy and recent fractures raise it
  • ALP is naturally higher in children and teenagers
  • Follow the fasting instructions for the test you book

When to see a GP

Your results report shows the laboratory's normal range and flags any result outside it. Speak to your GP if:

  • Your ALP is flagged high, especially if other liver tests are also raised
  • You have bone pain, or bones that break easily
  • You have itching, tummy pain or are losing weight without trying

Get medical help the same day (GP or NHS 111) if your skin or the whites of your eyes turn yellow, or you have dark urine and pale stools.

How we test ALP

You can have ALP tested with a blood sample taken at one of our 250+ partner clinics, or with a finger-prick kit at home. Samples are analysed by a UKAS-accredited laboratory. Results are usually ready in 3–5 working days, with a doctor's comments on every result.

Tests that include ALP

Prices for in-clinic tests include your appointment. Compare every test with ALP in the biomarker explorer

Frequently asked questions

What level of alkaline phosphatase is dangerous?

There is no single dangerous number. A slightly raised ALP is often caused by something harmless, such as a healing bone or pregnancy. A high ALP alongside other abnormal liver tests, jaundice or bone pain should be checked by a GP.

What foods should I avoid if my ALP is high?

No food directly lowers ALP. What helps depends on the cause. If it's coming from the liver, cutting down on alcohol and losing extra weight help. If low vitamin D is affecting your bones, vitamin D supplements may be advised.

What causes a high ALP?

Most often a liver or bile duct problem, or bone activity such as growth, healing or a bone condition. Pregnancy raises it too.

How can a doctor tell if high ALP is from the liver or bone?

Usually by looking at GGT. If both are raised, the liver is the likely source. If only ALP is raised, bone is more likely. Sometimes a special test that separates the types of ALP is used.

Is a high ALP normal in teenagers?

Yes. Bones grow fast during childhood and the teenage years, so ALP is naturally much higher than in adults.