ALP Levels Explained: What a High Alkaline Phosphatase Means

ALP, short for alkaline phosphatase, is an enzyme found mainly in the liver, the bile ducts and the bones. An ALP blood test measures how much of it is in your blood. Because it comes from more than one place, a high ALP can point to the liver or to bone, and working out which is the key step.

This guide goes deeper on ALP alone: typical ranges, how GGT helps find the source, common causes, when to retest and the symptoms that need prompt help. For the full set of liver markers, see our liver function test results guide.

Test it in Chiswick: our ALP blood test costs £59, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Prefer to test at home? See our home kit options.

Better value: our Liver Function Check costs £49 and measures ALP together with GGT, ALT, AST, bilirubin and albumin, so you can see straight away whether the liver is the likely source. Book the Liver Function Check.

Quick answer

ALP is an enzyme from the liver, bile ducts and bone. As an example, one NHS laboratory uses an adult range of 30 to 130 U/L, but ranges vary by laboratory and age, so check the range on your report. If ALP and GGT are both raised, the liver or bile ducts are the more likely source. If ALP is raised with a normal GGT, bone is more likely, and vitamin D is often checked. Higher levels are normal in growing children and in later pregnancy. A result outside the range is a prompt to find the reason, not a diagnosis.

What is ALP?

ALP is made by cells lining the small bile ducts in the liver and by bone-building cells. Smaller amounts come from the gut and, in pregnancy, the placenta. When bile flow is slowed or bone turnover increases, more ALP enters the blood. It is reported in U/L or IU/L and is usually read with GGT, ALT and bilirubin, because the pattern shows where the rise is coming from.

Normal ALP levels

Each laboratory sets its own range, so always use the one on your report. As an example, one NHS laboratory uses 30 to 130 U/L for adults. Keep in mind:

• Children and teenagers: ALP is naturally much higher during growth spurts, often well above the adult range.
• Pregnancy: ALP rises in the second half of pregnancy because the placenta makes it.
• Older adults: ALP can drift up slightly with age, particularly in women after the menopause.

Liver or bone? How GGT helps

UK guidance on abnormal liver blood tests suggests using GGT to help locate the source of a raised ALP:

• ALP and GGT both raised: the liver or bile ducts are the likely source. This is sometimes called a cholestatic pattern.
• ALP raised, GGT normal: bone is the likely source. Calcium, phosphate and vitamin D are often checked next.

Laboratories can also separate ALP into liver and bone forms (isoenzymes) when the source is unclear, usually arranged by your GP or a specialist.

Common causes of a high ALP

Liver and bile duct causes

• Gallstones blocking or narrowing a bile duct, often with pain in the upper right tummy
• Fatty liver and alcohol, usually with ALT or GGT also raised
• Medicines, including some antibiotics and other drugs that slow bile flow
• Less common conditions such as primary biliary cholangitis and primary sclerosing cholangitis, where liver antibodies or a scan help

Bone causes

• Low vitamin D, which can lead to softening of the bones (osteomalacia). Our vitamin D levels guide explains this further.
• Healing fractures, which increase bone building for several weeks
• Paget's disease of bone, more common over 50
• An overactive parathyroid gland, often with a high calcium. See our calcium levels guide.

Low ALP

A low ALP is less common. It can be linked with low zinc or magnesium, malnutrition, an underactive thyroid or, rarely, an inherited condition. It is usually discussed if it stays low.

What usually happens after a high ALP

1. Check GGT and the rest of the liver profile. This points towards liver or bone.
2. Review medicines and recent events. A recent fracture or new medicine can explain a rise.
3. Liver route: your GP may suggest an abdominal ultrasound and liver antibodies.
4. Bone route: calcium, phosphate, vitamin D and sometimes parathyroid hormone are checked.
5. Repeat the test to see whether the rise persists, as a single mild rise often settles.

When to get urgent help

• Ask for an urgent GP appointment or contact NHS 111 if your skin or the whites of your eyes look yellow, or you have dark pee, pale poo or itchy skin.
• Get same-day medical advice if you have pain in the upper right tummy with a high temperature or shivering.
• Call 999 or go to A&E if you have severe tummy pain that does not ease, or you are vomiting blood.

Speak to your GP soon about new bone pain, unexplained weight loss or a high ALP that does not settle.

Who should consider an ALP test?

• Anyone following up a previous raised ALP
• People with risk factors for fatty liver, or who drink regularly
• People with possible low vitamin D, such as those who get little sun
• People taking medicines that can affect the liver

Preparing for your test

Fasting is not usually needed for ALP, but ALP can rise slightly after a fatty meal in some people, so a light meal beforehand is sensible. We will tell you if another test in your booking needs fasting. Tell us about recent fractures, pregnancy, medicines and supplements.

How often to retest

A mild, isolated rise is often repeated after 1 to 3 months. If a cause has been found, retesting follows your GP's plan. Persistent rises usually lead to further tests rather than repeated checks of ALP alone.

Frequently asked questions

Is an ALP of 150 high?

It is above many adult ranges but is a mild rise. Checking GGT, vitamin D and the other liver markers helps show the likely source.

Can low vitamin D cause high ALP?

Yes. Long-term low vitamin D can affect bone and raise ALP. A vitamin D blood test (£59) is a common next step.

Why is my teenager's ALP so high?

During growth spurts ALP is naturally much higher than adult ranges. Laboratories use age-specific ranges for children.

Does a high ALP mean cancer?

Rarely. Most raised results have common causes such as gallstones, fatty liver, low vitamin D or a healing fracture. Persistent unexplained rises are always looked into.

ALP testing in Chiswick

We take your blood sample at our clinic at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station on the District line (Piccadilly line trains stop there early morning and late evening only), and on the 94, E3 and 272 bus routes. Limited parking is available on request when you book. Your sample is analysed by the Randox laboratory, and a practitioner talks you through what your result means. No GP referral is needed, and we can send a GP feedback report on request.

Book a single ALP blood test, or check ALP with GGT and four more markers in our Liver Function Check. You can also compare every blood test and price, read our GGT levels guide or our liver function test results guide.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.