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What is ALP?

As part of our biomarker series, we look at alkaline phosphatase (ALP) and what it can tell you about your body.

Perhaps you’ve just taken our Liver Blood Test and want to make sense of your results. Or maybe your alkaline phosphatase (ALP) levels were found to be incidentally high as part of your Advanced Well Man Blood Test or Advanced Well Woman Blood Test.

Either way, we’re going to look at ALP in more detail: its function, the normal ranges, and what it might mean if your levels are raised.  

- What is ALP?
- Why do I need an ALP test?
- What is a normal ALP level?
- What causes a low ALP result?
- What causes a high ALP result?
- What can I do to lower my ALP?
- What should I do if my ALP result is abnormal?

What is ALP?

Alkaline phosphatase (ALP) is an enzyme found throughout the body and circulating in the blood, primarily derived from the liver and bone [1].

ALP has several functions in the body. It plays an important role in metabolism in the liver, breaking down proteins, and the development of the skeleton [2].  

There are four different forms of ALP called isoenzymes, which differ depending on where they originate. This is important to understand why levels of ALP might be raised. For example, placental ALP is produced by the placenta during pregnancy. However, labs do not routinely distinguish between the different types. 

Why do I need an ALP test?

An ALP test is usually included as part of a liver function test or bone profile. You may have this test as part of a routine health screen or because your doctor would like to investigate your liver or bone health. 

An abnormal ALP result can point to a variety of conditions, from damaged liver cells to gallstones, bone disease, or even vitamin D deficiency. Additional examinations, blood tests, or scans may be required to make sense of the results.

The easiest way to check your ALP is with our at-home Liver Blood Test.

What is a normal ALP level?

Serum ALP levels go up and down with age. Levels are highest during childhood and adolescence due to bone growth and development. They peak again in older age.

In non-pregnant adults, a normal ALP level is around 30–130 IU/L. Bear in mind that reference values vary slightly between laboratories.

Other factors affecting ALP levels include: 

  • Pregnancy — Another form of ALP, called placental ALP, is released from the placenta. Therefore, ALP levels are up to twice as high in late pregnancy, mainly during the third trimester [3]. 
  • Ethnicity — ALP is higher among Hispanics and African Americans (by about 10–20%) compared with Caucasians [4].
  • Eating — Eating a fatty meal can cause a slightly elevated ALP level for a few hours in people with blood groups O or B [5]. Ideally, the test should be performed while fasting. 
  • Smoking — People who smoke tend to have a slightly higher ALP level than normal [6]. 

What causes a low ALP result?

Abnormally low ALP levels are uncommon but may be due to malnutrition, medications, or thyroid disease.

Causes of low ALP include [7]

  • Low phosphate levels
  • Zinc or magnesium deficiency
  • Postmenopausal women receiving oestrogen replacement
  • Hypothyroidism (an underactive thyroid)
  • Severe anaemia
  • Wilson’s disease (an inherited disorder that causes copper to accumulate in the organs)
  • The oral contraceptive pill

What causes a high ALP result?

Raised ALP levels can point to many different conditions, usually related to liver or bone disease. If ALP levels are greater than four times the upper limit of normal, this is usually due to a blockage of the bile duct. 

Causes of raised ALP include [8]

  • Blocked bile ducts (caused by gallstones, strictures, infection or, less commonly, cancer)
  • Liver damage (including hepatitis and cirrhosis)
  • Healing bone fractures
  • Paget’s disease of bone
  • Hyperparathyroidism (an overactive parathyroid gland)
  • Diabetes
  • Vitamin D deficiency
  • Untreated coeliac disease

Depending on the cause of your raised ALP levels, you might not have any symptoms. 

If your ALP result is raised due to gallstones, it’s probably because one has got stuck in the bile duct. If this is the case, you’re likely to have severe tummy pain, especially after eating fatty meals, lasting hours at a time. Other signs and symptoms of liver damage include lethargy, jaundice (yellowing of the skin and whites of the eyes), nausea and vomiting, and itchy skin. 

What can I do to lower my ALP?

The best way to improve your ALP levels if they are abnormal is to speak to your doctor who can help you identify and treat the underlying cause. However, there are some general lifestyle changes you can make to protect your liver and overall health. 

Diet has a major impact on liver health. Make sure you’re not eating too much saturated fat — cholesterol plays a role in the formation of gallstones and can lead to fatty liver disease. So too does being overweight, so aim for a healthy body weight [9]. 

Drinking small amounts of alcohol may slightly reduce your risk of gallstones, but in the long term, can affect the function of your liver [9]. Try to keep within the recommended limits of no more than 14 units per week. Find out other ways you can keep your liver healthy. 

Exercising outdoors not only keeps you fit but can boost your vitamin D levels. Vitamin D deficiency — a potential cause of raised ALP levels — is very common in the UK, which is why almost everyone is advised to take a 10µg vitamin D supplement over winter [10]. You can check your levels with our Vitamin D (25 OH) Blood Test

What should I do if my ALP result is abnormal?

As always, if you receive an abnormal blood test result, it’s best to discuss this with your doctor. They will likely ask about your symptoms, perform an examination, and may request further relevant tests. 


References

  1. Lowe D, Sanvictores T, John S. 2021. Alkaline Phosphatase. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
  2. Sharma, U., Pal, D., & Prasad, R. (2014). Alkaline phosphatase: an overview. Indian journal of clinical biochemistry: IJCB, 29(3), 269–278.
  3. Bacq Y. The Liver in Normal Pregnancy. In: Madame Curie Bioscience Database [Internet]. Austin (TX): Landes Bioscience; 2000-2013. 
  4. Gonzalez, H., Imam, Z., Wong, R., Li, J., Lu, M., Trudeau, S., Gordon, S., Imam, M. and Gish, R., 2020. Normal alkaline phosphatase levels are dependent on race/ethnicity: NationalGEP Health and Nutrition Examination Survey data. BMJ Open Gastroenterology, 7(1), p.e000502.
  5. Matsushita M, Harajiri S, Tabata S, Yukimasa N, Muramoto Y, Komoda T. [Alkaline phosphatase activity in blood group B or O secretors is fluctuated by the dinner intake of previous night]. Rinsho Byori. 2013 Apr;61(4):307-12. PMID: 23855186
  6. Wannamethee SG, Shaper AG. Cigarette smoking and serum liver enzymes: the role of alcohol and inflammation. Ann Clin Biochem. 2010 Jul;47(Pt 4):321-6. doi: 10.1258/acb.2010.009303. Epub 2010 May 28. PMID: 20511375.
  7. Sharma, U., Pal, D., & Prasad, R. 2014. Alkaline phosphatase: an overview. Indian journal of clinical biochemistry : IJCB, 29(3), 269–278.
  8. UpToDate. 2022. Causes of an elevated alkaline phosphatase. [online] Available at: <https://www.uptodate.com/contents/image?imageKey=GAST%2F99099&topicKey=GAST%2F3563&source=see_link> [Accessed 21 January 2022].
  9. NHS. 2021. Gallstones. [online] Available at: <https://www.nhs.uk/conditions/gallstones/prevention/> [Accessed 21 January 2022].
  10. NHS. 2022. Vitamin D. [online] Available at: <https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/> [Accessed 21 January 2022].