ALPU/L
Liver/bile-duct or bone activity
Also known as: Alkaline Phosphatase
Typical optimal range
30–130 U/L
A typical reference range is around 30–130 U/L, though exact limits vary between laboratories and by age and sex, so your result should always be interpreted against your own lab's reference interval. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of ALP follows NHS and laboratory medicine guidance; NICE guidance on liver disease (including NG49 on non-alcoholic fatty liver disease, now updated to reflect MASLD terminology) and the British Society of Gastroenterology provide relevant clinical context for abnormal liver function tests.
What is ALP?
Alkaline phosphatase (ALP) is an enzyme found mainly in the liver, bile ducts, bone, and intestine. It is released into the bloodstream when these tissues are under stress or unusually active, making it a useful early signal of liver or bile-duct problems and conditions involving high bone turnover. Measuring ALP as part of a liver function panel helps clinicians distinguish between different types of liver or biliary disease and can also point towards bone disorders when other markers are considered alongside it.
What a high ALP means
A raised ALP is a prompt to look closer rather than a diagnosis in itself — it tells you that the liver, bile ducts, or bone may be more active than usual, and further investigation is needed to understand why.
- Bile-duct obstruction. Blockage or inflammation of the bile ducts — from gallstones, primary biliary cholangitis, or certain medications — is one of the most common reasons for a raised ALP. The bile-duct enzyme fraction is particularly sensitive to back-pressure and inflammation within the biliary system.
- Liver disease. Conditions such as MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD), alcoholic liver disease, or drug-induced liver injury can all raise ALP, usually alongside other liver markers such as ALT and GGT, which helps the GP work out the likely cause.
- Bone conditions or high turnover. ALP rises naturally during fracture healing, in Paget's disease of bone, and in conditions with rapid bone remodelling. In teenagers it is commonly elevated because of normal growth-plate activity, and it rises in pregnancy, particularly in the third trimester, due to the placental isoform — both are normal physiological findings.
A raised ALP in isolation (with normal ALT and GGT) often points towards a bone rather than a liver cause. Eating a fatty meal shortly before a blood draw can also transiently raise ALP due to the intestinal isoform, which is why a fasting sample is sometimes preferred.
What a low ALP means
A low ALP result is much less commonly clinically significant than a high one, but persistently low values can occasionally reflect nutritional deficiencies or an underactive thyroid.
- Zinc or magnesium deficiency. ALP requires both zinc and magnesium as co-factors to function, so inadequate intake of either mineral can reduce circulating ALP activity. This is more likely in people with poor dietary variety, malabsorption, or significant weight loss.
- Hypothyroidism or malnutrition. An underactive thyroid slows many metabolic processes, including ALP production, and generalised malnutrition can have a similar effect. Your GP can check thyroid function with a simple blood test if this is suspected.
Mildly low ALP on a single test is rarely acted upon alone; it is usually interpreted alongside the full clinical picture.
Should I be worried?
A single out-of-range ALP result on its own is not a diagnosis, and many common explanations — such as adolescent growth, pregnancy, or a recent meal — are entirely harmless. That said, it is worth mentioning to your GP, particularly if the result is notably elevated, if it is accompanied by symptoms such as jaundice, itching, pale stools, dark urine, or bone pain, or if it persists on repeat testing. Your GP will usually look at ALP alongside other liver markers (ALT, GGT, bilirubin) and may consider bone-specific tests or imaging to work out which tissue the extra ALP is coming from. Repeat testing after a short interval is often the sensible first step before any further investigation.
What actually helps
When a mildly raised or low ALP is thought to be related to lifestyle or nutrition, the following approaches are supported by mainstream evidence.
- Support zinc and magnesium intake. Both minerals are essential co-factors for ALP activity and for broader liver and bone health. Most people can meet their needs through a varied, balanced diet without supplementation.
- Limit alcohol. Alcohol is a direct hepatotoxin and a well-established driver of raised liver enzymes including ALP. Staying within the NHS recommended limit of no more than 14 units per week, spread across the week, gives the liver the best chance to recover.
- Maintain a healthy weight. MASLD — now one of the most common causes of mildly raised liver enzymes in the UK — is strongly linked to excess body weight. Even a modest reduction of 5–10% of body weight has been shown to improve liver enzyme levels in people with this condition.
- Stay physically active. Regular moderate exercise supports liver health, helps maintain a healthy weight, and is associated with better bone density, both of which influence ALP over time. The NHS recommends at least 150 minutes of moderate activity per week.
There is good supporting evidence that certain foods have a positive effect on liver health and help maintain adequate micronutrient status relevant to ALP.
Shellfish and red meat (in moderation)
Among the richest dietary sources of zinc, which is essential for ALP enzyme activity and liver function.
Nuts and seeds
Good sources of both magnesium and zinc, supporting the co-factor requirements of ALP and general metabolic health.
Oily fish
Omega-3 fatty acids found in salmon, mackerel, and sardines have evidence supporting reduced liver fat accumulation, relevant to MASLD-related enzyme rises.
Green leafy vegetables
Provide magnesium alongside folate and antioxidants that support overall liver function; spinach and kale are particularly good sources.
Coffee
Observational evidence consistently associates regular coffee consumption with lower levels of liver enzymes and reduced risk of liver fibrosis, though the mechanism is not yet fully understood.
Wholegrains and legumes
Support a healthy weight and provide sustained fibre, magnesium, and B vitamins that underpin good liver metabolism.
Track your own ALP
Upload a lab PDF and Better Days trends ALP over time, flags it when it drifts, and suggests foods that help.
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Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.