What is ALP?
Alkaline phosphatase is an enzyme that clips phosphate groups off molecules, and that happens in two places that have nothing to do with each other. In the wall of the bile ducts, where it helps with the drainage of bile, and in the osteoblasts, the cells that make new bone and fix minerals into it. What circulates in your blood is the sum of those two, and the number itself does not say which source it comes from. That is why you never read ALP alone. Gamma-GT does come from the bile ducts and not from bone, so high ALP with high gamma-GT is the bile drainage, and high ALP with normal gamma-GT is bone. Bilirubin confirms the bile side if it rises with it, and calcium, phosphate and vitamin D tell what is going on at the bone side. During growth, in the last months of a pregnancy and in the weeks after a fracture a high ALP is normal, because plenty of bone is being made. Your report shows ALP in U/L. Normal is about 45 to 115 U/L for a man of 19 to 50 years and 38 to 98 U/L for a woman, and in later age the band shifts slightly upward, because bone turnover increases. After a fatty meal ALP rises temporarily, especially in blood groups O and B, so have blood drawn fasting if you want to compare.
Why is ALP relevant?
The reason ALP is interesting for anyone who wants to stay healthy sits on the bone side. With a vitamin D deficiency your gut absorbs too little calcium, and your bone cells work harder to mineralise the bone anyway; ALP then rises while the rest of your liver values are normal. A slightly raised ALP with a normal gamma-GT and a low vitamin D is thereby one of the ways a vitamin D deficiency gives itself away before it shows in your bone density. Daylight, oily fish and a supplement in winter bring it back. After the menopause ALP rises too, because bone turnover speeds up; that is the phase in which bone is lost, and strength training, protein, calcium and vitamin D are the levers. The liver side is a different story. Gallstones, a narrowing or inflammation of the bile ducts, and some medicines let ALP rise together with gamma-GT, often with bilirubin alongside and pain in the upper right of the abdomen after a fatty meal. That is a picture you recognise by the combination and that is looked into with imaging of the bile ducts. Fatty liver and alcohol, the usual reasons for a high ALT and gamma-GT, usually lift ALP only a little. A low ALP is usually nothing. It occurs with a deficiency of zinc or magnesium, which the enzyme cannot do without, with an underactive thyroid, with malnutrition, and rarely with an inherited condition in which the enzyme is missing. In anyone who eats one-sidedly or drinks a lot, zinc is the first question.
ALP reference ranges
What counts beside the number:
- Gamma-GT, the referee: if it rises with it, it is the bile ducts; if it stays normal, it is bone
- Bilirubin and ALT on the bile side, which go up with a congested drainage
- Vitamin D, calcium and phosphate on the bone side
- Whether you are pregnant, in the menopause or recently had a fracture
- Whether you were fasting, because a fatty meal lifts ALP temporarily
- With a low value: zinc, magnesium and TSH
The bands above are where the labs overlap from 19 to 50 years; some labs let the band rise with age, others use one upper limit. During growth, in the last months of a pregnancy and after a fracture a high value is normal. More important than the band is gamma-GT beside it: that says whether a high ALP comes from the bile ducts or from bone.
What Dutch labs actually use
38 – 98U/L
Between 0 and 38 and between 98 and 123 it depends on the lab, because each sets its limits on its own method and population. Above 123 every lab calls it abnormal.
every lab calls 38 – 98 U/L normal. Between 0 and 38 and between 98 and 123 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Women 15–18 yrs | 54–143 U/L |
| Men 15–18 yrs | 59–294 U/L | |
| Women 19–50 yrs | 38–123 U/L | |
| Women 51–65 yrs | 48–142 U/L | |
| Women 66–80 yrs | 47–138 U/L | |
| Women 81+ | 45–146 U/L | |
| Men 19–50 yrs | 45–128 U/L | |
| Men 51–65 yrs | 46–126 U/L | |
| Men 66–80 yrs | 44–134 U/L | |
| Men 81+ | 45–145 U/L | |
| Star-shl2026 | Men 13–18 yrs | 63–190 U/L |
| Women 13–18 yrs | 44–149 U/L | |
| Men 19–50 yrs | 45–128 U/L | |
| Women 19–50 yrs | 38–123 U/L | |
| Men 51–65 yrs | 46–126 U/L | |
| Women 51–65 yrs | 48–142 U/L | |
| Men 66–80 yrs | 44–134 U/L | |
| Women 66–80 yrs | 47–138 U/L | |
| Men 81+ | 45–145 U/L | |
| Women 81+ | 45–146 U/L | |
| Certe2026 | Men 17–18 yrs | 60–158 U/L |
| Women 17–18 yrs | 50–93 U/L | |
| Men 19+ | < 115 U/L | |
| Women 19+ | < 98 U/L | |
| Clinical Diagnostics2026 | Men | < 115 U/L |
| Women | < 98 U/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
ALP high or low: what it means
A high ALP means a bile drainage that falters or bones that are busy. Usually it is the first and rarely the last: bone turnover through growth, healing of a fracture or the menopause; bile congestion; a pregnancy; medicines; a vitamin D deficiency; and rarely a bone disease such as Paget's disease or metastases in bone. Gamma-GT is the referee: if it rises with it, it is the bile ducts, if it stays normal, it is bone. On the bone side vitamin D, calcium and phosphate say what is going on. A low ALP usually means nothing. With a deficiency of zinc or magnesium, an underactive thyroid or malnutrition the value sits lower, and in anyone who eats one-sidedly zinc is the first question. What you do about it: with a high ALP and a low vitamin D, vitamin D is the lever, with daylight, oily fish and a supplement in winter, and after a few months ALP should fall with it. With a high ALP with a high gamma-GT and symptoms, imaging of the bile ducts belongs; waiting with a fatty meal until after the draw prevents a falsely high value. After the menopause, strength training, protein, calcium and vitamin D are the levers for bone turnover. ALP belongs beside gamma-GT, and beyond that beside bilirubin on the bile side and vitamin D, calcium and phosphate on the bone side. Have blood drawn fasting, and compare over time at the same lab.
What lowers it
Usually nothing, and otherwise an enzyme missing its helpers.
| Cause | How often |
|---|---|
| Naturally lowAnyone with no bone being built and a quiet bile drainage sits low in the band, and that is not a finding | Often |
| Malnutrition or zinc deficiencyThe enzyme needs zinc and magnesium to work; with one-sided eating, plenty of alcohol or poor absorption the value falls, and an underactive thyroid does the same | Rare |
What raises it
Bones that are busy, or a bile drainage that falters.
| Cause | How often |
|---|---|
| Bone turnoverGrowth, healing of a fracture and the accelerated turnover after the menopause; ALP rises with a normal gamma-GT, and that is bone | Often |
| Blocked bile flowGallstones, a narrowing or an inflammation of the bile ducts; gamma-GT and bilirubin rise with it, often with pain in the upper right after a fatty meal | Often |
| PregnancyThe placenta makes an ALP of its own and the baby's bones are being built; in the last months a high value is normal | Often |
| MedicationSome drugs against epilepsy, antibiotics and the pill burden the bile ducts; the rise is then explained | Sometimes |
| Vitamin D deficiencyWithout enough vitamin D the gut absorbs too little calcium and the bone cells work harder; ALP rises with a normal gamma-GT, and daylight and a supplement bring it back | Sometimes |
| Bone diseasePaget's disease, a parathyroid gland making too much, or metastases in bone; rare, and then ALP is sharply high with a normal gamma-GT | Rare |
How does an ALP blood test work?
- Referral
- Not needed. ALP is in every liver panel you can have measured yourself, together with gamma-GT and bilirubin.
- Fasting
- Yes, if you want to compare, because after a fatty meal ALP rises temporarily, especially in blood groups O and B.
- When
- Not in the weeks after a fracture or an operation on bone, and not in the last months of a pregnancy if you want to know your usual value.
- The draw
- One tube of blood from a vein in your arm. Gamma-GT, bilirubin, vitamin D and calcium come from the same draw.
- Repeating
- Three months after topping up vitamin D to see whether ALP falls with it; with a bile picture together with imaging of the bile ducts.
- Which test
- ALP is in the Biological age test (€69) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is ALP?
Alkaline phosphatase, an enzyme from the wall of your bile ducts and from the cells that make new bone. What circulates in your blood is the sum of those two, and the number itself does not say where it comes from. Gamma-GT tells the difference, because it rises with the bile ducts and not with bone. In growing children a high ALP is normal.
What is a normal ALP level?
About 45 to 115 U/L for a man of 19 to 50 years and 38 to 98 U/L for a woman, where the labs overlap; in later age the band shifts slightly upward because bone turnover increases. More important than the band is gamma-GT beside it, and whether you were fasting, because a fatty meal lifts ALP temporarily.
What does a high ALP mean?
That your bile drainage falters or your bones are busy. Gamma-GT tells which: if it rises with it, it is the bile ducts, with gallstones as the most common reason; if it stays normal, it is bone, through growth, healing of a fracture, pregnancy, the menopause or a vitamin D deficiency. Rare is a bone disease, and then ALP is sharply high. A slightly raised ALP with a normal gamma-GT and without symptoms is almost always bone and usually harmless.
What does a low ALP mean?
Usually nothing. The enzyme needs zinc and magnesium to work, so with a deficiency of those, with malnutrition and with an underactive thyroid the value sits lower. In anyone who eats one-sidedly or drinks a lot, zinc is the first question. Rare is an inherited condition in which the enzyme is missing, and that stands out through bone problems from a young age.
What does vitamin D have to do with ALP?
Without enough vitamin D your gut absorbs too little calcium, and your bone cells work harder to mineralise the bone anyway. ALP then rises while gamma-GT and the other liver values are normal. So a vitamin D deficiency gives itself away in ALP before it shows in your bone density. Daylight, oily fish and a supplement in winter bring it back within a few months.
Why does ALP rise after the menopause?
Because bone turnover speeds up as soon as oestrogen falls away: more bone is broken down and, to keep up, more is made too, and the cells that make bone leak ALP. That is the phase in which bone is lost. Strength training, enough protein, calcium and vitamin D are the levers you have yourself, and a bone density scan says how things stand.
How do I recognise a problem in the bile ducts?
By the combination: ALP high, gamma-GT high, often bilirubin high, and complaints in the upper right of the abdomen, especially after a fatty meal. Gallstones are the most common reason, and beyond that a narrowing or inflammation of the bile ducts and some medicines. That picture is looked into with an ultrasound of the bile ducts. Fatty liver and alcohol lift ALP only a little.
Do I need to fast for an ALP test?
Yes, if you want to compare: after a fatty meal ALP rises temporarily, especially in blood groups O and B. Also do not have blood drawn in the weeks after a fracture if you want to know your usual value. Gamma-GT, bilirubin, vitamin D and calcium come from the same draw, and without gamma-GT ALP cannot be read.
Which tests include ALP?
ALP is in the Biological age test (€69, also as an add-on for €15), in the Liver function test (€59, also as an add-on for €15) and in .
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): alkaline phosphatase. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): alkaline phosphatase. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): alkaline phosphatase. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): alkaline phosphatase. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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