ALP (alkaline phosphatase) is an enzyme that mainly reflects what’s happening in your liver, bile ducts, and bones. In adults, a high value can involve bile flow or bone metabolism, and a low value can involve nutrition, medications, thyroid function, and more. In growing children, a higher value can be natural. In Japan, the way ALP is measured began changing in April 2020, and values are now about a third of what they used to be, so take care when comparing them with older checkup results.
What ALP reflects
ALP is an enzyme that removes phosphate from substances that have phosphate attached. It’s found in many places in the body, including the liver and bile ducts, the osteoblasts that build bone, the small intestine, the kidneys, and the placenta during pregnancy. In adults, the ALP that shows up in the blood comes mainly from the liver and bile ducts, and from bone.
Bile is made in the liver and flows through the bile ducts into the duodenum, the first part of the small intestine. When that flow backs up, the liver and bile ducts make more ALP, which then enters the blood. ALP from osteoblasts also rises in the blood during times when bone is being actively built. ALP itself doesn’t move bile along; it’s a marker that reflects how bile is flowing and how bone is being rebuilt.
The ALP on your results is the sum of ALP from these different sources. When it’s important to know whether it’s coming from the liver or from bone, clinics can run an “ALP isoenzyme” test.
Japan changed the method in April 2020, and values dropped to about a third
For many years, ALP in Japan was measured with the “JSCC method,” set by the Japan Society of Clinical Chemistry (JSCC). It was decided to switch to the international “IFCC method,” and starting in April 2020, facilities switched over one after another as they became ready. The timing varies from facility to facility.
Here’s how the two compare in Japan’s shared reference intervals (JCCLS):
| Method | When it was used | Adult reference range | Precision nutrition optimal range |
|---|---|---|---|
| JSCC method | Until March 2020 (at some facilities, until around 2021) | 106–322 U/L | — |
| IFCC method | From April 2020, facility by facility | 38–113 U/L (same for men and women) | 63 U/L (a single point, not a range) |
The right-hand column shows the precision nutrition optimal range I use in my counseling. This is a precision nutrition guide, not a medical reference range. For adult ALP, it’s meant for values measured with the current IFCC method, so I don’t apply it to results from before the switch (JSCC method). Being above or below it doesn’t by itself mean you have an illness or are short on a nutrient.
One reason for the switch was that the JSCC method reacted strongly to ALP from the small intestine. In people with blood type B or O who have the “secretor” trait, this tended to produce high values unrelated to any illness (said to be most noticeable after a high-fat meal).
When you look at your actual results, check the following:
- Whether the test name has a label like “ALP(IFCC)” next to it. Even without one, you can tell from the reference range column: around 38–113, or around 106–322.
- When you line up results from before the switch (those with a reference range of around 106–322), multiplying the old value by 0.35 gives a rough comparison. This is a guide from the Japan Society of Clinical Chemistry, and it can be off when there’s a lot of ALP from the small intestine or the placenta.
- A change like “it used to be in the 200s, and suddenly it’s in the 70s” is often a change in the method, not a change in your body.
LD (LDH) also switched to the IFCC method around the same time, but its reference range stayed the same, and values in healthy people are nearly unchanged (in liver disease and some other cases, they can come out 10–20% lower).
“High” means something different for children and adults
Higher values are often natural in children
Because children’s bones are still growing, they have a lot of ALP from osteoblasts in their blood. In infancy and early childhood, and again around puberty, it isn’t unusual for ALP to be several times the adult reference range. It then moves toward the adult range in the late teens. Children’s reference ranges are set separately by age and sex. In Japan, ranges built from data on Japanese children can be converted to IFCC values using a factor provided by the Japan Society of Clinical Chemistry.
In babies and toddlers, there’s also a known pattern called “transient hyperphosphatasemia,” in which ALP climbs very high for a while, unrelated to any illness, and settles down within a few months. In a U.S. study of 316 healthy children aged 8 months to 2 years, about 3% had ALP above 1,000 U/L (measured with a method close to the one now used in Japan). Please leave the assessment to a pediatrician.
On the other hand, if a child’s ALP is low for their age, nutrition or a rare inherited disorder (hypophosphatasia, which I’ll touch on later) could be involved, so it’s reassuring to talk it over with a pediatrician.
What a high ALP can mean in adults
When an adult’s ALP is above the reference range, the question is whether it’s coming from the liver and bile duct side or from the bone side.
Bile isn’t flowing well
ALP goes up when bile flow backs up because of gallstones, inflamed bile ducts, bile duct diseases such as primary biliary cholangitis, liver disease or tumors, the effects of medications you’re taking, and so on. In that case, GGT (γ-GTP) often rises along with it, and total bilirubin may rise too.
Bone is being rebuilt more actively
Bone-derived ALP can also increase during recovery from a fracture, and with an overactive parathyroid or thyroid, chronic kidney disease, cancer that has spread to the bone, or a long-lasting lack of vitamin D that keeps bone from mineralizing properly. What sets this apart is that GGT often stays within the reference range.
Temporary factors
During pregnancy, ALP from the placenta increases as the weeks go by, so values run higher. Placental ALP reacts more readily in the IFCC method, so the actual value can come out higher than an estimate made by multiplying an old-method value by 0.35. For people with blood type B or O who are secretors, having blood drawn after a meal still has some effect. It’s smaller now, but it hasn’t gone away.
In every case, the ALP number alone can’t pin down the cause. If it’s several times the reference range, or other markers are moving along with it, it’s important to have a doctor check whether any of the illnesses above are involved.
What a low ALP can mean
Even when ALP is below the lower limit of the reference range, checkups often don’t flag it. Still, possible reasons for ALP staying low include undernutrition, a lack of vitamins or minerals, hormonal disorders, medications, and inherited disorders.
- Not enough food or protein: ALP can run low with extreme dieting or after rapid weight loss.
- Low zinc: ALP is an enzyme that contains zinc, so it can run low when zinc is short. However, the Japanese Society of Clinical Nutrition’s “Clinical Practice Guideline for Zinc Deficiency 2024” removed low ALP from its criteria, noting that ALP doesn’t drop in many people who are low in zinc. Zinc status is assessed from serum zinc (an early-morning, fasting blood draw is considered best) together with what the person is experiencing.
- Low magnesium: Magnesium is another mineral involved in how ALP works, and it’s been suggested that a shortfall could have an effect, but the evidence in humans is limited.
- Lower thyroid function: When the thyroid slows down and bone turnover slows with it, ALP can run low (see Thyroid: TSH, FT3, and FT4).
- Medications: Drugs that hold back bone turnover, such as osteoporosis medications, can make ALP run low.
- Hypophosphatasia: An inherited disorder caused by changes in the gene that makes ALP (ALPL); in Japan, it’s on the national list of designated intractable diseases. It can weaken bones and teeth. Severe forms are rare, and the forms found in adults are often said to be mild.
How I read the numbers
What follows isn’t a medical standard. It’s the way I read blood data, from a precision nutrition perspective.
Where you sit within the reference range
The reference range of 38–113 U/L is the span that most healthy people fall within. It isn’t a line where inside means no problem and outside means illness. Beyond whether a value is inside or outside the range, I look at whether it leans toward the lower end or the upper end. The range is the same for men and women, but JCCLS’s detailed tables put the upper limit for women 45 and older at 123 U/L (93 U/L for women under 45). After menopause, bone turnover speeds up and values tend to run higher, so I take age and sex into account as well.
I also compare where a value sits within the range against the optimal range in the table above.
For adults whose values keep landing near the lower limit, I look back with them on whether they’re getting enough food, protein, and zinc, alongside what they eat and how they’ve been feeling (changes in taste, rough skin, cuts that take a long time to close, and so on). ALP can’t settle the question of low zinc, so I use it only as one cue to notice, and I check zinc status with serum zinc. When values sit near the upper limit, or have risen since last time, I check the liver and bile duct markers, and whether there’s a bone-related life stage or event.
Reading it alongside other markers
Because ALP comes from more than one source, reading it in combination with other markers tells you more.
| Marker to read with ALP | Example of how to read it |
|---|---|
| GGT (γ-GTP) | If it’s high along with ALP, consider the liver and bile duct side. If only ALP is high and GGT is within the reference range, consider the bone side, too. |
| AST and ALT | If they stand out more than ALP, consider the liver cells; if ALP stands out more, consider bile flow. |
| Total bilirubin | If it’s high along with ALP, put bile flow first and have a doctor check it. |
| TSH and FT4 | If ALP runs low and you keep feeling sluggish or cold, have a doctor check the thyroid markers, too. |
| Age and life stage | Values tend to run higher during the growing years, in pregnancy, after a fracture, and after menopause. |
What you can revisit in everyday life
Zinc and magnesium from food
Zinc is plentiful in shellfish such as oysters, in liver and other meats, and in cheese, nuts, and sesame seeds. Magnesium is a mineral that’s easy to get from seaweed, beans, nuts, and less-refined grains. Guideline amounts for each age and sex are given in the Dietary Reference Intakes for Japanese (2025 edition) from Japan’s Ministry of Health, Labour and Welfare.
Too much zinc can get in the way of copper absorption, so if you take zinc as a supplement, don’t increase the amount on your own; talk with a doctor or another qualified professional.
Bile flow and weight changes
What I share here isn’t a way to lower ALP. These are general habits for keeping the gallbladder working well.
When a meal containing fat comes in, the gallbladder contracts and sends out bile. If you keep up a diet that strictly avoids fat, or a routine with very long gaps between meals, the gallbladder gets fewer chances to send bile out. There are times when spacing out your meals suits you, so I think it’s best to adjust as you go, comparing how you feel with your data.
If GGT is on the high side and ALP is within the reference range, it’s worth revisiting how much you drink (see GGT (γ-GTP)). If ALP is high as well, please first have a doctor check whether bile flow is backed up.
Rapid weight loss, and weight-loss diets that cut fat drastically, have been reported to make gallstones more likely. Extreme dieting can also be a reason ALP runs low, so it’s safer to take weight loss slowly.
Get tested the same way each time
Changes in values measured the same way tell you more than any single result. Getting tested in the morning on an empty stomach at the same clinic, and keeping notes on things like pregnancy, fractures, and medications you’re taking, makes comparisons easier.
If you’re concerned
In cases like these, please talk with a doctor soon (for example, an internist or a gastroenterologist):
- Your ALP is well above the reference range, or comes back high again and again
- GGT, AST and ALT, or total bilirubin is high as well
- Your skin or the whites of your eyes look yellow, your urine is dark, itching won’t go away, or you have pain in your upper right abdomen
If your ALP stays low and you have bone pain, fractures from minor injuries, or teeth falling out early, it’s also reassuring to talk with an internist or an endocrinologist.
If you’re under a doctor’s care or taking medication, please don’t stop your medication or change the dose on your own. Let’s revisit your diet and lifestyle step by step, talking things over with your doctor along the way.