Alkaline phosphatase: what it is, what it tells you and why we test it

Alkaline phosphatase, often ALP on your report, is a protein made mainly by your liver and your bones. Its level in your blood helps show whether bile is flowing well and how fast your bones are renewing. On its own, though, it does not say which of the two it comes from: that is why it is read with GGT.

Why we test it

In the liver, alkaline phosphatase sits in the bile ducts, the small channels that carry bile to the gut. If bile does not flow well, the number rises.

In bone, it is made by the cells that build new bone. When bone renews faster, for example while you grow or after a fracture, it rises too.

That is why a number outside the range is a useful signal: it points to the liver or to the bones. Other tests help tell which.

What it tells you, and what it does not

If it is high, your liver or your bones are usually making more of it. But the number alone does not say which: in adults, about half comes from bone.

GGT helps tell them apart. If it is high too, the liver or the bile is usually involved. If it is normal, bone is more likely.

If it is low, it is usually nothing to worry about. It is uncommon, and often comes from medicines or an illness.

That is why it is read together with other tests:

Normal alkaline phosphatase levels

The lab decides what is normal. It is usually 35 to 104 U/L for women and 40 to 129 for men. Your own report may print different limits, sometimes very different ones, because they depend on the lab’s method.

In teenagers who are still growing it can be much higher, because their bones are getting longer. Children and teenagers have limits of their own on the report.

In pregnancy it rises, above all in the last months, because the placenta makes it too. In women after menopause it can rise a little, because bone renews faster.

In the Rosa report you also see your optimal range, read together with GGT and your other liver tests.

What your result means

Find the row for your result, in U/L. If your report prints different limits, its limits count. Which values are dangerous? There is no single cut-off: what counts is your GGT and other tests, and whether you have symptoms. If it is high with no clear reason, show your report to your doctor.

If your alkaline phosphatase is high or low

What can skew the result

A few things change the number for a while. It helps to know them before you read it.

When to worry

Talk to your doctor if:

Frequently asked questions

What does ALP mean on my report? It is the abbreviation for alkaline phosphatase. On your report it usually sits next to the other liver tests: transaminases, GGT and bilirubin.

Low alkaline phosphatase: what does it mean? It is uncommon and usually nothing to worry about. More often it comes from medicines such as cortisone or some osteoporosis treatments, an illness, or a diet short of vitamins and minerals. Rarely it is an inherited condition called hypophosphatasia: with bone pain, fractures from small knocks or problems with your teeth, talk to your doctor.

Do I need to fast for an alkaline phosphatase test? It is better. After a fatty meal the number can rise for a few hours, and other tests in the same draw need fasting anyway. You can drink water.

Do the numbers change with age? Yes. In teenagers who are still growing it is much higher, and the report uses limits of its own. In adults it changes little, and in women after menopause it can rise a little.

How often should it be checked? For people who feel well there is no fixed rule: Rosa measures it twice a year. If it is out of range, your doctor decides whether to repeat it and which tests to add.

Sources