Alkaline phosphatase blood test: what high or low ALP means

What ALP measures

ALP is an enzyme found in many tissues. Most of the ALP in your blood comes from the liver, the bile ducts and the bones, with smaller amounts from the kidneys, intestines and, in pregnancy, the placenta. Each tissue makes its own form of the enzyme.

A standard ALP test adds all of these forms together. So a high number says something is making extra ALP, but not where. See the ALP lab guide and the liver function panel for how it fits with the other markers.

What a high ALP can mean

The liver and bone are the two main sources of a high ALP, but there are other reasons too:

• Liver and bile ducts. Blocked or narrowed bile ducts, hepatitis, cirrhosis, mononucleosis and cholestasis of pregnancy. ALP sits close to the bile channels, so bile flow problems often raise it most.
• Bone. Healing fractures, Paget's disease of bone, osteomalacia (soft bones, often from low vitamin D), an overactive parathyroid or thyroid, and cancer that has spread to bone.
• Normal reasons. Childhood and teen growth spurts and pregnancy raise ALP. Some medicines, including birth control pills, can shift it, and a fatty meal before the draw can nudge it up a little.
• Less common: untreated celiac disease, heart failure, some infections and Hodgkin lymphoma.

A mildly high result often is not a sign of disease. A clinician looks at how high it is, whether it stays high on a repeat test, and what the rest of your panel shows.

Liver or bone: how clinicians find the source

The usual next step is a GGT test. Liver and bile duct problems raise both ALP and GGT. Bone problems raise ALP but usually not GGT.

An ALP isoenzyme test can also split the total into liver and bone forms, but not every lab offers it. Read more in GGT blood test.

What a low ALP can mean

Low ALP is less common. It has been linked to:

• Low zinc or magnesium, or low protein and overall malnutrition
• An underactive thyroid
• Pernicious anemia
• Wilson disease
• Hypophosphatasia, a rare inherited bone condition

Gabriel's optimal floor of 45 U/L is a cue to look at diet, zinc and magnesium with your clinician, not a diagnosis.

What to do with an abnormal result

1. Read it with the rest of the panel. ALT, AST, bilirubin and GGT show whether the liver is involved.
2. Ask about GGT if it wasn't run, and about vitamin D if a bone source looks likely.
3. Bring your medication and supplement list. Some medicines raise or lower ALP. Don't stop anything unless your clinician says so.
4. Repeat the test if the rise is mild. Follow your lab's fasting instructions; many ask you to fast for several hours.
5. If you have a report in hand, you can upload it to Gabriel for a plain-words read of every marker, then take your questions to your clinician.

See a clinician promptly if a high ALP comes with yellow skin or eyes, dark urine, pale or clay-colored stools, pain in the upper right belly, unexplained weight loss, or new bone pain.