Empeiria

Alkaline phosphatase

Also known as ALP, alk phos, alkaline phosphatase

enzyme activity · no single molecular formula

LOINC 6768-6 code verified serum U/L

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

An enzyme that comes from two main places: the drainage tubes of the liver, and bone. That shared origin is why a raised result on its own does not say which.

Membrane-bound hydrolase present in biliary epithelium, osteoblasts, placenta and intestine. The circulating pool is predominantly hepatic and skeletal.

why measured unverified

It flags problems with bile drainage, and separately picks up bone conditions.

It flags problems with bile drainage, and separately picks up bone conditions.

No clinical version written yet.

if high unverified

Either bile is not draining properly, or bone is unusually active. A second test called GGT tells the two apart: raised with it means liver, normal with it means bone.

Either bile is not draining properly, or bone is unusually active. A second test called GGT tells the two apart: raised with it means liver, normal with it means bone.

No clinical version written yet.

caveats unverified

Normally high in growing children and in pregnancy. Neither is a problem.

Normally high in growing children and in pregnancy. Neither is a problem.

No clinical version written yet.

What this substance is

Measured as catalytic activity rather than mass. ALP is additionally a family of isoenzymes from liver, bone, intestine and placenta that the routine assay does not separate, so even the protein identity is plural.
What it catalyses

EC 3.1.3.1

a phosphate monoester + H2O = an alcohol + phosphate

Requires zinc, magnesium.

The reaction the test times
4-nitrophenyl phosphate, the lab's test substrate
→
4-nitrophenol, yellow: its colour is what the analyser reads

Each molecule is drawn from ChEBI's curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Atom diagrams are checked against the NIST Atomic Spectra Database.

3D model

4-nitrophenyl phosphate, the lab's test substrate. Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm with a needle. It usually takes less than five minutes. This test is often done with other blood tests, so you may need to skip food and drink for several hours. A fatty meal before the test can raise the result a little.

Serum or plasma (lithium, ammonium or sodium heparin) from venipuncture; other anticoagulants are not acceptable. Separated serum or plasma should be removed from cells within one hour of collection. Because ALP is usually ordered with other tests, patients usually fast for several hours; a fatty meal beforehand may cause a small increase in ALP.

Before the test

  • Fast (no food or drink) for several hours if your provider asks, since ALP is usually ordered with other blood tests.
  • Tell your provider about everything you take, but do not stop any medicine unless your provider tells you to.

Where: laboratory

Sources: Alkaline Phosphatase, MedlinePlus (U.S. National Library of Medicine); NHANES 2017-2018 Laboratory Procedure Manual, Alkaline Phosphatase (CDC National Center for Health Statistics) cited · not yet checked by a person

In the lab

kinetic enzyme

IFCC p-nitrophenyl phosphate

The enzyme is given a colourless substance that it turns into a coloured one. How quickly the colour appears is the measurement.

Hydrolysis of p-nitrophenyl phosphate releases coloured p-nitrophenol; the rate of its appearance gives the activity.

  • Read by: Rate of absorbance increase as p-nitrophenol forms (read at 450 nm on the Roche analyser NHANES uses)
  • Standardised to: IFCC, 37 °C, AMP buffer
Why labs disagree: Different buffers change the measured activity, so a result is only comparable against a range generated with the same buffer. Ranges are also genuinely higher in children, from fast bone growth, and in pregnancy, when the placenta adds its own form of the enzyme. These reflect real enzyme activity rather than an artefact.

Sources: Comparison of Analytical Values after Changing to the International Standardized Method for Lactate Dehydrogenase and Alkaline Phosphatase Measurements (2022), PMC open access; NHANES 2017-2018 Laboratory Procedure Manual: Alkaline Phosphatase (ALP), CDC/NCHS cited · not yet checked by a person

What it reports on

Associated symptoms

When high

Conditions this marker features in

When high
  • high Blocked or slowed bile flow · defining
    A raised ALP, mostly together with a raised GGT, is the lab sign of cholestasis. One national guideline (Chinese Society of Hepatology, 2021) sets the cut-off at ALP above 1.5 times the upper limit of normal plus GGT above 3 times.
  • high High blood calcium · supportive
    Often raised in primary hyperparathyroidism, the most common cause, and falls after surgery.
  • high Low vitamin D · supportive
    Raised once the deficiency affects bone (rickets or osteomalacia). Vitamin D deficiency is a common cause of an isolated raised ALP.
  • high Overactive thyroid · supportive
    Often raised in untreated hyperthyroidism, from faster bone turnover.
Either direction

Ordered as part of

cmp · hepatic