Alkaline Phosphatase (ALP)
ALP is a protein found in both your liver and your bones, so a raised result does not automatically mean a liver problem — it can just as easily come from busy bone. Your GP uses your other markers to tell the two apart. Many of the causes are common and settle on their own.
Standard CareWhat is alkaline phosphatase (alp)?
Alkaline phosphatase (ALP) is an enzyme — a protein that speeds up chemical reactions — that is involved in a wide range of processes and is found in many parts of the body, particularly the liver and bones, with smaller amounts in the intestines. Within the liver, ALP is especially high in the cells that line the bile ducts — the small tubes that carry bile (a digestive fluid) out of the liver. This dual origin — liver and bone — is the key thing to understand about ALP. A raised ALP is not automatically a liver signal; it can come from bone activity just as readily. Your GP uses GGT (gamma-glutamyl transferase) to tell them apart: a high ALP with a high GGT points towards the liver or bile ducts; a high ALP with a normal GGT can point towards bone. ALP is usually measured as part of Liver Function Tests (LFTs) — a standard panel that also includes ALT (alanine aminotransferase), AST (aspartate aminotransferase), GGT, albumin, and bilirubin.
Why is it tested?
Your GP may include ALP in a liver panel for several reasons. Most often it is to check general liver and bile duct health during a routine screen. It also helps when looking into symptoms such as jaundice (a yellowing of the skin or the whites of the eyes), itching, or abdominal pain. Because ALP comes from bone as well, it is also used to look at bone conditions such as Paget's disease (a disorder causing abnormal bone remodelling). And it can help pin down the source of a raised bilirubin or another off-key liver marker, or keep track of a known liver, bile duct, or bone condition over time.
Reference range (Australia)
The AACB/RCPA Australasian Harmonised Reference Intervals specify a single adult interval of 30–110 U/L without a sex split. The range printed on your own report is the authoritative figure for your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A low ALP result is rarely a concern in adults. Your GP will consider it alongside the rest of your LFT panel and clinical picture. In some circumstances a very low ALP may prompt further consideration, but this is uncommon.
An in-range ALP result is generally reassuring. Your GP reads it alongside the rest of the LFT panel to build the complete picture of liver and bone health.
A raised ALP means there is increased activity of ALP-producing cells — which can come from the liver, bile ducts, or bones. When the bile ducts are blocked — for example through scarring, gallstones, previous surgery, or by a tumour — ALP may be increased much more than either AST or ALT. Any condition that affects bone growth or causes increased activity of bone cells can also affect ALP blood levels. Because ALP comes from both the liver and bone, your GP will look at GGT alongside it. If GGT is also raised, the liver or bile ducts are the more likely source. If GGT is normal, bone causes become more likely. A wide range of conditions can move ALP — liver disease and bile duct blockages on one side, conditions affecting bone growth on the other, plus infections and gut disorders. A mildly raised ALP with a normal GGT can be entirely due to bone activity — something your GP can reassure you about and, if needed, investigate further with bone-specific tests.
What can affect your result
ALP can be raised by both liver/bile duct and bone causes. On the liver side: bile duct blockage (from gallstones, tumours, or scarring) typically raises ALP markedly; liver inflammation from viral hepatitis or fatty liver disease raises it more modestly; alcohol-related liver disease and certain medications can also elevate ALP. On the bone side: rapid bone growth (which is why ALP is normally higher in children and adolescents), bone healing after a fracture, Paget's disease (a disorder of abnormal bone remodelling), and other conditions causing increased bone cell activity can all raise ALP in the absence of any liver problem. Pregnancy is another common cause of a raised ALP, as the placenta produces its own form of the enzyme. GGT (gamma-glutamyl transferase) helps distinguish the source: a raised GGT alongside raised ALP points towards the liver or bile ducts; a normal GGT with a raised ALP suggests a bone origin.
When to act
A raised ALP is worth a conversation rather than alarm — it is not automatically a cause for concern. Your GP will look at GGT first to decide whether to follow the liver and bile duct trail or the bone trail. The rest of the LFT panel, any symptoms, and your overall health context all feed into that decision. Depending on the pattern, your GP may organise a repeat ALP test, request a bone-specific ALP fraction, arrange an ultrasound of the liver and bile ducts, or check for bone conditions with additional tests. If your other liver markers (ALT, AST, bilirubin, albumin) are also abnormal, a liver cause becomes more likely and your GP will focus their attention there. A raised ALP with normal GGT and normal other liver markers — particularly after growth, pregnancy, or a recent bone injury — can often be explained without any underlying disease. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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