ALP Isoenzymes Blood Test (Alkaline Phosphatase)

The ALP isoenzymes blood test helps find out where a raised alkaline phosphatase (ALP) level is coming from. ALP is an enzyme found mainly in the liver and bones, with smaller amounts from the intestine and, during pregnancy, the placenta. Each source makes a slightly different form of the enzyme, called an isoenzyme.

A standard liver function test measures only total ALP. If your total ALP is raised, this test separates it into its different forms, showing whether the rise comes mainly from the liver, bone or another source. This helps your doctor decide which further tests are needed.

What the test measures
- Total alkaline phosphatase (ALP)
- The proportion from each source: liver, bone, intestinal and, where present, placental ALP

Why it matters
A raised ALP has many possible causes, from bile duct blockage and liver disease to bone conditions such as Paget's disease or vitamin D deficiency. Knowing which isoenzyme is raised helps narrow down the cause. A raised bone ALP is normal in growing children and teenagers, and placental ALP rises normally during pregnancy. Please discuss your result with your GP, who can decide whether any further tests are needed.

Alkaline Phosphatase Isoenzymes
- Total alkaline phosphatase (ALP)
- Liver isoenzyme (L-ALP)
- Bone isoenzyme (B-ALP)
- Placental isoenzyme (PL-ALP)
- Intestinal isoenzyme (I-ALP)
- Other or unusual isoenzyme fractions

No special preparation required.

For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.