Alkaline Phosphatase (ALP) Heat Stability Test

What is this test?

The Alkaline Phosphatase (ALP) heat stability test measures the portion of ALP enzyme that remains active after heating a blood sample. ALP is an enzyme found in various tissues, particularly the liver, bones, intestines, and kidneys. The heat-stable fraction primarily comes from the liver, while the heat-labile fraction comes from bones and intestines. This test helps doctors determine whether an elevated ALP level is due to liver disease or bone disorders.

Why is this test performed?

Your healthcare provider may order this test if a routine ALP test shows elevated levels. The heat stability test helps identify the source of the elevated enzyme. It is commonly used to: diagnose liver diseases such as hepatitis or cirrhosis; detect bile duct obstruction or gallstones; identify bone disorders including Paget's disease or bone metastases; and monitor the effectiveness of treatments for liver or bone conditions.

How is the test performed?

A healthcare professional will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory where it is heated to a specific temperature (typically 56°C or 65°C) for a set period. The heat-labile (heat-sensitive) portion of ALP is destroyed during this process, while the heat-stable portion remains. The remaining ALP activity is measured and reported. The procedure is quick and generally causes minimal discomfort.

What do the results mean?

Results are typically reported as a percentage of total ALP that is heat-stable, or as a specific activity level. A higher percentage of heat-stable ALP suggests liver as the source of elevated enzyme, while a lower percentage suggests bone involvement. Your doctor will interpret these results in conjunction with other liver function tests (such as ALT, AST, GGT, and bilirubin) and your overall clinical condition to make an accurate diagnosis.