Alkaline phosphatase

Alkaline phosphatase
S -AFOS KL 1046

(in English S -ALP)

Alkaline phosphatase (ALP) is a hydrolase enzyme responsible for releasing phosphate from phosphate esters. As its name implies, it functions optimally in an alkaline environment. Different tissues have distinct isoenzymes with varying physicochemical properties, allowing for a separate isoenzyme study to investigate the enzyme’s tissue origin, if required.

In adults, the primary source of ALP enzyme is the liver, while in growing children, the main component is a bone isoenzyme.


The diagnosis and monitoring of liver and bile duct diseases, as well as bone-related conditions. Additionally, diagnosing increased osteoblast activity.


1.0 mL of serum (min. 0.5 mL). Hemolysis interferes with the assay.

Storage and delivery

The sample can be refrigerated for up to a week, but for longer storage, it should be kept frozen. Delivery at room temperature, if it arrives within 24 hours. Hemolysis interferes with the assay.


Photometric, in accordance with IFCC recommendation. Accredited method.

Turnaround time

1-2 weekdays

Reference ranges

Age (years)Girls/Adults (U/I)Boys/Adults (U/I)
1 – 5115 – 390115 – 390
6 – 7115 – 460115 – 460
8 – 9115 – 345115 – 345
10 – 11115 – 435115 – 335
12 – 1390 – 335125 – 405
14 – 1580 – 21080 – 445
16 – 1835 – 12555 – 330
over 1835 – 10535 – 105
The reference values for adults are established using the data from the reference value material published by Huslab (2014).

Interpretation of results

In humans, the alkaline phosphatase enzyme is produced in various tissues, including the liver, bile, bones, intestines, and, during pregnancy, in the placenta.

Elevated levels of ALP are commonly associated with biliary obstruction, which can either be extrahepatic (e.g., due to gallstones or pancreatic carcinoma) or intrahepatic (caused by blockages of small bile ducts, liver metastases, or certain drug intake). Acute hepatitis is also linked to significantly increased ALP values.

The bone-derived isozyme of ALP shows significant elevation in Paget’s disease and bone cancer tumors. A moderate increase in the enzyme is observed in conditions like bone metastases, hyperparathyroidism, rickets, and osteomalacia. To a lesser extent, ALP levels can rise in connection with bone fractures.

On the other hand, reduced ALP values are found in cases of hereditary enzyme deficiency and in connection with hyperthyroidism.


Last update 8.8.2023