ALP - Clinical: Alkaline Phosphatase, Serum

Test Catalog

Test Name

Test ID: ALP    
Alkaline Phosphatase, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing and monitoring treatment of liver, bone, intestinal, and parathyroid diseases

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Alkaline phosphatase (ALP) is present in a number of tissues including liver, bone, intestine, and placenta. Serum ALP is of interest in the diagnosis of 2 main groups of conditions-hepatobiliary disease and bone disease associated with increased osteoblastic activity.


A rise in ALP activity occurs with all forms of cholestasis, particularly with obstructive jaundice. The response of the liver to any form of biliary tree obstruction is to synthesize more ALP. The main site of new enzyme synthesis is the hepatocytes adjacent to the biliary canaliculi.


ALP also is elevated in disorders of the skeletal system that involve osteoblast hyperactivity and bone remodeling, such as Paget disease, hyperparathyroidism, rickets and osteomalacia, fractures, and malignant tumors. A considerable rise in alkaline phosphatase activity caused by increased osteoblast activity following accelerated bone growth is sometimes seen in children and juveniles.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


4 years: 149-369 U/L

5 years: 179-416 U/L

6 years: 179-417 U/L

7 years: 172-405 U/L

8 years: 169-401 U/L

9 years: 175-411 U/L

10 years: 191-435 U/L

11 years: 185-507 U/L

12 years: 185-562 U/L

13 years: 182-587 U/L

14 years: 166-571 U/L

15 years: 138-511 U/L

16 years: 102-417 U/L

17 years: 69-311 U/L

18 years: 52-222 U/L

> or =19 years: 45-115 U/L


4 years: 169-372 U/L

5 years: 162-355 U/L

6 years: 169-370 U/L

7 years: 183-402 U/L

8 years: 199-440 U/L

9 years: 212-468 U/L

10 years: 215-476 U/L

11 years: 178-526 U/L

12 years: 133-485 U/L

13 years: 120-449 U/L

14 years: 153-362 U/L

15 years: 75-274 U/L

16 years: 61-264 U/L

17-23 years: 52-144 U/L

24-45 years: 37-98 U/L

46-50 years: 39-100 U/L

51-55 years: 41-108 U/L

56-60 years: 46-118 U/L

61-65 years: 50-130 U/L

> or =66 years: 55-142 U/L

Reference values have not been established for patients that are <4 years of age.

Interpretation Provides information to assist in interpretation of the test results

The elevation in alkaline phosphatase (ALP) tends to be more marked (more than 3 fold) in extrahepatic biliary obstruction (eg, by stone or by cancer of the head of the pancreas) than in intrahepatic obstruction, and is greater the more complete the obstruction. Serum enzyme activities may reach 10 to 12 times the upper limit of normal, returning to normal on surgical removal of the obstruction.


The ALP response to cholestatic liver disease is similar to the response of gamma-glutamyltransferase (GGT), but more blunted. If both GGT and ALP are elevated, a liver source of the ALP is likely. Among bone diseases, the highest level of ALP activity is encountered in Paget disease as a result of the action of the osteoblastic cells as they try to rebuild bone that is being resorbed by the uncontrolled activity of osteoclasts. Values from 10 to 25 times the upper limit of the reference interval are not unusual. Only moderate rises are observed in osteomalacia, while levels are generally normal in osteoporosis. In rickets, levels 2 to 4 times normal may be observed. Primary and secondary hyperparathyroidism are associated with slight to moderate elevations of ALP; the existence and degree of elevation reflects the presence and extent of skeletal involvement. Very high enzyme levels are present in patients with osteogenic bone cancer. A considerable rise in ALP is seen in children following accelerated bone growth.


In addition, an increase of 2 to 3 times normal may be observed in women in the third trimester of pregnancy, although the interval is very wide and levels may not exceed the upper limit of the reference interval in some cases. The additional enzyme is of placental origin.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Pediatric reference values should be used to properly interpret alkaline phosphatase values in children and adolescents.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Tietz NW: Textbook of Clinical Chemistry. Third edition, Edited by Burtis and Ashwood. Philadelphia, PA, WB Saunders Company, Philadelphia, 1999.