Test Catalog

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 in serum consists of 4 structural genotypes: the liver-bone-kidney type, the intestinal type, the placental type, and the variant from the germ cells. It occurs in osteoblasts, hepatocytes, leukocytes, the kidneys, spleen, placenta, prostate, and the small intestine. The liver-bone-kidney type is particularly important. 


A rise in the alkaline phosphatase occurs with all forms of cholestasis, particularly with obstructive jaundice. It is also elevated in diseases of the skeletal system, such as Paget disease, hyperparathyroidism, rickets and osteomalacia, as well as with fractures and malignant tumors. A considerable rise in the alkaline phosphatase activity is sometimes seen in children and juveniles. It is caused by increased osteoblast activity following accelerated bone growth.

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.


0-14 days: 83-248 U/L

15 days- <1 year: 122-469 U/L

1-<10 years: 142-335 U/L

10-<13 years: 129-417 U/L

13-<15 years: 116-468 U/L

15-<17 years: 82-331 U/L

17-<19 years: 55-149 U/L

> or =19 years: 40-129 U/L



0-14 days: 83-248 U/L

15 days-<1 year: 122-469 U/L

1-<10 years: 142-335 U/L

10-<13 years: 129-417 U/L

13-<15 years: 57-254 U/L

15-<17 years: 50-117 U/L

> or =17 years: 35-104 U/L

Interpretation Provides information to assist in interpretation of the test results

Increases in serum alkaline phosphatase (ALP) activity commonly originate from 1 or both of 2 sources: liver and bone. Consequently, serum ALP measurements are of particular interest in the investigation of 2 groups of conditions: hepatobiliary disease and bone disease associated with increased osteoblastic activity.


Serum ALP was the first enzyme to be used for the investigation of hepatic disease. The response of the liver to any form of biliary tree obstruction induces the synthesis of ALP by hepatocytes. The newly formed coenzyme is released from the cell membrane by the action of bile salts and enters the circulation to increase the enzyme activity in serum. Increase tends to be more notable (greater than 4-fold the upper reference value [URV]) in extrahepatic obstruction (eg, by stone, 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 URV and usually return to baseline on surgical removal of the obstruction. A similar increase is seen in patients with advanced primary liver cancer or widespread secondary hepatic metastases. ALP increase (greater than 2-fold the URV) can predict transplant-free survival rates of patients with primary biliary cirrhosis.


Liver diseases that principally affect parenchymal cells, such as infectious hepatitis, typically show only moderately (less than 3-fold) increased or even normal serum ALP activities. Increases may also be seen as a consequence of a reaction to drug therapy, and ALT/ALP-based criteria to discriminate the type of liver injury in drug-induced hepatic toxicity have been recommended. Intestinal ALP isoenzyme, an asialoglycoprotein normally cleared by the hepatic asialoglycoprotein receptors, is often increased in patients with liver cirrhosis.

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

1. Rifai N, Horvath AR, Wittwer C: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics 2018;29:404-434

2. Abicht K, El-Samalouti V, Junge W, et al: Multicenter evaluation of new GGT and AlP reagents with new reference standardization and determination of 37 degrees C reference intervals. Clin Chem Lab Med 2001;39: Special Supplement pp S 346

3. Estey MP, Cohen AH, Colantonio DA, et al: CLSI-based transference of the CALIPER database of pediatric reference intervals from Abbott to Beckman, Ortho, Roche and Siemens Clinical Chemistry Assays: Direct validation using reference samples from the CALIPER cohort. Clin Biochem 2013;46:1197-1219

4. Lammers WJ, van Buuren HR, Hirschfield GM, et al: Levels of alkaline phosphatase and bilirubin are surrogate end points of outcomes of patients with primary biliary cirhosis: an international follow-up study. Gastroenterology 2014; 147: pp. 1338-1349