Alkaline Phosphatase, Elevated
Judith A. Fisher and M. Gina Glazier
Alkaline phosphatase (ALP) is an enzyme expressed on the plasma membrane of many cells. It has two primary sources: the liver (specifically, the biliary tree) and bones (it marks new bone formation) (1). In adults, approximately half of the circulating ALP comes from the liver and the other half from bone. Small amounts are produced by the intestines and vascular endothelium. In pregnancy, significant amounts are produced by the placenta.
The range of normal serum ALP levels varies throughout life. Normal ranges are:
Infant: 50–165 U/L
Child: 20–150 U/L
Adult: 20–70 U/L
Adult aged more than 60 years: 30–75 U/L
Approach
A serum ALP should be ordered only if suspecting bone or liver disease. No role is seen for a “screening” or “routine” ALP. If the ALP level is found to be elevated, normal physiologic elevation owing to age or pregnancy should be excluded, along with spurious elevation caused by a recent albumin infusion (2), the use of an anticoagulant tube for the blood collection, or leaving the serum sample standing at room temperature for prolonged periods (increases the level by 30%). Recently, an ALP has been described that is produced by malignant tumors (“the Regan isoenzyme”), which closely resembles placental ALP.
Although a reasonable attempt can usually be made at estimating the source of elevated ALP, occasionally, it may be necessary to identify the isoenzymes biochemically. Heat inactivation and l-phenylalanine inhibition have been used. Placental and tumor ALP tend to be heat stable, whereas bone is heat labile. These tests are technically difficult and expensive and are rarely used. However, monoclonal antibodies are now being developed for this purpose and show promise (3).
Further testing should be done, based on the results of a careful history and physical examination, and be targeted to specific clinical suspicions (Table 17.1).
Other rarer causes of elevation include hyperthyroidism, vitamin D deficiency (particularly in the elderly and debilitated), hepatic infiltration (caused by lymphoproliferative disorders, granulomatous disease, or primary and secondary malignancies of the liver), and intestinal conditions such as bowel obstruction, and infarction. Because of the presence of ALP in the vascular system, infarction of any solid organ can cause ALP elevation.
References
1. Taylor AK, Lueken SA, Libanati C, Baylink DJ. Biochemical markers of bone turnover for the clinical assessment of bone metabolism. Clin Rheum Dis 1994;20:589–607.
2. Bark CJ. Albumin-induced elevation in alkaline phosphatase. JAMA 1971;216: 518–520.
3. Broyles DL, Nielsen RG, Bussett EM, Lu WD, Mizrahi IA, Nunnelly PA, et al. Analytical and clinical performance characteristics of Tandem-MP Ostase, a new immunoassay for serum bone alkaline phosphatase. Clin Chem 1998;44:2139–2147.
Pictures
Book Source Details
- Book Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter
- Author(s): Robert B. Taylor (editor)
- Year of Publication: 2000
- Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2000 Lippincott Williams & Wilkins.
Other Book Chapters Related to Increased intracranial pressure
Read excerpts from these other book chapters related to Increased intracranial pressure:
Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2008 Williams & Wilkins.
More About Causes of Increased intracranial pressure
» Next page:
ALKALINE PHOSPHATASE ELEVATION (Differential Diagnosis in Primary Care)
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
