Bone Alkaline Phosphatase, Serum (LAB1070)

Bone Alkaline Phosphatase (b-ALP) testing is most useful in patients with normal creatinine and gamma-glutamyl transferase (gGT), when alkaline phosphatase (ALP) is elevated with no apparent cause.

Clinical Background
  • ALP is present in all tissues, particularly concentrated in the liver, bile duct, kidney, bone, intestine, and placenta. In the serum, elevated ALP concentrations are commonly associated with liver damage, bone disorders, and/or chronic kidney disease. 
Common Pitfalls
  • b-ALP is a send-out test that is often unnecessarily ordered when the elevation in total ALP has a plausible explanation, leading to additional costs for the hospital and/or patients.
  • The normal reference interval for b-ALP in adults is ≤20 mcg/L. Therefore, b-ALP cannot be used to assess low b-ALP.
  • b-ALP should not be ordered when liver ALP is elevated. Liver ALP has cross-reactivity in the bone ALP assay: 100 U/L of liver ALP activity increases b-ALP 2.5 – 5.8 mcg/L.
Key Takeaways
  • b-ALP is reflected in total ALP. b-ALP should not be ordered when total ALP is normal. 
  • If the total ALP is elevated, creatinine and gGT should be measured to determine its source.
  • Osteoporosis treatment is best monitored using the in-house tests for osteocalcin and cross-linked C-telopeptide of type I collagen (CTX), including in patients treated with Prolia (denosumab).  
  • In patients with chronic kidney disease, total ALP & parathyroid hormone (PTH) can be used to evaluate bone disease. The BJH PTH assay is unaffected by renal failure.
References
  1. Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017 Jan;112(1):18-35.
  2. Bauer D et al. National Bone Health Alliance Bone Turnover Marker Project: current practices and the need for US harmonization, standardization, and common reference ranges. Osteoporos Int. 2012 Oct;23(10):2425-33.
  3. Eastell R et al. Effects of denosumab on bone turnover markers in postmenopausal osteoporosis. J Bone Miner Res. 2011 Mar;26(3):530-7.
  4. KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) Kidney International 2009;76 (Suppl 113):S212-S130. 

Written by: Nick Spies, MD

Reviewed by: Ann M. Gronowski, PhD

Last Edited: 2024-06-18

Last Reviewed: 2024-06-18