Description
Alkaline Phosphatase (ALP) is a ubiquitous enzyme associated with cell membranes and is encoded by 4 human genes: tissue-nonspecific, intestinal, germ cell and placental ALP iso-enzymes. Approximately 95% of circulating total ALP is derived from the bone and liver isoforms of the tissue-nonspecific isoenzyme, differing only in the degree of post-translational sialylation and glycosylation .
Bone ALP constitutes about 40% of serum total ALP in health. It is produced by osteoblasts to provide a high PO4 concentration at the osteoblast cell surface during bone mineralization and is a marker of bone formation.
Clinical Use
Bone-Specific Alkaline Phosphatase (BSALP) can be used to monitor response to antiresorptive therapy, confirm patient compliance and assess efficacy of new therapies in patients with metabolic bone disease such as osteoporosis, Paget’s disease (where total ALP is not informative), primary hyperparathyroidism and metastatic bone disease
BALP may be an appropriate bone marker to use in renal bone disease when other bone markers are affected by renal clearance.
Comments and interpretation
Single measurements of BALP are of limited value. A blood sample should be taken at baseline and 3 months after starting treatment to monitor response to therapy or disease progression. The least significant change between samples taken at 3 month intervals is +/ 30%.
BALP is a marker of bone formation, and so response to antiresorptive therapy lags behind the suppression observed with resorption markers by several weeks.
Use of BALP may be compromised in liver disease due to 8-15% cross-reactivity with liver isoform.
BALP levels may remain elevated for up to 6-9 months following healing of bone fractures.
Paediatric samples and young adults: Specific age-related reference ranges are not available but BALP levels are higher in children and in young adults, especially during the pubertal growth spurt (9-13 y girls, 11-16y boys) when BALP levels up to 4-5 times the adult range may be expected.
Sample requirements: Serum
Sample volume: 1.0 mL
Specimen Requirements: None. A baseline pre-treatment measurement is required if assessing response to antiresorption therapy
SAS Centres providing BALP:
- Norfolk & Norwich University Hospital Bone Marker Service
- Sheffield NGH Bone Markers Unit
- London Imperial Charing Cross Hospital Bone Marker Service