Research Blog

September 13, 2023

Bone Alkaline Phosphatase is Specific

Bone-specific alkaline phosphatase (BSAP) is an isoenzyme of alkaline phosphatase found in the osteoblast cell membrane. It is used as a bone turnover marker to monitor significant changes in bone density. This blood-based marker can pick up changes earlier than a bone density scan. Levels are evaluated pre- and post-treatment to assess efficacy and bone density improvements (Pagana 2022).

Bone-specific alkaline phosphatase functions in an alkaline environment, a setting favorable to calcium crystallization and bone formation. An acidic environment favors osteoclast activity and bone resorption, which can be detrimental.

Serum levels of BSAP reflect osteoblasts' cellular activity and will increase with bone formation, growth, bone turnover, and bone fractures. Levels will also increase in pathological conditions, such as osteomalacia, rickets, Paget disease, osteoblastic bone lesions or osseous metastases, hyperparathyroidism, and hyperthyroidism.

Additional blood chemistries, including calcium, phosphorus, parathyroid hormone, thyroid stimulating hormone, renal function tests, and cancer screening, should accompany the evaluation of elevated serum BSAP. In general, decreased alkaline phosphatase levels may be associated with hypophosphatasia or nutrient insufficiencies, including magnesium, zinc, or vitamin C (Corathers 2006).

Evaluation of BSAP in 135 osteoporotic postmenopausal women found that mean serum BSAP was significantly higher in those with concurrent aortic calcification, suggesting a potential association (Iba 2004).

There is no ODX optimal range at this time for bone-specific alkaline phosphatase. Below are examples of conventional ranges:

Conventional ranges for BSAP, serum (mcg/L)

Mosby’s Diagnostic and Laboratory Test Reference (Pagana 2022)

  • Male: 6.5-20.1
  • Female, premenopausal: 4.5-16.9
  • Female, postmenopausal: 7-22.4

Quest Diagnostics


  • 18-29 years 4-29.3 mcg/L
  • 30-39 years 7-21.3 mcg/L
  • 40-49 years 0-18.3 mcg/L
  • 50-68 years 6-14.9 mcg/L
  • >68 years Not established


  • 18-29 years 7-17.8 mcg/L
  • 30-39 years 3-19.5 mcg/L
  • 40-49 years 0-18.8 mcg/L
  • 50-76 years 6-29.0 mcg/L
  • >76 years Not established
  • 35-45 years 0-18.2 mcg/L

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Corathers, Sarah D. “Focus on diagnosis: the alkaline phosphatase level: nuances of a familiar test.” Pediatrics in review vol. 27,10 (2006): 382-4. doi:10.1542/pir.27-10-382

Iba, Kousuke et al. “The serum level of bone-specific alkaline phosphatase activity is associated with aortic calcification in osteoporosis patients.” Journal of bone and mineral metabolism vol. 22,6 (2004): 594-6. doi:10.1007/s00774-004-0528-9

Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 16th ed., Mosby, 2022.

Quest Diagnostics. Bone-Specific Alkaline Phosphatase.


Tag(s): Biomarkers

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