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Test ID: BAP Bone Alkaline Phosphatase, Serum

Reporting Name

Bone Alkaline Phosphatase, S

Useful For

Diagnosis and assessment of severity of metabolic bone disease including Paget disease, osteomalacia, and other states of high bone turnover


Monitoring efficacy of antiresorptive therapies including postmenopausal osteoporosis treatment


The assay is not intended as a screening test for osteoporosis.


Measurements of bone turnover markers are not useful for the diagnosis of osteoporosis; diagnosis of osteoporosis should be made based on bone density.

Clinical Information

Bone alkaline phosphatase (BAP) is the bone-specific isoform of alkaline phosphatase. A glycoprotein that is found on the surface of osteoblasts, BAP reflects the biosynthetic activity of these bone-forming cells. BAP has been shown to be a sensitive and reliable indicator of bone metabolism.(1)


Normal bone is constantly undergoing remodeling in which bone degradation or resorption is balanced by bone formation. This process is necessary for maintaining bone health. If the process becomes uncoupled and the rate of resorption exceeds the rate of formation, the resulting bone loss can lead to osteoporosis and, consequently, a higher susceptibility to fractures.


Osteoporosis is a metabolic bone disease characterized by low bone mass and abnormal bone microarchitecture. It can result from a number of clinical conditions including states of high bone turnover, endocrine disorders (primary and secondary hyperparathyroidism and thyrotoxicosis), osteomalacia, kidney failure, gastrointestinal diseases, long-term corticosteroid therapy, multiple myeloma, and cancer metastatic to the bones.(2)


Paget disease is another common metabolic bone disease caused by excessive rates of bone remodeling resulting in local lesions of abnormal bone matrix. These lesions can result in fractures or neurological involvement. Antiresorptive therapies are used to restore the normal bone structure.


Bone alkaline phosphatase (BAP) concentration is high in Paget disease and osteomalacia.(3)


Antiresorptive therapies lower BAP from baseline measurements in Paget disease, osteomalacia, and osteoporosis. Several studies have shown that antiresorptive therapies for management of osteoporosis patients should result in at least a 25% decrease in BAP within 3 to 6 months of initiating therapy.(4,5) BAP also decreases following antiresorptive therapy in Paget disease.(6)


When used as a marker for monitoring purposes, it is important to determine the critical difference (or least significant change). The critical difference is defined as the difference between 2 determinations that may be considered to have clinical significance. The critical difference for this method was calculated to be 25% with a 95% confidence level.(1)

Report Available

2 to 3 days

Day(s) Performed

Monday through Saturday

Clinical Reference

1. Kress BC: Bone alkaline phosphatase: methods of quantitation and clinical utility. J Clin Ligand Assay. 1998;21(2):139-148

2. Kuo TR, Chen CH: Bone biomarker for the clinical assessment of osteoporosis: recent developments and future perspectives. Biomark Res. 2017 May;5:18. doi: 10.1186/s40364-017-0097-4

3. Sharma U, Pal D, Prasad R: Alkaline phosphatase: an overview. Indian J Clin Biochem. 2014 Jul;29(3):269–278. doi: 10.1007/s12291-013-0408-y

4. Kress BC, Mizrahi IA, Armour KW, et al: Use of bone alkaline phosphatase to monitor alendronate therapy in individual postmenopausal osteoporotic women. Clin Chem. 1999 Jul;45(7):1009-1017

5. Garnero P, Darte C, Delmas PD: A model to monitor the efficacy of alendronate treatment in women with osteoporosis using a biochemical marker of bone turnover. Bone. 1999 Jun;24(6):603-609

6. Raisz L, Smith JA, Trahiotism M, et al: Short-term risedronate treatment in postmenopausal women: Effects on biochemical markers of bone turnover. Osteoporos Int. 2000;11:615-620

Method Name

Immunoenzymatic Assay

Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.6 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days
  Frozen  90 days
  Ambient  7 days

Reference Values


<2 years: 25-221 mcg/L

2-9 years: 27-148 mcg/L

10-13 years: 35-169 mcg/L

14-17 years: 13-111 mcg/L

Adults: ≤20 mcg/L



<2 years: 28-187 mcg/L

2-9 years: 31-152 mcg/L

10-13 years: 19-177 mcg/L

14-17 years: 7-41 mcg/L


Premenopausal: ≤14 mcg/L

Postmenopausal: ≤22 mcg/L

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
BAP Bone Alkaline Phosphatase, S 17838-4


Result ID Test Result Name Result LOINC Value
BAP Bone Alkaline Phosphatase, S 17838-4
Mayo Clinic Laboratories | Endocrinology Catalog Additional Information:

mml-bone-minerals, mml-diabetes-metabolic-nutrition