26590 Bone Alkaline Phosphatase, Serum (BAP)

​Alkaline Phosphatase​; Bone; BAP; Phosphatase; Skeletal Alkaline Phosphatase

​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.

Gross hemolysis

​Assay results should only be used in conjunction with information available from the clinical evaluation of the patient and other diagnostic procedures.

In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results and the laboratory should be alerted if the result does not correlate with the clinical presentation.

Liver-derived alkaline phosphatase (ALP) has some cross-reactivity in this assay: 100 U/L of liver ALP activity gives a result of 2.5 mcg/L to 5.8 mcg/L. Accordingly, serum specimens with significant elevations of liver ALP activity may yield elevated results.

​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.

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.

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.

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. BAP also decreases following antiresorptive therapy in Paget disease.

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.