BONE ALKALINE PHOSPHATASE (BAP) IN SERUM

CLINICAL UTILITY:

Serum levels of BAP are believed to reflect the metabolic status of osteoblasts. An accurate assessment of bone metabolism is critical for determining the severity of metabolic bone disease and responses to therapy. Measurement of serum levels of sALP has been shown to be useful in evaluating patients with Paget's disease, osteomalacia, primary hyperparathyroidism, renal osteodystrophy, osteoporosis and metastases to bone. Total alkaline phosphatase determinations have been the accepted method for the diagnosis and monitoring of patients with Paget's disease.

Paget's disease of bone is a common skeletal disorder in which there is a focal proliferation of the normal cellular components of bone. Paget's disease is more prevalent than once thought with the prevalence rate in certain populations 3%-4% in middle-aged patients and 10%-15% in the elderly. This disease does not affect young individuals. The majority of patients with Paget's disease have no symptoms and often go undiagnosed unless an abnormal X-ray or serum alkaline phosphatase level is found in the course of a medical evaluation for unrelated reasons. The most common complaints in symptomatic patients are pain and deformity.

The risk of osteoporosis, another bone remodeling disorder, depends in part upon skeletal development, the attainment of peak bone mass, and in later life, the amount of bone lost. In healthy children, bone formation is favored over bone resorption, which results in bone development and normal skeletal growth. In healthy young adults, bone formation and bone resorption are balanced, resulting in no net increase or decrease in skeletal mass. With advancing age, men and women experience and imbalance in bone remodeling in which resorption is slightly greater than formation, resulting in a continuous net loss of bone mass with time. If this imbalance persists, bone mass may decline until the skeleton is insufficient to withstand normal mechanical stresses, and it become abnormally susceptible to fractures. The excessive loss of bone mass with an increased susceptibility to fractures is a disorder known as osteoporosis.

The most common form of osteoporosis occurs in postmenopausal women and is the result of estrogen deficiency. Rapid bone loss accompanies the decline of estrogen levels at the onset of menopause or as a result of surgical removal of the ovaries. Rapid bone loss occurs as a result of the combined effects of imbalance in bone remodeling and an increase in bone turnover. In the United States, osteoporosis affects some 25 million postmenopausal women and is the cause of approximately 1.5 million fractures annually, including approximately 500,000 vertebral crush fractures, 250,000 hip fractures, and 200,000 distal radius fractures.

Hormone replacement therapy is currently the most widely prescribed therapy for the prevention of osteoporotic fractures in postmenopausal women. However many women cannot, or will not, avail themselves of hormone replacement therapy because of the potential for the increased risk of cancer and the resumption of menstrual bleeding. For this reason, other compounds such as bisphosphonates, a standard treatment for Paget's disease of bone, have been developed to treat osteoporosis. The anti-resorptive properties of bisphosphonates decrease bone remodeling and, consequently, decrease the overall loss of bone.

Biochemical markers are useful in monitoring metabolic bone disease. Urinary hydroxyproline and total serum alkaline phosphatase have been used for monitoring the treatment of Paget's disease. Osteoporosis, however, represents a more subtle modification of the bone resorption process; therefore, more specific and sensitive markers are needed.

Osteomalacia is the term used to describe a pathological condition in bone in which the osteoid matrix (the proteinaceous scaffolding in bone) remains uncalcified. The most common condition causing osteomalacia is vitamin D deficiency, resulting in rickets in children or osteopenia with bone fractures in adults. Elevated serum alkaline phosphatase is a hallmark of this condition. Recent data suggests that mild degrees of vitamin D deficiency may be very common in the population, and could contribute to osteopenia in patients diagnosed with osteoporosis.

METHOD DESCRIPTION:

Bone Alkaline Phosphatase (BAP) in Serum is measured by immunochemiluminescence.

REFERENCE RANGE:

Male = 3.7-20.9 ug/L; Premenopausal female = 2.9-14.5 ug/L;Postmenopausal female = 3.8-22.6 ug/L

SPECIMEN REQUIREMENTS:

1.0 ml (minimum 0.5 ml) sample is required for the assay. Serum and plasma (lithium heparin and sodium heparin) are the recommended sample types.