Vol. 17 •Issue 1
• Page 70
Lab Limelight
Lab's Role in Osteoporosis
By Kelly J. Graham
An estimated 10 million Americans have osteoporosis, and another 34 million may have low bone mass, placing them at an increased risk for developing osteoporosis.1 This disease predominantly affects people over the age of 50, and the laboratory must be aware of its role in identifying and monitoring osteoporosis as the number of older Americans continues to increase.
The lab shares responsibility for osteoporosis monitoring and detection with various other healthcare providers. Bone mass measurements or bone mineral density tests are performed via imaging, for example, but lab tests remain vital for adjunct information (such as identifying underlying causes of osteoporosis) and to monitor efficacy of hormone replacement therapy when menopause or hormone deficiency is the cause of bone mass loss.
Specific Tests
Lab testing for osteoporosis aims to determine whether a patient has osteoporosis, has low bone mass and an increased risk of developing the disease, is menopausal or hormone-deficient, and/or has an underlying condition that may be causing or exacerbating bone loss. Tests may screen for bone density loss or determine bone status after an unexpected fracture and may be used to monitor the efficacy of osteoporosis therapy.
Bone formation tests include measurements of bone-specific alkaline phosphatase associated with osteoblasts and osteocalcin, a protein created by osteoblasts.
Bone resorption tests are urine tests that assist in determining if a patient is losing bone. Certain bone protein byproducts are released into the urine as bone breaks down; measuring the amount of these byproducts can identify the rate of bone break down. These tests include:
C-telopeptide (C-terminal telopeptide of type 1 collagen [CTx])—a fragment of the protein matrix;
N-telopeptide (N-terminal telopeptide of type 1 collagen [NTx])—another fragment of the protein matrix;
Deoxypyridinoline (DPD)—a collagen breakdown product; and
Pyridinium crosslinks—a group of collagen breakdown products, including DPD.2
NTx is the most specific marker of bone resorption, specific to type I collagen of bone, according to Dave Kolesar, ELISA marketing manager, Inverness Medical Professional Diagnostics. NTx is the only marker indicated to predict skeletal response to hormone replacement therapy in postmenopausal women, he explains. NTx can also determine the probability for decrease in bone mass in those postmenopausal women not on hormone replacement therapy.
Lab tests such as NTx are particularly valuable because they can determine the rate of bone loss that takes place during the interval between testing, as opposed to bone mineral density measurements via imaging, which give a static picture of a bone's density.
Associated Tests
A handful of lab tests associated with osteoporosis do not test specifically for bone density, loss or formation, but for underlying conditions that may be causing bone loss or low bone mass. Vitamin D deficiencies, for example, may lead to decreased calcium absorption, which negatively affects bone formation. Protein electrophoresis may be performed to identify abnormal proteins that can break down bone, produced by multiple myeloma. FSH or testosterone may be checked to identify menopause or hormone deficiency–both of which lead to increased risk of osteoporosis.
Proactive Role
Osteoporosis is both preventable and treatable. Though the number of Americans over the age of 50 is increasing, the number of osteoporosis diagnoses doesn't have to. Should you notice a potentially connected condition in a patient's test results that can be a marker of bone problems to come–particularly in patients over 50, and especially women–verify that the physician is aware of the result so that he might talk to the patient about simple lifestyle changes that can help prevent more bone mass loss.
Kelly J. Graham is assistant editor.
References
1. National Osteoporosis Foundation. Accessed at http://www.nof.org/osteoporosis/diseasefacts.htm
2. Lab Tests Online: Osteoporosis. Accessed at http://www.labtestsonline.org/understanding/conditions/osteoporosis-2.html
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