Remember that not all fractures are osteoporotic. The differential diagnosis of fractures includes:
Many of these may be diagnosed from radiographs, bone scans, or magnetic resonance imaging studies. Sometimes bone biopsies are necessary.
Patients with decreased bone density usually have no specific abnormal physical findings. Those with vertebral compression fractures will have kyposis, protruding abdomen and height loss. Back tenderness is usually only present after an acute fracture. Gait speed and grip strength are often reduced in patients who have or are about to have a hip fracture. Visual acuity should be checked in geriatric patients because it is a risk factor for falling.
Secondary causes of osteoporosis may be associated with physical findings, such as nodular thyroid, hepatic enlargement, cushingoid features, skin rashes, jaundice, abnormal dentition, and findings of hypogonadism.
Sometimes decreased bone density ("demineralization") can be detected by xray, but bones can appear normal despite loss of 30% of bone mineral. On the other hand, bones in over-exposed films can appear demineralized when they aren't. Bone density measurements are much more accurate than xrays in determining bone density.
The "Singh index" of the proximal femur correlates with bone density. The trabeculae of the femur are lost in sequence, depending on the physical stresses to the bone, so the remaining trabecular pattern indicates the severity of bone loss.
Fractures are discussed in the clinical description page.
| Test | Charge |
|---|---|
| Chemistry panel | $57 |
| Serum calcium | $22 |
| 24hr urine calcium | $22 |
| Serum phosphate | 20 |
| Creatinine | $18 |
| Magnesium | $25 |
| Alkaline phosphatase | $22 |
| CBC | $21 |
| TSH | $43 |
| Testosterone | $61 |
| 25OH vitamin D | $61 |
| PTH, intact | $94 |
| N-telopeptide | $49 |
| Bone-specific alk.phos. | $?? |
| Protein electrophoresis | $?? |
For an uncomplicated patient with osteoporosis, a lab workup would be a chemistry panel, CBC, phosphate, TSH and 24-hour urine calcium. Males should have testosterone measured. The main purpose of laboratory tests is to check for secondary causes of osteoporosis such as cases of renal or hepatic failure, anemia, acidosis, hypercalciuria, and abnormalities of calcium/phosphate. A nice paper by Tannenbaum, C. documents the utility of these kind of blood tests.
Alkaline phosphatase is an inexpensive method of checking for osteoblastic activity. It is not as sensitive or specific as newer "bone markers" but it will detect moderate to severe osteomalacia or Paget's disease.
The 24-hour urine calcium measurement is frequently ignored but it is a valuable and inexpensive test. High levels are seen in idiopathic hypercalciuria, and low levels suggest malabsorption. The test should be done on a patient's customary calcium intake.
Protein electrophoresis should be done whenever a patient presents with new fractures. Both serum and urine tests should be done because some patients with myeloma have abnormalities in only one.
Corticosteroid excess that causes osteoporosis can usually be detected clinically by Cushingoid features. A urine cortisol can be helpful in puzzling cases.
Gonadal hormones are very important causes of osteoporosis. In females who are postmenopausal, it is not helpful to measure levels of estrogens or gonadotropins. In males, however, testosterone levels should be measured because there is much greater variability in the prevalence of hypogonadism. Also, men may have low testosterone without other clinical symptoms. If testosterone is low, then further work-up is needed.
Vitamin D and parathyroid hormone levels are expensive tests. Some physicians order them routinely, but the expense does not seem justified. Mild vitamin D deficiency frequently occurs in the absence of hypocalcemia, but if vitamin D supplementation is routinely given, it is not necessary to perform this test in patients with normal calcium. Primary hyperparathyroidism nearly always causes hypercalcemia. Secondary hyperparathyroidism may occur with normal calcium, but most of these cases will be detected by low urine calcium or decreased renal function. In patients with abnormal serum calcium or with unusually severe bone disease, however, the 25-OH-vitamin D and parathyroid hormone levels should be measured.
The 25 OH-vitamin D is more useful than the 1,25 (OH)2 vitamin D level. In fact, there are VERY FEW reasons to ever measure the 1,25(OH)2 vitamin D levels! If your patient needs this test, you probably should refer him or her to a specialist. Check out this page about vitamin D levels .
Bone specific biochemical markers are discussed on the next page.
Over the last decade there have been many debates about screening bone density. Several organizations have performed detailed cost-benefit studies and developed guidelines; these must be continually revised as new findings about treatment effects are discovered (U.S. Preventive services Task Force, American Association of Clinical Endocrinologists, National Osteoporosis Foundation). Bone density tests carry no physical risks, but there is a problem of over-interpretation of results, so that healthy ordinary average people think they are at a much higher risk than they actually are. In 2000 an NIH consensus conference concluded: "Until there is good evidence to support the cost-effectiveness of routine screening, or the efficacy of early initiation of preventive drugs, an individualized approach is recommended."
This is my personal list, following the principle that a physician should order a test only if he or she plans to change therapy as a result:
| Patients with risk factors or conditions that cause osteoporosis |
|---|
|
| Post-menopausal women |
| Women within ten years of menopause may decide to take estrogens if their bone density is low, especially since estrogen seems to be most effective at preventing hip fractures when started close to menopause. Women over age 65 could still have osteoporosis without other risk factors, and in that case medications would be beneficial. |
| Young patients with a non-traumatic fracture |
| For example, if a patient suffered a fracture from uncertain trauma, the measurement can be used to "rule out" osteoporosis as a cause. If the bone density shows strong bone (WHO category of normal), then a bone scan should be done to check for pathologic lesions or malignancy |
| "Demineralization" on an xay in young patients |
| Standard radiographs are not very accurate methods of detecting change in bone mineral. Demineralization on a routine xray may be the first sign of osteoporosis, or it may represent an over-exposed film. This indication is more appropriate in a young person, since all elderly people have some degree of bone loss. |
| Baseline evaluation for patient with fragility fracture |
|
Patients with vertebral compression fractures or hip fractures should usually have a baseline bone density measurement to help evaluate subsequent therapy. This is not as straightforward as it first appears, however. Some therapies that
significantly reduce fractures may not cause signficant improvement in bone density when measured in an individual patient. More studies are needed to provide evidence that follow-up bone density examinations are really helpful. Physicians must also be aware of the reproducibility of the density machines.
In elderly women with established osteoporosis, it is reasonable to start therapy without getting a bone density. It is unlikely that important future therapies will depend on knowing the bone density. In younger women, however, new therapies may be developed a decade from now, and it may be helpful to know the bone density response to treatment available now. |
