LABORATORY TESTS

For an uncomplicated patient with osteoporosis, a laboratory workup would include a chemistry panel, complete blood count, and 24-hour urine calcium. ² Males should have testosterone levels 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. 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. ³,⁴ 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 performed whenever a patient presents with new fractures. ³ 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 an important cause 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 suggested.

Vitamin D and parathyroid hormone levels are expensive tests. Mild vitamin D deficiency may occur 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, vitamin D and parathyroid hormone levels should be performed.

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