Dual-energy X-ray absorptiometry diagnostic discordance between Z-scores and T-scores in young adults.

Diagnostic criteria for postmenopausal osteoporosis using central dual-energy X-ray absorptiometry (DXA) T-scores have been widely accepted. The validity of these criteria for other populations, including premenopausal women and young men, has not been established. The International Society for Clinical Densitometry (ISCD) recommends using DXA Z-scores, not T-scores, for diagnosis in premenopausal women and men aged 20-49 yr, though studies supporting this position have not been published. We examined diagnostic agreement between DXA-generated T-scores and Z-scores in a cohort of men and women aged 20-49 yr, using 1994 World Health Organization and 2005 ISCD DXA criteria. Four thousand two hundred and seventy-five unique subjects were available for analysis. The agreement between DXA T-scores and Z-scores was moderate (Cohen's kappa: 0.53-0.75). The use of Z-scores resulted in significantly fewer (McNemar's p<0.001) subjects diagnosed with "osteopenia," "low bone mass for age," or "osteoporosis." Thirty-nine percent of Hologic (Hologic, Inc., Bedford, MA) subjects and 30% of Lunar (GE Lunar, GE Madison, WI) subjects diagnosed with "osteoporosis" by T-score were reclassified as either "normal" or "osteopenia" when their Z-score was used. Substitution of DXA Z-scores for T-scores results in significant diagnostic disagreement and significantly fewer persons being diagnosed with low bone mineral density.

DXA-generated Z-scores and T-scores may differ substantially and significantly in young adults.

Central dual-energy X-ray absorptiometry (DXA) is the gold standard for non-invasive measurement of bone mineral density (BMD). Using this value and subject demographics, DXA software calculates T-scores and Z-scores. Professional society guidelines for the management of osteoporosis are based on T-scores and Z-scores, rather than on the actual BMD value. Although one expects T-scores and Z-scores to be very similar in young men and women for any given BMD measurement, little literature exists on this issue. Our clinical experience shows that some younger adult individuals (premenopausal women and men younger than 50 yr) have larger than expected difference between their DXA T-score and Z-score. This cross-sectional study evaluates the extent of this discordance between Z-scores and T-scores in a sample of 4275 men and women aged 20-49 yr. All subjects were scanned by central DXA using equipment manufactured by GE Lunar, GE, Madison, WI, or Hologic, Inc., Bedford, MA. Significant differences between Z-scores and T-scores were seen within individuals at the lumbar spine, total hip, femoral neck, and trochanter (p value<0.001) for both DXA systems. Although these differences were less than half a standard deviation (SD) in most instances, the magnitude of difference was substantial at times, being 1 or more SD in up to 11% of cases (range: -1.95 to +1.54 SD). The smallest differences were seen at the total hip and the largest differences were seen at the femoral neck for both technologies. This is in part because there is no single standard Z-score definition, resulting in different methods of calculation across, and even within, DXA manufacturers. Standardization of Z-score definition and method of calculation is indicated. DXA Z-scores should be interpreted with caution in men and women aged 20-50 yr.

Utility of DXA for monitoring, technical aspects of DXA BMD measurement and precision testing.

Monitoring a patient's bone mineral density (BMD) is one of the main reasons for dual-energy X-ray absorptiometry (DXA) referral. It is widely recommended by clinical guidelines, and the accepted standard in practice for managing patients with osteoporosis and other disorders. Clinicians and DXA providers must be familiar with the scientific rationale and procedures involved in measurement science to obtain accurate and reproducible results. Their importance is critical to maximise the value of scan acquisition and interpretation. Scanning individual patients, with different needs and disorders, requires excellence in training, experience, and is more complex than just simply 'measuring BMD'. Over the past 3 decades many studies have validated the importance of monitoring BMD for fracture risk assessment, and for patients on osteoporosis treatment. New DXA features enhance the value of DXA monitoring today. Quality BMD measurement remains an essential component of patient care in osteoporosis and other disorders, playing a critical role in informed decision making for clinicians assessing and managing their patients. In this article we describe some of the technical aspects of measurement and discuss the utility of DXA for monitoring patients in clinical practice.

Strategies for the prevention and treatment of osteoporosis during early postmenopause.

During the perimenopause, both the quantity and quality of bone decline rapidly, resulting in a dramatic increase in the risk of fracture in postmenopausal women. Although many factors are known to be associated with osteoporotic fractures, measures to identify and treat women at risk are underused in clinical practice. Consequently, osteoporosis is frequently not detected until a fracture occurs. Identification of postmenopausal women at high risk of fracture therefore is a priority and is especially important for women in early postmenopause who can benefit from early intervention to maintain or to increase bone mass and, thus, reduce the risk of fracture. Most authorities recommend risk-factor assessment for all postmenopausal women, followed by bone mineral density measurements for women at highest risk (ie, all women aged > or =65 years, postmenopausal women aged <65 years with > or =1 additional risk factors for osteoporosis, and postmenopausal women with fragility fractures). All postmenopausal women can benefit from nonpharmacologic interventions to reduce the risk of fracture, including a balanced diet with adequate intake of calcium and vitamin D, regular exercise, measures to prevent falls or to minimize their impact, smoking cessation, and moderation of alcohol intake. Several pharmacologic agents, including the bisphosphonates (eg, alendronate, risedronate, and ibandronate) and the selective estrogen receptor modulator, raloxifene, have been shown to increase bone mass, to reduce fracture risk, and to have acceptable side-effect profiles. Women who have discontinued hormone therapy are in particular need of monitoring for fracture risk, in light of the accelerated bone loss and increased risk of fracture that occurs after withdrawal of estrogen treatment.

Bone density changes with once weekly risedronate in postmenopausal women.

Risedronate 5 mg daily is approved by the Food and Drug Administration to treat postmenopausal osteoporosis. Gastrointestinal (GI) symptoms are common with daily bisphosphonates, but recent studies show that once weekly treatment may be better tolerated. Risedronate 30 mg is approved to treat Paget s disease of bone. In this retrospective study, we assessed the GI tolerability of 30 mg of risedronate once weekly and evaluated the effect on bone mineral density (BMD) in a subset of women. Review of patients treated in our osteoporosis clinic identified 150 postmenopausal women with low BMD treated with 30 mg of risedronate once weekly, between February 1998 and March 2001. Baseline GI symptoms or previous intolerance of bisphosphonates was present in 32 patients. An additional antiresorptive treatment was continued with risedronate in 50% of these patients (estrogen, raloxifene, or calcitonin). Risedronate 30 mg was taken once weekly with vitamin D 400 iu daily and 1200 mg of calcium daily. Patient age ranged from 46 to 86 yr. Baseline and followup BMD data were available in 36 patients. Of the 32 patients with baseline GI symptoms or previous intolerance of a bisphosphonate, 1 developed GI symptoms. In those patients with baseline and follow-up BMD results (n = 36), BMD increased 1.9% (p = 0.02) at the trochanter and 2.1% (p = 0.001) at the total hip. In conclusion 30 mg of risedronate once weekly increased BMD at the trochanter and total hip (p < 0.05). This dosage was well tolerated with a low incidence of GI side effects.