Bone mass measurement by DXA: influence of analysis procedures and interunit variation.

Interunit variability among bone densitometers is due to different factors, including different calibration procedures and algorithms and variability in photon source energies and/or intensities. Other factors, such as the choice of scan parameters or the analysis procedures, can also introduce variability. The new generation of dual-energy x-ray absorptiometry (DXA) has partially improved this situation. The aim of this study was to investigate the operator-dependent analysis procedures that can affect scan results and to evaluate the phantom and in vivo interunit variation of some DXA instruments. Four DXA instruments (QDR 1000 and 1000/W, Hologic, Inc.) were used. Potential sources of variability in the analysis procedures of anteroposterior lumbar spine and hip scans were considered: in most cases these procedures significantly influenced scan results. On lumbar spine, an enlargement of the scan window of less than 3 cm was responsible for an average increase in bone mineral density (BMD) of about 3%. On the hip, lowering the scan window by about 1 cm accounted for an increase in the whole-segment BMD of about 4%. After standardization of analysis procedures, interunit and intraunit coefficients of variation and percentage differences among instruments were less than 1% for all the parameters considered (area and bone mineral content and density) with both an anatomic and a geometric phantom, and in nine subjects scanned by two different devices the percentage difference in BMD was greater than 2%. This study shows that present interunit variability allows comparisons among laboratories, but only if highly standardized analysis procedures are used.

Bone mineral metabolism in juvenile chronic arthritis: the influence of steroids.

Calciotropic hormone assays and bone mineral density (BMD) evaluations were carried out on a group of 36 children affected with juvenile chronic arthritis (JCA) (13 with pauciarticular, 8 with polyarticular and 15 with systemic onset subtype) and in a matched control group. The plasma levels of calcium, phosphate and alkaline phosphatase were normal in all the groups. Basal 25-OH D plasma levels were significantly decreased both in the polyarticular and in the systemic groups; the latter showed a further decrease after 1 year. There was a significant decrease in both the basal and the 1-year plasma levels of 1-25-OH D only in the systemic group. The BMD was decreased in the systemic group alone and the percentage increase after 1 year was significantly inferior to that in the other groups and in the controls. There was a clear relationship between the decrease in hormones and the cumulative dose of steroids administered, as well as between the BMD decrease and the physical activity of the patients (according to Steinbrocker's classification).

Vitamin D metabolites in spasmophilia.

The comparison of 20 untreated spasmophilic patients (2 men, 18 women) with 25 healthy subjects revealed no significant differences in vitamin D metabolite plasma levels or in other laboratory indexes of calcium metabolism except for ionized and cytosolic free calcium levels which were lower in the former group (P less than 0.01; P less than 0.001). After 3 months treatment with calcitonin and 25-hydroxyvitamin D there was a clear improvement in patient symptoms, no significant modification of 1,25-dihydroxyvitamin D levels and significant increases in 25-hydroxyvitamin D, cytosolic free calcium and urinary calcium (P less than 0.001, P less than 0.001 and P less than 0.01, respectively). We conclude that high plasma levels of 25-hydroxyvitamin D play an important role in restoring normal cytosolic free calcium levels and reducing clinical manifestations in spasmophilia.

Bone mineral density in adult celiac patients and the effect of gluten-free diet from childhood.

Peripheral single photon absorptiometry was used to measure forearm bone mineral density in 22 celiacs on gluten-free diet from childhood (male 14, female 8, age 13-20) and 29 untreated adult celiacs at diagnosis (male 5, female 24, age 18-56, 14 with subclinical disease), compared with healthy sex- and age-matched controls. Bone mineral density was similar in patients treated from childhood and their controls [(668.4 +/- 65.3 vs. 654.9 +/- 69.6 mg/cm2, (mean +/- SD)], but significantly lower in untreated patients than in their controls (598.3 +/- 83.1 vs 673.2 +/- 42.7 mg/cm2, p less than 0.001). It was also significantly lower in the 12 younger untreated celiacs (18-28 yr) versus controls (619.4 +/- 68.5 vs 669.1 +/- 39.3 mg/cm2, p less than 0.01). In the untreated women, but not their controls, a negative correlation (p less than 0.05) was observed between bone mineral density and age. Bone mineral density did not correlate with severity of clinical or biochemical abnormalities. These results suggest that bone derangements are common in celiacs diagnosed in adulthood, even if they never presented evident malabsorption symptoms, and emphasize the importance of early diagnosis and treatment.