Jens Borg

Measurement of lean body mass and total body fat using dual photon absorptiometry

We describe a method for measuring the lean body mass (LBM) and total body fat (FAT) by dual photon absorptiometry (DPA). A total body rectilinear scan was employed with a radiation source of 1 Ci 153Gd. The reliability of estimating the lean percent was assessed in vitro using limb phantoms consisting of ox muscle, lard, and human bone. The precision and accuracy in vitro of the lean percent determination were 1.5% and 1.9%, respectively. The accuracy error in vivo of measuring the total mass of soft tissues (TMST) was approximately 1.4%, thus yielding an overall accuracy error of the LBM of about 2.5%. The precision in vivo of the lean percent and the LBM in kg of duplicate measurements on five healthy subjects was 2.5% and 2.2%, respectively. Other estimates of the LBM and FAT, ie, the calculation according to Boddy et al6 and the skinfold thickness measurement (triceps and subscapular), were compared to the DPA measurement in 100 healthy subjects. High correlations were found between the FAT or FAT% by DPA versus (1) the FAT or FAT% calculated according to the formulae of Boddy et al, and (2) the skinfold thickness. The correlations between the FAT and FAT% by Boddy et al and the skinfold thickness were, however, moderate. The correlation between LBM by DPA and LBM by Boddy et al was highly significant (r = 0.96, SEE = 4.4%). We conclude that LBM and FAT measurements using DPA have precision and accuracy errors that are commensurate with a reliable estimation of the gross body composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of the subcutaneous fat in the distal forearm by single photon absorptiometry

The influence of subcutaneous fat on single photon (125I) absorptiometry (SPA) measurement of bone mineral content of the distal forearm was investigated. A fat correction model was tested by measurements on eight lean subjects with different amounts of porcine fat around their forearm, and further validated from measurements on 128 females. In addition, it is shown that the fat content in the distal forearm can be measured by SPA with a short-term precision at 1.9% in an obese subject and that it correlates well with total body fat (r2 = .7) measured by dual photon absorptiometry, skinfold thickness (r2 = .5), and body mass index (r2 = .6). By using this method in a double-blind placebo-controlled trial, hormonal substitutional therapy significantly decreased the forearm fat content without affecting the body weight in postmenopausal osteoporotic women.

Representativity of regional to total bone mineral in healthy subjects and ‘anticonvulsive treated’ epileptic patients. Measurements by single and dual photon absorptiometry*

Abstract. Dual photon (153Gd) and single photon (125I) absorptiometry were used to measure the regional bone mineral content (BMC) and density (BMD), as well as the total body bone mineral content (TBBM) and density (TBBD), in sixty‐nine healthy subjects and in twenty‐three epileptics on phenobarbitone. The BMCs (and BMDs) of all regions were significantly correlated to each other and to the TBBM (and TBBD). No difference in the ability to discriminate between the different study groups was found for the various regions, excepting the BMD of the head. The relationship between the forarm BMC and TBBM was highly significant, and indentical in the five groups. The relationships between spinal BMC and forearm BMC, and TBBM differed in the five groups. It is concluded that some local measurement may be used as estimates of the total body bone mineral in some groups of patients with minor metablic bone disease and healthy subjects.

Peripheral bone densitometer

A. What is the evidence that peripheral systems detect osteoporosis and predict fractures? 1. Despite the fact that all the early work in the field was done using peripheral (mainly forearm) systems, the role of peripheral densitometry in the diagnosis and management of osteoporosis is controversial. 2. Facts: a. Output variables of peripheral systems are generally correlated with bone strength and BMD by central DXA. b. Peripheral systems can differentiate osteoporotic patients (with and without preexisting fractures) from normals. c. Peripheral systems can predict global fracture risk in postmenopausal women nearly as well as central DXA. B. Reality check: controlled clinical trials versus realworld use of peripherals. 1. Technical limitations affect utility. a. Ambient temperature, edema, foot size, injuries, etc. may confound measurements. b. Output variables differ among peripheral systems. c. Regions of interest differ among peripheral systems. d. Normative databases differ among peripheral systems. e. Diagnostic discrepancy exists among peripheral systems. f. Operation: generally no in-person, manufacturer-guided training. 2. T-scores from peripherals can be used to assess fracture risk but should not be used to make a diagnosis following World Health Organization criteria. a. T-score cutpoints vary among peripheral systems. b. Sensitivity and specificity of peripheral systems compared with central DXA for detecting osteopenia and osteoporosis generally does not meet International Society for Clinical Densitometry recommendations. c. Discordance with central DXA. 3. Results of most (but not all) studies suggest that peripherals should not be used to monitor patients on antiresorptive treatment. 4. Use with men and premenopausal women is commonplace but not well validated. 5. Lack of interpretation guidelines leads to confusion about what to do with results (eg, when should additional testing with central DXA be recommended?). 6. Reporting of results is often poorly done, especially in nonmedical settings. 7. Educational and wellness programs are good venues for use of peripheral systems.