Biomedical subjects
F Blyth
Publications and source records attributed to F Blyth.
Body mass index in screening for adiposity in children and adolescents: systematic evaluation using receiver operating characteristic curves.
Body mass index (BMI) has been recommended for use in adolescent screening programs to select subjects with excess body fat for appropriate interventions. No systematic evaluation of MBI in screening for high degrees of adiposity was available when these recommendations were formulated. The purpose of this paper was to evaluated the screening performance of BMI using appropriate epidemiologic methods. Percentage body fat (TBF%) was measured by dual-energy X-ray absorptiometry DXA) in a convenience sample of 230 (119 males, 111 females) health Australian volunteers aged 4-20 y inclusive. Receiver operating characteristic (ROC) curves were prepared for detecting TBF% at or beyond the 85th percentile, using BMI as the screening test. Screening performance was slightly better for girls than for boys, but the differences were not significant. Reasonable true-positive (0.71, 95% CI: 0.53, 0.85) and low false-positive (0.05, 95% CI: 0.02, 0.09) rates were observed at the 85th percentile cutpoint for BMI. At the 95th percentile cutpoint for BMI, both true-positive (0.29, 95% CI: 0.15, 0.47) and false-positive (0.01, 95% CI: 0.00, 0.03) rates were lower. Screening for excess adiposity by using an appropriate percentile cutoff for BMI gives acceptable performance. ROC curves facilitate design of screening programs by allowing an explicit tradeoff between true-positive and false-positive rates. Although large sample sizes are required for precise estimates, the cutoff points that have been recommended appear to offer a reasonable compromise between true-and false-positive rates.
Adiposity and body mass indices in children: Benn's index and other weight for height indices as measures of relative adiposity.
OBJECTIVES: Several forms of weight for height or body mass index (BMI) are in widespread epidemiological and clinical use as measures of relative adiposity. The form derived by Benn for adults has been advocated for use in children and practical aspects of this proposition are considered. METHODS: Height and weight data from 8492 Australian schoolchildren aged 7 to 15 were studied. A subsample of 2753 children aged 9, 12 and 15 years had skinfold thicknesses measured. The sum of four skinfolds and percentage body fat predicted from skinfolds were used as measures of adiposity. RESULTS: Of the various forms of power type BMI examined, weight/(height)2 was most closely associated with adiposity in this sample. Benn's assumption of low correlation between height and adiposity (which holds in adults) was not satisfied in children. CONCLUSIONS: Benn's index is not recommended for general use as a body mass index in children. However, Benn's relative weight has advantages as an indirect measure of adiposity which may be of value in epidemiological studies among children.
Recommended body mass index cutoff values for overweight screening programmes in Australian children and adolescents: comparisons with North American values.
OBJECTIVE: Guidelines for screening children and adolescents for overweight have recently been published by a North American Expert Committee. As Australian clinicians might uncritically adopt these recommendations, we explore the consequences of applying North American body mass index (BMI) cutoff values to an Australian population. METHODOLOGY: The Australian BMI cutoffs were calculated using the methods recommended from height and weight data for 8492 schoolchildren aged 7-15 years old. RESULTS: Smoothed Australian BMI cutoffs were similar to those derived from the first United States National Health and Nutrition Examination Survey (NHANES-I) values for whites. However, the NHANES-I cutoffs would result in systematic misclassification. Among 7 year olds, the NHANES-I 85th percentile cutoff would wrongly classify 4.6% of normal males and 9.1% of normal females as 'at risk of overweight'. At age 14 years, the NHANES-I 95th percentile cutoff would misclassify 3.5% of children as 'overweight' instead of 'at risk of overweight'. CONCLUSION: Australian screening programmes should use BMI cutoffs appropriately derived from local measurements, and these are given for Australian children.
Smoking in child family day care homes: policies and practice in New South Wales.
OBJECTIVES: To provide estimates of the numbers of New South Wales children in Family Day Care who may be exposed to environmental tobacco smoke while attending day care; to describe existing smoking policies; and to analyse these policies with the aim of providing guidelines for smoking policy in Family Day Care. SETTING: All 109 Family Day Care schemes in NSW. METHOD: Scheme coordinators were sent a questionnaire regarding the proportion of carers who smoked while caring for children; the nature, enforcement and experience of smoking policies; and barriers to implementation of a no-smoking policy. RESULTS: A mean of 10% of Family Day Care caregivers were reported to smoke while caring for children (range, 0-60%). An estimated 2045 children were potentially exposed to environmental tobacco smoke in the 86 schemes which provided this information. Thirty-five per cent of schemes had formal no-smoking policies. A range of advantages, disadvantages and perceived practical and legal barriers to implementation of a no-smoking policy in Family Day Care were described. Forty-four per cent of schemes with no-smoking policies reported no implementation problems. CONCLUSIONS: There is considerable potential for exposure of children to environmental tobacco smoke in Family Day Care homes. There is legal support for Family Day Care caregivers not to expose children under their care to environmental tobacco smoke. A formal (and enforced) no-smoking policy should exist in every Family Day Care scheme, and a "top-down" directive is most likely to be successful. The issue of other smokers in the caregiver's household needs to be specifically addressed in any such directive.
Failure to detect brain reactivity of lymphocytotoxins in cerebral lupus.
Lymphocytotoxic activity (LCA) was examined in the sera of 29 patients with systemic lupus erythematosus (SLE), including eight with cerebral involvement. LCA was elevated in 80% of samples and was significantly higher in the group with cerebral disease (P less than 0.001). No correlations were observed between LCA and immune complexes or complement components. Sera from 10 patients (six with cerebral SLE) were absorbed with homogenates of normal human frontal cortex and liver using protein standards to control for dilutional effects. No serum sample showed selective depletion of LCA following incubation with brain homogenate. It is concluded that no single parameter, including brain absorption of LCA, is effective in monitoring disease activity in cerebral lupus.