Evaluation of between-methods agreement of extracellular water measurements in adults and children.

BACKGROUND: Extracellular water (ECW), a relevant molecular level component for clinical assessment, is commonly obtained by 2 methods that rely on assumptions that may not be possible to test at the time the measurements are made. OBJECTIVE: The aim of the current study was to evaluate the degree of agreement between ECW assessment by the sodium bromide dilution (ECW(NaBr)) and total body potassium (TBK; whole-body (40)K counting) to total body water (TBW; isotope dilution) methods (ECW(TBK-TBW)) in an ethnically mixed group of children and adults. DESIGN: ECW was measured with the ECW(NaBr) and ECW(TBK-TBW) methods in 526 white and African American males and females (86 nonobese children, 193 nonobese adults, and 247 obese adults). Fat mass was assessed with dual-energy X-ray absorptiometry. Multiple regression analysis was used to examine the variables related to between-ECW method differences. RESULTS: Significant but generally small group mean (+/-SD) differences in ECW were found in the obese adults (1.28 +/- 2.54 kg) and children (-0.71 +/- 1.78 kg). The magnitude of the differences was related to mean ECW in obese adults, children, and nonobese adults, and the relations between these variables were modified by sex for nonobese adults. ECW differences were also dependent on age, weight, sex, and race or on interactions between these variables. CONCLUSIONS: Overall, although good between-method agreement was found across the 3 groups, the degree of agreement varied according to subject characteristics, particularly at the extremes of ECW and body weight. We advance a possible mechanism that may link subject characteristics with the degree of agreement between ECW measurement methods and their underlying assumptions.

Baseline characteristics of the randomised cohort from the Look AHEAD (Action for Health in Diabetes) study.

OBJECTIVE: The Look AHEAD (Action for Health in Diabetes) study is a 16-centre randomised clinical trial in overweight and obese individuals with type 2 diabetes, designed to evaluate the long-term effects (up to 11.5 years) of intensive weight loss intervention on the time to incidence of major cardiovascular events. RESEARCH DESIGN AND METHODS: Eligibility requirements are diagnosis of type 2 diabetes (determined by self-report and verification) in individuals aged 4574 years and body mass index (BMI) > 25 kg/m2 (> 27 kg/m2 if currently taking insulin). The intensive lifestyle intervention is designed to achieve and maintain weight loss through decreased caloric intake and increased physical activity. The study is designed to provide 90% probability of detecting an 18% difference in major cardiovascular disease event rates in patients randomised to the intensive lifestyle intervention compared to the control group receiving standard diabetes support and education. RESULTS: The 5,145 participants who were randomised between 2001 and 2004 were 63.3% white, 15.6% African-American, 13.2% Hispanic, 5.0% American Indian and 1.0% Asian-American, which closely paralleled the ethnic distribution of diabetes in the National Health and Nutrition Examination Survey (NHANES) 1999-2000 survey. Their average age at entry was 59+/-6.8 years (mean+/-SD), and 60% were women. There were 31.5% between 4555 years of age, 51.5% were 5665, and 17.0% were 6676 years of age. Some 15.4% of participants were taking insulin at the time of randomisation and 14.0% had a history of cardiovascular disease. More men (21.3%) than women (9.2%) had a history of cardiovascular disease. Few participants (4.4%) were current cigarette smokers, compared to 16.2% in the NHANES 1999-2000 survey. Furthermore, 65.0% of participants had a first-degree relative with diabetes. Overall, BMI averaged 36+/-5.9 kg/m2 at baseline, with 83.6% of the men and 86.1% of women having a BMI > 30 kg/m2 and 17.9% of men and 25.4% of women having a BMI > 40 kg/m2. CONCLUSIONS: The Look AHEAD study has successfully randomised a large cohort of participants who have type 2 diabetes with a wide distribution of age, obesity, ethnicity and racial background and will examine the effects of lifestyle intervention on the incidence of major cardiovascular events.