EAL

H/A: Body Composition Measurement (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the ability of bioimpedance analysis to estimate changes in body cell mass as measured by whole body counting of total body potassium.

Inclusion Criteria:

HIV-positive subjects
Healthy, weight-stable controls.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

Independent sample of volunteers. Body composition studies were performed in the Body Composition Unit at St. Luke's-Roosevelt Hospital Center between 1988 and 1996. The results of all complete body composition studies in a database containing more than 700 HIV-infected subjects and more than 800 healthy controls were reviewed.

Design

Longitudinal case-control study. Paired studies of body cell mass, including both total body potassium and bioimpedance analysis, were compared in HIV-positive subjects and healthy, weight stable controls.

Statistical Analysis

The association between predicted change in body cell mass by bioimpedance analysis and its estimation by total body potassium was determined by least squares linear regression in the HIV-infected group
Descriptive statistics of the observed errors in prediction were analyzed by T-test
The differences between body cell mass change by total body potassium and by bioimpedance analysis were plotted as a function of their average, as described by Bland and Altman
Potential sources of error in the estimation of change in body cell mass by bioimpedance analysis in the HIV-infected group were analyzed.

Data Collection Summary:

Timing of Measurements

Normal subjects were studied twice within two years and weight changed by less than 2.5%
HIV-positive subjects were studied during repeat evaluations of clinical improvement or deterioration or as part of randomized clinical trials of gastrostomy feeding, transdermal testosterone, oral oxandrolone or subcutaneous growth hormone.

Dependent Variables

Body weight and height
Total body potassium measured using a four-pi-whole body counter over nine minutes
Bioimpedance analysis was performed using an RJL 101A analyzer.

Independent Variables

HIV infection.

Description of Actual Data Sample:

Initial N: 87 HIV-positive subjects (83 men, 4 women), 62 controls (29 men, 33 women)
Attrition (final N): As above
Age: Mean age cases, 40±8 years; mean age controls, 55±23 years.

Ethnicity

Cases: 46 Caucasian, 23 African-American, 18 Hispanic
Controls: 29 Caucasian, 13 African-American, 8 Hispanic, 12 Asian.

Anthropometrics

Compared to controls, HIV-infected subjects were about 15 years younger and about 10cm taller and had similar body weights and about 10% more body cell mass. The differences between groups were due in part to the much greater proportion of women in the control group.

Location

New York, New York.

Summary of Results:

Variables	R	SEE	Error Mean	Error Median	Absolute Error Mean	Absolute Error Median
Initial prediction	0.771	2.32	0.10	0.10	1.1	1.0
Final prediction	0.891	2.03	0.028	0.00	1.0	0.9
Predicted change in body cell mass	0.755	2.18	0.043	0.00	1.6	1.2

Other Findings

Body weight changed by -0.8±5.6kg (range -19.2 to 14.8kg) between studies in the HIV-infected group, whereas body cell mass by total body potassium changed by 0.3±3.3kg (range -8.8 to 10.8kg).

Body weight changed by 0.1±0.9kg (range -4.0 to 1.6kg) between studies in controls, whereas body cell mass changed by 0.2±1.5kg (range -5.2 to 6.6kg).

Body cell mass change by total body potassium and bioimpedance analysis correlated closely (R=0.755).

After accounting for errors related to repeat measures of total body potassium, the correlation coefficient was 0.784, with a standard error of the estimate of 1.24kg.

The differences between predicted and measured body cell mass change were consistent with a normal distribution.

However, there was a systematic error in prediction, with bioimpedance analysis underpredicting the magnitudes of both gains and losses in body cell mass by total body potassium.

Author Conclusion:

Bioimpedance analysis is a useful surrogate for measuring changes in body cell mass in clinical circumstances. Because total body potassium assesses only intracellular potassium, whereas bioimpedance analysis reflects all intracellular cations, the underprediction of body cell mass change by bioimpedance analysis compared with total body potassium could be related to changes in intracellular potassium concentration as a result of malnutrition or its treatment. The results of these studies clearly demonstrate the ability of bioimpedance analysis to track changes in body cell mass, a tissue compartment otherwise difficult to study in a clinical setting, although the prediction of change in total body potassium by bioimpedance analysis was not statistically better than a prediction based upon weight change. Changes of greater than 1.2kg or about 4% of baseline are likely to represent a real change in body cell mass.

Funding Source:

Government:

NIH Grants DK 42618 and DK 37352

Reviewer Comments:

Cases and controls not similar in terms of age and gender. Baseline differences between groups not statistically analyzed.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	N/A
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	N/A

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		???
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	???
	2.2.	Were criteria applied equally to all study groups?	???
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	Yes
3.	Were study groups comparable?		No
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	No
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	No
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	No
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	Yes
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	Yes
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	Yes
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	N/A
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	N/A
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes