H/A: Body Composition Measurement (2009)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:

To derive predictive equations for estimating body cell mass, fat-free mass and total body water by using single-frequency bioelectrical impedance analysis.

Inclusion Criteria:
  • HIV infection was confirmed by enzyme-linked immunoadsorbent assay testing with protein immunoblot confirmation, or by comparison with the standard case definition for AIDS
  • Studies of HIV serostatus were not performed in the control group.
Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

Three separate data sets were used for these studies.

Design

Case-control study. Cross-sectional analysis was performed with the results of studies in 332 subjects, both HIV-infected and normal controls. 

Statistical Analysis

Comparisons among series and parallel-transformed values of resistance and reactance, exponential versus height2 over R predictive models, and sex-specific versus general predictive equations in predicting body cell mass, fat-free mass and total body water were performed with the POWCOR13 program.

Data Collection Summary:

Timing of Measurements

Predictive equations were derived from direct measurements: Body cell mass by determination of total body potassium (TBK), fat-free mass and fat content by dual-energy X-ray absorptiometry and total body water by 3H20 dilution.

Dependent Variables

  • Body weight and height
  • Total body potassium measured in a four-pi whole-body liquid scintillation counter
  • Body fat content determined through use of dual-energy X-ray absorptiometry
  • Total body water by 3H20 dilution
  • Single frequency bioelectrical impedance analysis.

Independent Variables

HIV infection.

 

Description of Actual Data Sample:
  • Initial N: 332 subjects (206 men and 126 women); 134 were HIV-infected and 198 were normal controls
  • Attrition (final N): As above
  • Age: Mean age of study group was 40 years.

Ethnicity

  • Caucasian subjects: 60 HIV-positve males, 60 HIV-negative males, seven HIV-positive females, 22 HIV-negative females
  • Black subjects: 21 HIV-positive males, 25 HIV-negative males, 12 HIV-positive females, 62 HIV-negative females 
  • Hispanic subjects: 24 HIV-positive males, 16 HIV-negative males, 10 HIV-positive females, 13 HIV-negative females. 

Anthropometrics

Ages were similar in HIV-infected and control subgroups.

Location

New York, NY.

 

Summary of Results:

 Ability of Bioelectrical Impedance Analysis to Predict Change in Total Body Potassium and Fat-free Mass

Variables

Total Body Potassium

Fat-free Mass

All Subjects

76% 82%
Changes greater than 1% 79% 85%
Changes greater than 2% 83% 89%
Changes greater than 3% 83% 95%
Changes greater than 4% 89% 98%

Changes greater than 5%

89%

100%

Other Findings

The measured values of weight, body cell mass (as total body potassium), body cell mass normalized by height and fat-free mass were lower in control women than in control men, whereas body fat content was higher in women than in men.

The HIV subgroups had lower values for weight, body cell mass, total body water, fat and fat-free mass than did race and sex-matched control subjects.

Compared with sex, race had a less important influence on body composition.

Preliminary studies showed more accurate predictions of body cell mass when parallel-transformed values of reactance were used rather than the values reported by the bioelectrical impedance analyzer.

Modeling equations derived after logarithmic transformation of height, reactance and impedance were more accurate predictors than equations using height2 over resistance, and the use of sex-specific equations further improved accuracy.

The effect of adding weight to the modeling equation was less important than the bioelectrical impedance analysis measurements.

The resulting equations were validated internally, and race and disease (HIV infection) were shown not to affect the predictions.

The equation for fat-free mass was validated externally against results derived from hydrodensitometry in 440 healthy individuals; The SEE was less than 5%. 

Author Conclusion:

These results indicate that body cell mass, fat-free mass, and total body water can be accurately estimated with bioelectrical impedance analysis. Body composition can be estimated with simple and easily applied techniques, and that the estimates are sufficiently precise for use in clinical investigation and practice. Further validation of the technique in other clinical situations as well as confirmation of its ability to accurately detect changes in body composition are needed to determine the full applicability of bioelectrical impedance analysis in nutritional evaluation and in monitoring of nutritional support.

Funding Source:
Government: NIH Grants AI 21414, DK 42618, DK 37352
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Differences between cases and controls not evaluated for statistical significance. Groups were not similar in terms of age and gender.

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? ???
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.) ???
  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.) ???
  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? N/A
  7.6. Were other factors accounted for (measured) that could affect outcomes? N/A
  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? N/A
  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)? Yes
  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