SCI: Preventing Overweight (2007)

Citation:

Buchholz AC, McGillivray CF, Pencharz PB. The use of bioelectric impedance analysis to measure fluid compartments in subjects with chronic paraplegia.  Arch Phys Med Rehabil 2003;84:854-861. 

PubMed ID: 12808538
 
Study Design:
Case-control
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

1. To determine the sensitivity and specificity of BMI as a surrogate measure of obesity in men and women with chronic paraplegia

2. To validate bioelectric impedance analysis (BIA) as a method of measuring body composition in the same group

Inclusion Criteria:

Healthy subjects with paraplegia; none described for control subjects

Exclusion Criteria:
None given; however, all subjects were euthyroid
Description of Study Protocol:

Recruitment

Flyers and pamphlets (Toronto Rehabilitation Institute, Ontario Wheelchair Sports Association, Ontario March of Dimes, Canadian Paraplegic Association, Spina Bifida and Hydrocephalus Association of Toronto for paraplegic subjects; University of Toronto, Ryerson University, and staff of The Hospital for Sick Children for control subjects)

Design

Evaluation, in paraplegic and control subjects, of two diagnostic procedures (BMI and BIA) that measure components of obesity. Subjects were group matched on the basis of BMI.

Blinding used (if applicable):  Not applicable

Intervention (if applicable):  Not applicable

Statistical Analysis

  • chi-square test (to determine differences in sex distribution between the 2 study groups)
  • student t tests (to determine differences between the 2 study groups
  • 2-way ANOVA for unbalanced designs (to determine if there was a significant group by sex interaction for % FM)
  • Sensitivity of BMI (# true positive/[# true positive+# false negative])x100%
  • Specificity of BMI (# true negative/[# false positive+ # true negative])x100%)
  • ROC (receiver operator characteristic)curve (to determine a more relevant BMI cutoff)
  • Pearson correlation coefficient (to quantify the univariate association between TBW or ECW and selected predictor variables)
  • multivariate technique of all possible regressions (further evaluate the associations between TBW/ECW and selected predictor variables)
  • Mallow's Cp statistic (further evaluate the associations between TBW/ECW and selected predictor variables)
  • Bland and Altman analyses (to determine bias between predicted and measured TBW/ECW)
  • paired t tests (to determine significant differences between predicted and measured TBW/ECW)

 

Data Collection Summary:

Timing of Measurements

One time only

Dependent Variables

  • Total-body water (TBW) by deuterium dilution
  • Extracellular water (ECW) by corrected bromide space
  • Fat-free mass (FFM) calculated ( TBW/0.732
  • Fat mass (FM) calculated (weight minus FFM)
  • Single-frequency (50 kHz) whole-body and segmental BIA (model 101, RJL Systems, MI)
  • Multifrequency whole-body BIA (Xitron Technologies Corp, CA)

Independent Variables

  •  paraplegic lesion (complete/incomplete)

Control Variables

  • none

 

Description of Actual Data Sample:

Initial N: 19 men and 12 women with paraplegia; 62 able-bodied control subjects (30 men, 32 women)

Attrition (final N): no attrition

Age: Paraplegia mean, 34.2±8.8 years; control mean, 28.6±7.2 years.

Ethnicity: not reported

Other relevant demographics: None mentioned

Anthropometrics: see results table

Location: The Hospital for Sick Children, Toronto, Canada

 

Summary of Results:

 Body Composition and BIA Parameters

Variables

Paraplegia group (n=31)              

mean±sd

Control group      (n=62)

mean±sd

p value, difference between groups

Height/length (cm)

162±14.6

170±10.3

p=0.0160

Weight (kg)

 64.3±16.2

 66.6±11.2

 NS

BMI (kg/m2)

 24.6±6.4

 22.9±2.0

 NS

TBW (L) 32.2±8.0 37.3±7.9 p=0.0024
TBW (% body wt) 50.6±6.8 55.6±5.1 p=0.0001
FFM (kg) 44.0±11.0 51.0±10.8 p=0.0024
FFM (% body wt) 69.2±9.2 76.0±7.0 p=0.0001
FM (kg) 20.2±9.0 15.8±4.8 p=0.0142
FM (% body wt) 30.8±9.2 24.0±7.0 p=0.0001

ECW (L)

15.1±4.0 14.4±3.1 NS
ECW (% body wt) 23.8±4.3 21.4±2.6 p=0.0069

Other Findings

There were no differences in body composition between the subgroup of individuals with paraplegia and incomplete lesions vs complete lesions

Multifrequency BIA offered no greater prediction of TBW or ECW than single-frequency BIA; high-frequency BIA offers no greater prediction than BIA at 50 kHz in the group with paraplegia.

BMI has excellent specificity (100%) but poor sensitivity (20%) in distinguishing obese from nonobese individuals with paraplegia.

Author Conclusion:

The BMI specificity and sensitivity findings suggest that a) individuals with paraplegia and a BMI >/= 30 kg/m2 are likely truely obese; b) no conclusions about body fatness can be made for those with a BMI < 30 kg/m2.  Moving the obesity cutoff to >/= 25 kg/m2 improved sensitivity (to 60%) without compromising specificity (preliminary data and should be used with caution).

TBW (and therefore FFM and FM) and ECW can be reasonably well predicted by using single-frequency BIA and the following equations:

  • ECW (in L) = -0.025+1.03sex+0.187wt+0.0041(ht2/Xc)-0.033 sexXwt
  • TBW (in L) = 2.11-0.1age+3.45sex+0.34wt+0.28(ht2/R)-0.086sexXwt

where L is liter, wt is kg, ht is cm, and Xc and R are whole-body BIA results.

 

Funding Source:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Strengths of this study include the detailed description of methodology and statistics, and the inclusion of women.

While this is essentially a cross-sectional study with a convenience sample and while the results are preliminary and should be used with caution,  the detailed analysis of results provides useful information for this subpopulation of individuals with SCI.


Ethnicity of subjects, and duration of disease for SCI not reported

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) ???
  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) Yes
 
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? No
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  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? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  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.) N/A
  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? Yes
  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? Yes
  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? Yes
  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? Yes
  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