CKD: Measuring Body Composition (2009)

Citation:

Barreto Silva MI, Avesani CM, Vale B, Lemos C, Bregman R. Agreement between anthropometry and bioelectrical impedance for measuring body fat in nonobese and obese nondialyzed chronic kidney disease patients. J Ren Nutr. 2008; 18(4): 355-362.

PubMed ID: 18558300
 
Study Design:
Cross-sectional study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To investigate reproducibility and agreement between anthropometry (ANT) and bioelectrical impedance analysis (BIA) in non-obese and obese clinically stable, non-dialyzed patients with stages 3 and 4 chronic kidney disease (CKD), and to examine the factors influencing the agreement between these two methods.

Inclusion Criteria:
  • Non-dialyzed patients with CKD, clinically stable, who were being followed up for at least six months
  • Older than 18 years of age
  • Glomerular filtration rate between 15mL per minute and 60mL per minute.
Exclusion Criteria:
  • Use of corticosteroids or immunosuppressive therapy
  • Apparent edema.
Description of Study Protocol:

Recruitment

Patients were recruited from an outpatient clinic at the Pedro Ernesto University Hospital between 2003 and 2006.

Design

Cross-sectional study.

Blinding used

Not reported. 

Intervention

Not applicable.

Statistical Analysis

  • Pair-matched T-test
  • Concordance correlation coefficient was used to measure the reproducibility of body fat by ANT and BIA
  • Bland and Altman plot analysis
  • Pearson correlation coefficient was used to test the variables associated with the mean inter-method difference in body fat measurements
  • Multiple regression analysis was used to determine the factors influencing the agreement between the two methods
  • Results were expressed as mean±standard deviation.
Data Collection Summary:

Timing of Measurements

One-time measurements.

Dependent Variable

Body fat (BF).

Independent Variables

Measurements of body fat: 

  • ANT: Anthropometric measurements included body weight, height, abdominal circumference and skinfold thickness. Because skinfold thickness cannot be accurately measured in overweight/obese patients, BF was assessed according to the validated equations of Weltman et al. In non-obese patients, BF was assessed by the validated equations of Jackson and Pollock and Jackson et al. The sum of three skinfold thickness measurements was used to calculate BF using the equation of Siri.
  • BIA: Single frequency BIA, Model 310 generator and body, Biodynamics, Seattle, WA.

Control Variables

  • Body mass Index (BMI)
  • Age
  • Sex
  • Total body water.
Description of Actual Data Sample:

Initial N: 105 (61 male; 44 female)

Attrition (final N):105 (61 male;44 female)

Age: Mean age, 64 years

Ethnicity: Not reported

Other relevant demographics: The main causes of CKD were hypertension (n=39), diabetes mellitus (n=17), other causes of CKD (n=24) and unknown causes (n=25). The estimated GFR indicated CKD stages 3 and 4. Patients were well-nourished according to their albumin concentration (4.21mg per dL).

Anthropometrics: The mean BMI of all patients was 26; therefore, sample population was overweight. BMI, body weight and waist circumference were higher in the overweight/obese patients compared with the non-obese group.

Location: Rio de Janeiro, Brazil.

Summary of Results:

Bland and Altman plot analysis between anthropometry (ANT) and bioelectrical impedance (BIA) according to sex and BMI

Test comparisons
Population
N pair
Bland-Altman Limit of Agreement (LOA) Analysis
Mean bias
Lower LOA (lower CI)
Upper LOA (upper CI)
Standard Deviation (SD)
BF by ANT and BIA
Male, non-obese
pre-dialysis
CKD patients
26
-0.9
-6.8
4.9
    
BF by ANT and BIA
Female, non-obese
pre-dialysis
CKD patients
22
0.4
-3.4
 
4.3
 
BF by ANT and BIA
Male, obese
pre-dialysis
CKD patients
35
5.7
-3.2
 
14.7
 
FM by ANT and BIA
Female, obese
pre-dialysis
CKD patients
22
6.4
 
-1.8
14.7
 

 

Predictors of agreement between ANT and BIA in the assessment of body fat (adjusted R2=0.42)

Independent variables Coefficient Standard error

t

P
Constant -17.51      
Age (y) -0.06 0.029 -2.04 0.0436
Sex 3.45 1.070 3.22 0.0017
BMI 0.31 0.095 3.26 0.0015
Total body water (L) 0.30 0.068 4.460 <0.0001

 

Other Findings

  • In the overweight/obese group, ANT was significantly higher than that obtained by BIA (28.9±6.0 vs. 22.9±6.3) when body fat was assessed by ANT and BIA according to BMI
  • In the non-obese group, there was a strong concordance correlation coefficient between both methods (r=0.78), and this correlation was stronger between females than males (r=0.88 and r=0.67)
  • There was a positive and strong association between the mean inter-method difference and mean BF (ANT+BIA/2), r=0.50; P<0.001 and BMI, r=0.54; P<0.001, as well as age (r=-0.22; P<0.001) and total body water (0.42; P<0.001).
Author Conclusion:

For non-obese patients, ANT and BIA can be applied equally well for assessing body fat. For overweight/obese patients, a weak agreement was observed. BMI, sex, body water and age were the factors influencing the agreement between ANT and BIA.

Funding Source:
Other: Not reported
Reviewer Comments:

The mean inter-method differences between ANT and BIA in measuring body fat showed a great difference between the limits of agreement in male non-obese CKD patients (-6.8kg; 5kg), although the authors claimed a good agreement using the two approaches. However, in non-obese females the limit of agreement was good.

Population stratification by BMI can bring bias to the overweight/obese group because they were pulled together.

BIA is not adequate to measure BF in CKD patients because it does not consider the degree of hydration status and bone mineral content, and thus is likely to affect the validity of this technique in CKD patients, especially with the obese group.

An important limitation was the lack of a gold-standard method such as DXA to compare with the other two methods.

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) Yes
  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? Yes
  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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  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) N/A
  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.) N/A
  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")? No
4. Was method of handling withdrawals described? ???
  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? ???
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? ???
  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? N/A
  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? ???
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? No
  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? ???
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? ???
10. Is bias due to study's funding or sponsorship unlikely? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? ???