CKD: Measuring Body Composition (2009)

Citation:

Woodrow G, Oldroyd B, Smith MA, Turney JH. Measurement of body composition in chronic renal failure: Comparison of skinfold anthropometrhy and bioelectrical impedance with dual energy X-ray absorptiometry. Eur J Clin Nutr. 1996; 50: 295-301.

PubMed ID: 8735310
 
Study Design:
Case-control study.
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To compare measurement of total body fat percentage (%TBF) and free fat mass (FFM) by skinfold anthropometry (SFA) and bioelectrical impedance (BIA) using dual energy X-ray absorptiometry (DEXA) as a criterion method in patients with CKD.

Inclusion Criteria:
  • CKD patients on conservative treatment or under dialysis (hemodialysis and CAPD)
  • Clinical criteria to be close to a normal state of hydration with no significant edema
  • Control subjects with similar BMI, age and height to the CKD patients
  • Caucasian population.
Exclusion Criteria:

Not meeting the inclusion criteria.

Description of Study Protocol:

Design

Case-control study. 

Statistical Analysis 

  • Bland & Altman: Limits of agreement between the different methods were defined as the mean difference between methods, 1.96+SD
  • Pearson correlation coefficient calculated the correlation of the inter-method difference and mean values 
  •  Unpaired two-tailed T-test
  • One-way analysis of variance to perform the comparison of %TBF and FFM by the three different methods for the CKD and control groups.

 

Data Collection Summary:
  • Timing of measurements: One-time measurements
  • Dependent variables: Body composition (%TBF, FFM). 

Independent Variables

Measurement of body composition:

  • Dual energy, X-ray absorptiometry (DEXA) was performed using Lunar DPX-L scanner
  • Bioelectrical impedance (BIA) was performed using a RJL 101A system and the Holtain system for comparison with the former one to determine the comparability of different systems and prediction equations
  • Skinfold anthropmetry (SFA) was measured by a single observer using four sites (biceps, triceps, subscapular and suprailiac). Each site was measured in triplicate. Body density was calculated using the formula of Durnin and Womersley. %TBF was derived from body weight minus body fat mass.  

Control Variables

  • BMI
  • Age
  • Height.

 

Description of Actual Data Sample:

Initial N

  • 69 (36 males, 33 females)
  • Conservative treatment: 23
  • Controls: 27 (13 males, 14 females)
  • Hemodialysis: 22
  • Peritoneal dialysis: 24.

Attrition (final N)

  • 69 (36 males, 33 females)
  • Conservative treatment: 23
  • Controls: 27 (13 males, 14 females)
  • Hemodialysis: 22
  • Peritoneal dialysis: 24.

Age

Mean age of all CKD was 58 years old.

Ethnicity

Caucasian.

Other Relevant Demographics

CKD patients under conservative treatment had advanced renal disease with serum creatinine greater than 500umol per L. Only Caucasian patients were studied, to avoid an additional source of variation in measurements.

Anthropometrics

BMI and weight were well matched with controls at baseline. Subjects were not overweight or obese.

Location

Leeds, UK.

 

Summary of Results:

Mean Bias ± 1.96 SD (Limits of Agreement) for Inter-method Comparisons for %TBF Expressed as Percentage of the Mean Values for Pre-dialysis CKD Patients

Test Comparisons

Population

N Pair

Bland-Altman Limit of Agreement (LOA) Analysis

Mean Bias

Standard Deviation (SD)

%TBF by DEXA and BIA

CKD pre-dialysis patients

23

-11.9%
 

54.2

%TBF by DEXA and SFA

CKD pre-dialysis patients

23

-5.8%

52.1

%TBF by DEXA and BIA

Peritoneal dialysis

24

-14%

36.2

%TBF by DEXA and SFA

Peritoneal dialysis

24

-9.6%

40.2

%TBF by DEXA and BIA

Hemodialysis

22

-5.2%
 

37.0

%TBF by DEXA and SFA

Hemodialysis

22

-4.6%

35.6

%TBF by DEXA and BIA

Control

27

-8.6%
 

25.5

%TBF by DEXA and SFA

Control

27

13.1%
 

31.2

 

Mean Bias ± 1.96 SD (Limits of Agreement) for Inter-method Comparisons for FFM Expressed as Percentage of the Mean Values for Pre-dialysis CKD Patients

Test comparisons

Population

N pair

Bland-Altman Limit of Agreement (LOA) Analysis

 

Mean bias

Standard Deviation (SD)

 

FFM by DEXA and BIA

CKD pre-dialysis patients

23

4.4 %

17.8

 

FFM  by DEXA and SFA

CKD pre-dialysis patients

23

2.7 %

16.7

 

FFM  by DEXA and BIA

Peritoneal dialysis

24

6.8 %

14.9

 

FFM  by DEXA and SFA

Peritoneal dialysis

24

5.9 %

 15.8

 

FFM by DEXA and BIA

Hemodialysis

22

2.9 %

12.4

 

 

FFM by DEXA and SFA

Hemodialysis

22

2.5 %

13.5

 

FFM by DEXA and BIA

Control

27

3.4 %

8.3

 

FFM by DEXA and SFA

Control

27

-4.2 %

12

 

 

 

 

 

 

 

 

Author Conclusion:

In CKD, errors of both BIA and SFA in comparison with DEXA were greater than in normal subjects.The magnitude of the limits of inter-method difference were relatively much greater for measurement of percentage of total body fat than free fat mass for both BIA and SFA in CKD patients and control subjects.

Funding Source:
University/Hospital: University of Leeds and United Leeds teaching hospitals special trustees
Reviewer Comments:
  • 67% of the population were on dialysis treatment.Therefore, most of the results, not shown here, were related to all CKD patients rather than their subgroups (non-dialyzed vs. dialyzed).
  • Mean bias for inter-method comparison for percentage of total body mass and free fat mass showed that the inter-method differences were proportionally larger for the non-dialyzed CKD group compared with the dialyzed groups. However, this difference was much less marked for FFM than for the measurement of %TBF. 
  • Hydration likely plays a role due to probable deviation of body composition in CKD patients from that of normal subjects upon which the predictive formulas are based.
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? ???
  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? 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? ???
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? 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.) 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? 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? ???
  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.) ???
  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? 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? No
  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? No
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  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? ???
  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? ???
  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? No
  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)? ???
  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? No
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
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