CKD: Measuring Body Composition (2009)

Citation:

Avesani CM, Draibe SA, Kamimura MA, Cendoroglo M, Pedrosa A, Castro ML, Cuppari L.A. Assessment of body composition by dua energy X-ray absorptiometry, skinfold thickness and creatinine kinetics in chronic kidney disease patients. Neprhol Dial Transplant. 2004; 19: 2289-2295.

PubMed ID: 15252158
 
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 evaluate the agreement of skinfold thickness (SKF), creatinine kinetics (CK) with dual X-ray absorptiometry (DXA) for measuring body fat and fat-free mass in non-dialyzed patients with chronic kidney disease (CKD).

Inclusion Criteria:
  • Patients with CKD in pre-dialysis
  • Patients older than 18 years of age
  • Clinically stable
  • Mild to advanced CKD with no oedema.
Exclusion Criteria:

Not mentioned.

Description of Study Protocol:

Recruitment

Patients were recruited from an outpatient clinic in the university.

Design

Cross-sectional study.

Blinding used

Blinding of the investigators to different test results was not described.

Intervention

Not applicable.

Statistical Analysis

  • Analysis of variance was used for comparisons of the mean values of body fat and fat-free mass assessed by three techniques
  • Intra-class correlation coefficient (r) was used to test the reproducibility of body fat and fat-free mass measured by SKF and CK and compared with DXA. Values of (r) less than 0.4 indicated reproducibility, between 0.4 and 0.75, medium reproducibility, and values more than 0.75, good reproducibility.
  • Bland and Altman plot analysis was used to assess the agreement between the two methods. The 95% limits of individual agreement between the two methods were calculated as the mean difference between two methods ±2.0 standard deviations
  • The results were expressed as mean±standard deviation. 
Data Collection Summary:

Timing of Measurements

One-time measurements.

Dependent Variables

  • Weight (kg)
  • Body fat (%)
  • Fat-free mass (kg)
  • Serum creatinine (mg/dL).

Independent Variables

  • DXA: using Lunar DPX Bone Densitometer scanner (Kunar Radiation Corporation, Madison, WI)
  • Creatinine Kinetics (kg) by DXA: the CK method calculated fat-free mass according to the formula of Keshaviah et al. Percentage of body fat was obtained subtracting percent of fat-free mass from 100.
  • Skinfold thikness: using a single observer at four sites (triceps, biceps, subscapular and sprailiac). Three sets of measurements were averaged for each site. Body denstiy was calculated according to the formula of Durnin and Womersley and percentage of body fat was derived using Siris' equation. Fat-free mass in kilograms was calculated subtracting body fat from total body weight. 

Control Variables

  • Sex
  • Body mass index (BMI)
  • Diuretic medications
  • Hydration status.
Description of Actual Data Sample:

Initial N: 50 (male, n=38; female, n=12).

Attrition (final N): 50 (male, n=38; female, n=12).

Age: mean age=57 years.

Ethnicity: Not reported.

Other relevant demographics: All patients were in Stage 3 CKD according to the National Kidney Foundation (NKF) classification. The causes of CKD were: diabetes mellitus (40%); hypertensive nephrosclerosis (40%); other causes (4%); unknown causes (16%). There was a predominance of males (76%). Most of the patients were on diuretics or hypertensive medications, but none of them were taking immunosuppressants or corticosteroids.

Anthropometrics: Eighteen percent of the patients were obese and forty-percent overweight. BMI did not match between sexes. Women had a greater BMI (28.4±4.24) vs. males (25.6±4.1)

Location: Sao Paulo, Brazil.

Summary of Results:

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)
Body fat (SKF vs. DXA)
Pre-dialysis CKD patients
50
5.8* %
-2.0
13.6
3.9
Body fat (CK vs. DXA)
Pre-dialysis
CKD
patients
50
8.8*  %       
-8.8
26.4
8.8
Lean body mass (SKF vs. DXA)
Pre-dialysis CKD patients
50
-3.1* kg
-9.9
3.7
3.4
Lean body mass (CK vs. DXA)
Pre-dialysis
CKD
patients
50
-5.5* kg
-18.2
7.3
6.4

*P<0.05, compared to zero bias between tests.

Other Findings

Intra-class coefficients of correlation

Methods

Body fat(%)

 r            95% CI

Fat-free mass (kg)

r                    95% CI

SKF vs. DXA 0.74       0.61-0.8  0.85              0.78-0.93
CK vs. DXA 0.47        0.25-0.69 0.57               0.39-0.76

The percentage of body fat of the patients obtained by either SKF (30.3±8.7) or CK (34.4±12.3) was significantly higher when compared with DXA (24.7±9.6); P<0.05. However, fat-free mass measured by SKF (48.5±7.9) or CK (45.2±7.9) was significantly lower than that obtained by DXA (51.7±8.8); P<0.05. Only females had no difference in fat-free measurements by SKF (38.5±4.2) and DXA (40.9±5.5). 

Author Conclusion:

Skinfold thickness seems to be the method of choice for evaluating body fat. The limitations inherent to DXA in evaluating fat-free mass makes it difficult to designate an alternate method of choice for assessing this body compartment.

Funding Source:
Government: Fundacao de Amparao a Pesquisa do Estado de Sao Paulo (Fapesp)
Not-for-profit
Oswaldo Ramos Foundation
Other non-profit:
Reviewer Comments:

DXA may not be a reliable marker for fat-free mass in patients with CKD because it is influenced by patient hydration. Therefore, it limits its use as a reference method for fat-free mass.

Reproducibility of the study was based on intra-class coefficient of correlation, which is not a good tool to validate different methods.

Bland and Altman plot analysis was used to compare skinfold, creatinine kinetics and DXA methods in measuring body fat and fat-free mass. Mean differences and 95% limits of agreement between SKF and DXA, CK and DXA was used to assess the agreement of the methods. The limits of agreement between SKF and DXA were still wide, which compromises the validation of SKF as a method of choice.   

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? ???
  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? No
3. Were study groups comparable? N/A
  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.) 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.) N/A
  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? ???
  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? ???
  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? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  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? N/A
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? No
  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? No
  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? No
  7.7. Were the measurements conducted consistently across groups? N/A
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? No
  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)? N/A
  8.6. Was clinical significance as well as statistical significance reported? No
  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? 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