EAL

H/A: Body Composition Measurement (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To compare measurements of fat distribution between two different DXA machines
To determine whether the use of different DXA machines may affect the diagnosis of HIV-associated lipodystrophy.

Inclusion Criteria:

HIV-infected patients confirmed by ELISA and Western Blot assay
Subjects were required to have lipodystrophy or no lipodystrophy.

Exclusion Criteria:

Wasting (defined as weight loss of more than 10% of usual body weight during the past six months)
Concomitant use of diuretics
Systemic corticosteroids
Pregnancy
Breastfeeding.

Description of Study Protocol:

Recruitment

Patients were recruited from the outpatient clinics of the Communicable Disease Centre, Tan Tock Seng Hospital, the national referral center for HIV infection in Singapore.

Design

Cross-sectional study.

Statistical Analysis

Comparisons of the duplicate Lunar and Hologic body composition measurements from individual patients was made by paired T-tests
Trends in inter-machine differences were evaluated using Bland and Altman's method and linear regression analysis
Two-sample T-tests were used to compare means for lipodystrophy and non-lipodystrophy subjects measured by one machine
The DXA contributions to composite scores for lipodystrophy diagnosis were calculated using previously published conversion factors and the mean lipodystrophy scores from the two DXA machines were compared with paired T-tests.

Data Collection Summary:

Timing of Measurements

Body composition was measured on two DXA machines on the same day and compared.

Dependent Variables

Body weight, height, BMI
Body composition measured in two DXA machines: Lunar and Hologic.

Independent Variables

HIV infection
Presence of lipodystrophy: Patients were classified as having lipodystrophy if they had at least one confirmed moderate or severe feature of lipoatrophy, diffuse fat accumulation or lipomatosis that had arisen since the diagnosis of HIV infection.

Control Variables

Medical records were reviewed and clinical information was abstracted including CD4 counts, viral load and antiretroviral treatment history.

Description of Actual Data Sample:

Initial N: 24 HIV-infected patients, 12 of whom had clinically diagnosed lipodystrophy
Attrition (final N): 24 subjects (16 males, eight women)
Age: Mean age subjects with lipodystrophy, 46.3±14.2 years; mean age without lipodystrophy, 35.3±4.7 years.

Other Relevant Demographics

Mean CD4 count in subjects with lipodystrophy, 405±226 cells per ml; without lipodystrophy, 214±143 cells per ml
Mean viral load in subjects with lipodystrophy, 2.21±1.02 log₁₀copies per ml; without lipodystrophy, 2.90±1.54 log₁₀copies per ml.

Location

Singapore.

Summary of Results:

Variables	Hologic	Lunar	Difference	P-value
Total body mass, kg	56.3±7.1	57.4±7.2	-2.1	<0.001
Total body fat, kg	13.0±5.7	11.9±6.0	1.1	<0.001
Total body fat, %	22.9±9.6	20.5±9.9	2.4	<0.001
Total lean tissue, kg	41.4±6.8	43.3±6.8	-1.9	<0.001
Total body mineral content, kg	1.9±0.3	2.3±0.3	-0.4	<0.001
Limb fat, kg	5.8±2.5	4.1±2.3	1.7	<0.001
Limb fat, %	24.6±10.3	16.8±9.4	7.8	<0.001
Trunk fat, kg	6.4±3.4	7.4±3.8	-0.9	<0.001
Trunk fat, %	22.3±11.3	24.7±11.4	-2.5	0.001
Arm fat, kg	1.7±0.7	0.8±0.5	0.9	<0.001
Arm fat, %	27.9±11.6	14.5±8.8	13.4	<0.001
Leg fat, kg	4.1±1.9	3.2±1.9	0.9	<0.001
Leg fat, %	23.4±10.2	17.5±9.6	5.9	<0.001
Trunk-to-limb fat percent ratio	0.89±0.28	1.62±0.47	-0.72	<0.001
Trunk fat % minus limb fat %	-2.3±6.2	7.9±5.3	-10.3	<0.001
Limb lean tissue, kg	16.7±3.1	18.8±3.3	-2.1	<0.001
Trunk lean tissue, kg	21.4±3.7	21.0±3.3	0.4	<0.090
Arm lean tissue, kg	4.2±1.0	4.8±1.0	-0.6	<0.001
Leg lean tissue, kg	12.5±2.2	14.0±2.4	-1.5	<0.001

Other Findings

Subjects with lipodystrophy were significantly older, had a longer duration of HIV infection and a higher CD4 count than those without lipodystrophy. 22 of 24 patients were receiving highly active antiretroviral therapy including a protease inhibitor.

Hologic gave significantly higher values than Lunar DXA for total body fat percent (22.9% vs. 20.5%, P<0.001), arm fat percent (27.9% vs. 14.5%, P<0.001) and leg fat percent (23.4% vs. 17.5%, P<0.001), as well as significantly lower values than Lunar for trunk fat percent (22.3% vs. 24.7%, P<0.001) and trunk-to-limb fat percent ratio (0.89 vs. 1.62, P<0.001).

When measured by Lunar, patients with lipodystrophy had significantly lower leg fat percent (13.5% vs. 21.6%, P=0.04) and higher trunk-to-limb fat percent ratio (1.85 vs. 1.38, P=0.012) than those without lipodystrophy.

When measured by Hologic, patients with lipodystrophy had values of leg fat percent (20.1% vs. 26.8%, P=0.11) and trunk-to-limb fat percent ratio (0.95 vs. 0.85, P=0.43) that did not differ significantly from those without lipodystrophy.

There was a significant difference in the contribution to a composite lipodystrophy score between Lunar and Hologic measurements.

Author Conclusion:

DXA machines from different manufacturers give major differences in measurements of body fat content and distribution, and this may affect the ability to distinguish patients with lipodystrophy from those without lipodystrophy. Further standardization of DXA technology is needed before widespread application in the clinical diagnosis of lipodystrophy.

Funding Source:

Government:

Bio-Medical Research Council of Singapore (BMRC) Grant Number 01/1/28/18/026

Reviewer Comments:

Author notes that the results should be taken as an illustration of the limitations of DXA in general, not as an indictment of one particular manufacturer.

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?		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?		Yes
	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?	Yes
	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?	Yes
	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.)	Yes
	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?	Yes
	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?		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?	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?	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?	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?	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)?	N/A
	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