Anthropometric assessment of nutritional status in renal disease

RESEARCH

BRIEFS

Phase Angle Predicts Survival in Hemodialysis Patients Glenn M. Chertow, MD, MPH, *, J- Dunny 0. Jacobs, MD, MPH, f /. Michael Lazams, MD, f Nancy L. Lew, SM, f and Edmund G. Lowvie, MDf

Objective: To determine the relation between phase angle by bioeiectrical impedance analysis (BIA) and survival in hemodialysis patients. Design: Cohort analytic study. Setting: One hundred one free-standing outpatient dialysis units. Patients: Three thousand nine adult patients on thrice weekly hemodialysis. Patients with amputations above the transmetatarsal site were excluded from participation. Main Outcome Measure: Vital status, with follow-up to at least 1 year. Results: Mean phase angle was 4.8 ? 1.8 degrees. Patients with narrow (low) phase angle experienced an increased relative risk (RR) of death (<3 degrees; RR 4.3; 95% confidence interval [Cl], 2.9-6.2; and 3 to 4 degrees); RR 2.2; 95% Cl, 1.6-3.2; compared with the 26 degrees reference). There were no significant differences in risk among patients with phase angle 4 to 5 degrees (RR 1.2; 95% Cl, 0.8-l .8), 5 to 6 degrees (RR 1 .l; 95% Cl, 0.7-l .7), and 26 degrees, suggesting a nonlinear relation between phase angle and survival. The RRs for phase angle <4 degrees remained statistically significant after adjusting for age, gender, race, serum albumin and creatinine concentrations, and dialysis intensity (~3 degrees, RR 2.2; 95% Cl, 1.6-3.1, and 3 to 4 degrees, RR 1.3; 95% Cl, 1.0-l .7, compared with all patients 24 degrees). Conclusions: In patients on hemodialysis, BIA-derived phase angle <4 degrees was associated with an increased RR of death, even after adjustment for case mix and several nutritional indicators. Further research is required to determine whether BIA can be used to monitor health status over time, or to gauge response to nutrition support or other clinical interventions in patients with end-stage renal disease. o 1997 by the National Kidney Foundation, Inc.

P

ROTEIN ENERGY malnutrition afflicts a large fraction of hemodialysis (HD) patients,‘.” and it is an important determinant of mortality and morbidity.4-x Several methods of nutritional assessment have been applied in this population, including estimates of dietary intake, anthropometry, and biochemical tests, including

204

serum concentrations of creatinine, albumin, and prealbumin. These biochemical indicators have been shown repeatedly to predict survival in HD patients, although their levels can be confounded by other disease processes (eg, liver disease, inflammation, overhydration), and they do not capture the entire dimension of malnutrition. Body conposition analysis has attracted some interest; however, most diagnostic methods are too costly and/or cumbersome to be applied in clinical practice. Bioelectrical impedance analysis (BIA) has been explored as a method of body composition analysis for more than a decade,” and it has recently been applied to the dialysis population by several groups of investigators. lo-l5 Briefly, bioelectrical impedance (Z) is the vector sum of resistance (R) and reactance (Xc). Resistance is the opposition

ANTHROPOAfETRIC

ASSESSME&-T

body cell mass is the location of the body’s metabolic processes.’At the tissue-systemlevel, the body consistsof adipose,muscle, and skeletal tissues.Adipose tissue is located in subcutaneous and visceral compartments, and its distribution on the body is under hormonal and genetic control. Skeletal muscle is the largest tissuecomponent of the body accounting for about half the body weight in a healthy adult. Skeletal muscle consists of muscle tissue, nerves, tendons, and interstitial adiposetissue.The skeleton is the major reservoir of body minerals. Thus, body weight is the sumof the weights of adiposetissue,skeletal muscle, the skeleton and a residual of visceral organs nerves, blood vesselsand extracellular water. The intracellular water is included in the various tissuesof the body. There are direct and indirect methods of measuring body composition. Direct methods measure specific chemical or anatomical constituents that are then used to calculate components of body composition. Direct methods tend to be accurate, but they can be invasive. Indirect methods are frequently noninvasive but provide less accurate measuresof body components that are used to predict body composition. Indirect estimatesof body composition use measuresof body weight and volume, bioelectrical impedance, body size, and subcutaneousadiposetissuem statistical models. These models are basedon assumptions regarding the density of body tissues,the concentrations of water and electrolytes in FFM and biological inter-relationships among normal individuals. To be valid, indirect methods must be compared with resultsfrom direct methods. Indirect methods have larger errors for body composition estimatesthan direct methods.

Table 1. Anthropometric

Measurements

Measurement

in MDRD

in Assessing

or HEM0

Total body size Total body size Adipose tissue Adipose tissue Fat-free mass and adipose Adrpose tissue Fat-free mass Lower leg length Body size studies.

177

STA’TW

Anthropometry Some body measurementscommonly usedin a nutrition assessment are listed in Table 1. Those measurementsmarked with an asteriskwere collected in the Modification of Diet m Renal Disease(MDRD) Project and the current Hemodialysis(HEMO) study (Morbidity and Mortality in Hemodialysis Patients), two large multicenter studies of renal disease.sz”Stature and weight provide a general description of body size and mass.Body weight is a rough measure of total body energy stores. The triceps and subscapular skinfolds measure subcutaneousfat thickness on the limbs and trunk, and abdominal circumference is an index of internal adiposetissue.*” Calf circumference 1san indirect measure of muscle mass.“,12Elbow breadth is a useful measuresof frame size, and knee height can be used to estimatestature.i3-‘j Body measurementscan also be combined m indices that describe levels of body composition, nutritional status, or risk for disease.‘6-‘8Stature and weight are used in the body mass index or BMI (weight/stature2 in kg/m’) to describe levels of body composition. Levels of BMI lessthan 19 and greater than 28 are associatedwith increased morbidity and mortality.‘” Midarm circumference and triceps skinfold are combined to calculate midarm muscle area. Midarm muscle area and calf circumference are related to levels of protein stores or used as a marker for FFM. Anthropometric data are also used as covanates to help account for additional variance m statisticalmethods for estimating body composition.20 The use of standardized anthropometric techniques is important, especially if parameters of a nutrition assessment are compared with reference data or with data from related studies. There are

Nutrttional

Assessment

Stature* Weight* Triceps skrnfold* Subscapular skinfold* Arm circumference* Abdominal circumference Calf circumference* Knee height* Elbow breadth* *Measured

Used

OF ,WlTRITIOAAL

tissue

Status Accuracv

Rekabilitv

Very high Very high Moderate Moderate Hrgh Moderate Hrgh High High

Very high Very high Very high Moderate Moderate Moderate Moderate Hrgh Moderate

Utrlitv High High Moderate Moderate Moderate Moderate High Moderate

178

WILLIAM

CAMERON

several texts that contain written techniques for the measurements listed in Table 1.21,” These methods are the same or similar to those used by the National Center for Health Statistics to collect corresponding measurements in the Third National Health and Nutrition Examination Survey (NHANES III). The anthropometric methods used in NHANES III were chosen to monitor the health and nutritional status of infants, children, adults, and the elderly. A video tape documenting the measurement techniques in NHANES III is also available.23

Effects of Renal Disease on Anthropometric Data Renal patients frequently present special problems for anthropometry.71 The assistance of two health technicians for the roles of examiner and recorder are generally required to accommodate the person’s health conditions. The examiner is responsible for positioning the subject and taking each measurement. The recorder’s role is to assist the examiner in taking correct measurements by helping to position the subject and equipment to ensure that accurate data are recorded. Measurements should be taken on the right side of the body because this side is used in all national reference data in the United States. However, if the patient has a vascular access, a cast, an amputation or other limitations on the right side, it may be necessary to take measurements from the left side of the body. Also, placement of the vascular access in different parts of the body in hemodialysis patients will cause continuous shiftmg of body locations for measurements of circumferences and skinfolds. Some persons with renal problems may have difficulty standing or maintaining an erect posture and some are chair- or bed-fast. Recumbent anthropometric techniques are applicable to those renal patients who are unable to stand for measurements. Recumbent measurements are reliable and accurate, and the values are not systematically different from those using corresponding standing techniques.2” Because diabetes is one of the comorbid conditions with renal disease, some sufferers may experience amputations of the limbs due to vascular degeneration. Stature cannot be measured accurately m these and other nonambulatory individuals. The estimation of stature from

CHUMLEA

recumbent knee height with known errors is the best method at present for providing this information for clinical and nutrition assessments.‘” For those persons with bilateral amputations of the lower leg, there is presently no suitable method of estimating stature except for a self-report. Stature prediction equations for persons with bilateral lower leg amputations will be available in the near future using measures of buttocks-knee length. The measurement of weight in renal patients can require special equipment, such as bed or wheelchair scales. Changes in weight parallel hydration status, energy, and protein balance. In adults, usual body weight varies less than +l.O kg/d. A consistent loss in weight of more than 0.25 kg/d over time indicates negative energy or water balance, or a combination of the two. Weight gain or loss, not associated with changes in body water, are associated with different relative rates of change in the subcutaneous and visceral adipose tissue compartments and from different anatomic sites. Measures of change in body weight should include anthropometric indices of body composition at regular but not frequent intervals. These measurements will provide a better understanding of the underlying parameters of a change in weight, such as alterations in the relative amounts and anatomical distributions of adipose and muscle tissues.“s The effect of total body or regional alterations in water content on anthropometric measurements and body composition in patients with renal disease is not well defined. An abnormal hydration status alters the assumptions underlying the methods and the density of the fat-free body and relationships with anthropometry. The level of hydration affects skinfold and circumference measurements, and it is recommended that these be collected from the person after dialysis. Renal disease alters the water-based assumptions for body composition validated m normal individuals. In renal failure patients, edema may affect to a substantial degree estimates of FFM based on an assumed average hydration of 73%. Thus, m this water-retaining disease, the concept of FFM must be reassessed. Edema-free FFM may be a more useful nutrition parameter than FFM.a6 In other patients with chronic renal failure, total body potassium may not correlate closely with total body nitrogen, which is an indicator of total body protein. This indicates that in renal disease total

ANTHROPOMETRIC

ASSESSMENT

body potassiummay not be a suitable estimate of FFM.h

Limitations

and Sources of Error

There are several limitations and sources of error for anthropometry.r’J7 The person being measured and the person taking the measurements are the major contributors to measurement error. If equipment is well-maintained and calibrated, then it provides little to the overall errors. The limits of anthropometry are in their gross nature. Stature and weight usedto calculate BMI provide only an index of body composition. A skinfold only measuresa compressibleamount of subcutaneousadiposetissuethicknessat a specific location. The combination of the variances of the measurementsaffects the specific use of anthropometry. Regardless of the method selected, none are perfect, but frequently, the errors are ignored or forgotten. For an assessment of a renal patient, errors can have clinical relevance asthe person is treated and observed over time.

Effects of Age, Gender, Ethnicity on Anthropometric

and Data

The specific effects of renal diseaseon anthropometnc measuresare further compounded by the normal effects of age, gender, and race of individual patients. Changesin body composition occur throughout the lifespan, and these are associatedwith corresponding changesin various physiologic functions that affect metabolism, nutrient intake, physical activity, and risk of chronic diseases.Throughout childhood, there is an increasein the mineralization of the skeleton with growth and increasesin the density of FFM.” In addition, the changesin the hormonal milieu alter the distribution and proportions of adipose, muscle, and skeletal tissuesin children as they mature into adults. These changes are further affected by the variation among children in the onset and duration of maturation. There is a decreasein the body cell masswith old age resulting from reductions m total body water, but there are conflicting reports regarding corresponding changes with age in extracellular water.‘s Changesin amounts of total body water and the proportion of mtercellular and extracellular fluid volumes affect the relative hydration of FFM.a9

OF A’UTRITIOA’AL

STATVS

179

In addition. loss of bone mmeral with age requires changes in assumptionsregarding the density of fat-free tissues.Bone mineral accounts for asmuch as6% of FFM but decreasessubstantially after menopause.30Levels of FFM and bone mineral also decreaseasphysical activity decrease with hemodialysis. Changes in FFM and calf circumference may be due in part to decreased levels of physical activity. A significant negative correlation between age and calf circumference in elderly men, but not women, may be due to general lossof muscle in responseto the reported greater reduction m physical activity among men than women. Lossesof FFM with age may be due to reduced levels of physical activity reported in the elder1y.j’ Tincepsand subscapularskinfold thicknessesare significantly correlated with total and percent body fat m children and young adults.s2 In middle-aged adultsand the elderly, body measurements, circumferences of the trunk, rather than skinfolds provide more information regarding stores of body fat. l2 With aging, adipose tissue thicknessesdecreaseon the arm and the leg asfat redistributes to the trunk, so that correlations of skinfold thicknesseswith total and percent body fat are low. These changes are associatedwith poor limb and abdominal muscle structure or tone, as well as changesin fat patterning. Postmenopausal women are reported to have more upper-body fat than premenopausal women so that some changesmay have endocrinologic sigmficance. Changes in the elasticity, hydration, and compressibility of subcutaneousadipose and connective tissuesin the elderly can alsoalter the relationship of anthropometry to body composition and the interpretation of indices of adipose tissuedrstnbution. Ethnic differences m body composition are affected by differences m socioeconomic status, diet, use of health care and levels of genetic admixture. African-Americans have more dense bones and tend to have more bone mineral than non-Hispanics.33There are more African-American women than non-Hispanic white women at the extremes of the distributions for body fatness. Data for body composition for large samplesof African, Hispanic, or Asia-Americans are hmited.jGm3”However, reasonably extensive anthropometric data are available for African, Hispanic, and non-Hispanic white Americans from the NHANES survevs.

180

WILLIAM

Anthropometric

Reference

CAMERON

CHUMLEA

Acknowledgment

Data

The NHANES surveys are recognized for then multiple methods of data collection includmg interviews, physical examinations, physiological testing, and biochemical assessments from a representative sample of the United States population.37 Mean values and distribution statistics for stature, weight, and selected body circumferences, breadths and skinfold thicknesses of children and adults are available from the US National Health Surveys. 38-41 Similar reference data for the present US population will be available from NHANES III in late 1997. However, preliminary results from NHANES III, based on percentiles for BMI, indicate that the prevalence of obesity in the US adult population has increased.4’,43 For African-American women, the prevalence of obesity approaches 50% of the adult population. The increased prevalence of obesity in the US population raises serious questions about the use of NHANES III data as a “health” reference guide. Only limited anthropometric reference data for persons with end stage renal disease have been published.4i With the extensive investigation of renal disease such as in the HEM0 and MDRD Studies, current reference data for the body measurements of persons with renal disease will become available in the future.

Summary

The authors thank Dr. Shumei Guo (Wright State Umverstty School of Medrcme), Dr. Johanna Dwyer, Sandra Powers, Jerrllynn Burrowes, Roberta Henry (from the HEM0 Study),

David and

Cockram

(Ross

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