Understanding the role of lean body mass (LBM) and how to estimate its contribution to the total body mass may be important to understanding mortality risk in hemodialysis (HD) patients.

This information guides the clinician in designing effective interventions to optimize patients’ nutritional status and functional ability. Currently, many HD patients have high body mass index values but are actually low in LBM. Without adequate LBM, patients’ functional status, activities of daily living, and, ultimately, quality of life will be negatively impacted.

Measuring lean body mass

LBM, also called fat free mass, is predominately fluid, protein, and minerals. LBM can be measured a variety of ways that vary in their accuracy, cost, and skill level needed to conduct the measurements. Techniques for measuring LBM range from dual x-ray absorptiometry (DEXA) to near infrared reactance, skinfold measures, and, finally, hand-grip strength. 

DEXA is extremely accurate and considered a gold standard in body composition determination, but it has some draw backs: a DEXA measurement costs approximately $300, the clinician must attend special radiologic training, and the patient must be able to travel to the machine (which is not portable).


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Portable tools

Near infrared, skinfolds, and hand-grip strength are all portable assessment techniques that can be done at the dialysis center and used post-treatment. However, the dialysis center must bear the cost of the equipment. A Lange skinfold caliper is approximately $200 and a hand-grip dynamometer can cost anywhere from $100-$500, while a near infrared system can cost more than $500.

Previously, Kalantar-Zadeh et al. (J Ren Nutr. 2001;11:23-31) demonstrated that measurement with near infrared was a reliable way to determine LBM in HD patients, and Heimburger and colleagues (Am J Kidney Dis. 2000;36:1213-1225) demonstrated a strong correlation between hand-grip strength and LBM as measured by DEXA. Recently, however, a Brazilian group (J Ren Nutr. 2011; 21:235-245) showed that in both men and women receiving HD, hand-grip strength was significantly and inversely correlated with the malnutrition inflammation score (MIS; r = -0.36). The MIS is a well-validated tool to assess nutritional status in HD patients and a higher score indicated worse nutrition status.

In this group of 274 men and 162 women on HD, women were found to have lower levels of hand-grip strength and correspondingly higher scores of the MIS. In fact, this study found that each one standard deviation decrease in hand-grip strength was associated with a two-fold increased risk of an MIS score of 6 or greater.

Clinically feasible options

Finally, in a recent publication by Noori et al (Am J Kidney Dis. 2010;57:130-139) LBM determination was assessed by developing clinically feasible equations. Mid-arm muscle circumference (MAMC: a skinfold measurement), serum creatinine (a marker of LBM), and hand-grip strength were tested in two cohorts of dialysis patients and considered as parameters for these equations. The first cohort was used to develop the equations using DEXA as the gold standard for LBM determination. The second cohort was used to test the newly developed equations.

Results of the first cohort study were that mamc, hand-grip strength, and serum creatinine had the strongest correlation to DEXA (r = 0.57, r = 0.52, and r = 0.46, respectively, adjusted for case-mix). The developed equations for these three variables are:

  1. LBM = 0.34 × serum creatinine (mg/dL) + 5.58 ×{1 if female; 0 if male} + 0.30 ×weight (kg) + 0.67 × height (inches) – 0.23 × urea reduction ratio – 5.75
  2. LBM = 9.09 × hand-grip strength unit + 5.15 × {1 if female; 0 if male} + 0.33 ×weight (kg) + 0.74 × height (inches) – 29.06
  3. LBM = 0.28 × mamc (cm)  + 5.52 ×{1 if female; 0 if male} + 0.28 x weight (kg) + 0.82 × height (inches) – 35.30

To test the equations, the researchers determined the associations between equations 1 and 3 to near infra-red measurements in the second cohort of 612 HD patients and found both to accurately assess LBM. They did not test the hand-grip strength equation in the second portion of the study. This study is very important because now clinicians have a validated equation that can be used to estimate LBM in HD patients.

In conclusion, LBM is an important nutrition status parameter that can now be estimated with validated equations using readily available or easily obtained information. Although guidelines do not currently exist for this type of assessment, it may be reasonable to use the equations annually on stable patients and more frequently in HD patients at high risk for poor nutritional status.

Dr. Steiber is Coordinator of the Dietetic Internship/Master’s Degree Program at Case Western Reserve University in Cleveland.