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## Background

An accurate assessment of the lean the body weight (LBW) is essential in order to ensure greater accuracy in drug prescribing especially in the field of oncology where there is a significant risk of adverse effects.

Key points:

• Lean body weight decreases with increasing age, while the body fat percentage increases.
• Total body weight consists of fat free mass (FFM) plus fat mass (FM). FFM includes bone, muscle, vital organs and extracellular fluid. LBW also includes the lipid in cellular membranes which leads to a small difference between LBW and FFM of approximately 3% in men and 5% in women. Many experts consider FFM to =~ LBW.
• The BMI has several limitations including the inability to account for the differences in body composition of multiple ethnic groups as well as an inability to differentiate between changes in lean mass versus changes in body fat. The BMI reflects changes in mass only.
• LBM = BW - BF
Lean body mass equals body weight minus body fat

## Nyman U. James Lean Body Weight Formula Is Not Appropriate for Determining CT Contrast Media Dose in Patients with High Body Mass Index. Radiology. 2016 Mar;278(3):956-7. doi: 10.1148/radiol.2016152031. PMID: 26885737.

• It should, however, be noted that, with the James formula, estimated LBW reaches a plateau at a BMI of about 37 and 43 kg/m2 in women and men, respectively. Estimated LBW then decreases with increasing BMI and approaches zero in severely obese individuals due to the construction of the formula with a quadratic term for weight-to-height ratio.
• Instead, contrast material dose based on, for example, the Boer formula (5), with its linear function, may be more appropriate because estimated LBW increases steadily with increasing BMI.
• Thus, the James formula should not be used as a base for contrast material dose at CT in patients with a high BMI. Instead, formulas like the Boer formula may be more appropriate, though correlation between its estimated LBW and contrast material enhancement must be evaluated-especially in patients with a high BMI.

Age: years

Height:

Weight:

Gender:

## Boer Equation:

LBM (men) = 0.407 * weight [kg] + 0.267 * height [cm] - 19.2

LBM (women) = 0.252 * weight [kg] + 0.473 * height [cm] - 48.3

Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984 Oct;247(4 Pt 2):F632-6. doi: 10.1152/ajprenal.1984.247.4.F632. PMID: 6496691. https://pubmed.ncbi.nlm.nih.gov/6496691/

## James Formula:

Women: 1.07 * weight [kg]  - 148 * (weight [kg] /height [cm])2

Men: 1.10 * weight [kg]  - 128 * (weight [kg] /height [cm])2

Nyman U. James Lean Body Weight Formula Is Not Appropriate for Determining CT Contrast Media Dose in Patients with High Body Mass Index. Radiology. 2016 Mar;278(3):956-7. doi: 10.1148/radiol.2016152031. PMID: 26885737.

## Hume Equation

For men: LBM = (0.32810 * Wt[kg]) + (0.33929 * Ht [cm]) - 29.5336

For women: LBM = (0.29569 * Wt[kg]) + (0.41813 * Ht [cm]) - 43.2933

Hume, R (Jul 1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology. 19 (4): 389-91. doi:10.1136/jcp.19.4.389.

## References

1. Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984 Oct;247(4 Pt 2):F632-6. doi: 10.1152/ajprenal.1984.247.4.F632. PMID: 6496691. https://pubmed.ncbi.nlm.nih.gov/6496691/
2. Heitmann BL: Evaluation of body fat estimated from body mass index, skinfolds and impedance. A comparative study. Eur J Clin Nutr. 1990, 44 (11): 831-837.
3. Hume, R (Jul 1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology. 19 (4): 389-91. doi:10.1136/jcp.19.4.389.
4. Janmahasatian S, Duffull SB, Ash S, Ward LC, Byrne NM, Green B: Quantification of lean bodyweight. Clin Pharmacokinet. 2005, 44 (10): 1051-1065. 10.2165/00003088-200544100-00004.

5. Kim CH, Chung S, Kim H, Park JH, Park SH, Ji JW, Han SW, Lee JC, Kim JH, Park YB, Nam HS, Kim C. Norm references of fat-free mass index and fat mass index and subtypes of obesity based on the combined FFMI-%BF indices in the Korean adults aged 18-89 yr. Obes Res Clin Pract. 2011 Jul-Sep;5(3):e169-266. doi: 10.1016/j.orcp.2011.01.004. PMID: 24331103.

6. Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995 Oct;5(4):223-8. doi: 10.1097/00042752-199510000-00003. PMID: 7496846. [Normalized FFMI]
7. Kyle UG, Schutz Y, Dupertuis YM, Pichard C. Body composition interpretation. Contributions of the fat-free mass index and the body fat mass index. Nutrition. 2003 Jul-Aug;19(7-8):597-604. doi: 10.1016/s0899-9007(03)00061-3. PMID: 12831945.

8. Lee, K., Lee, S., Kim, S.Y. et al. (2007) Percent body fat cutoff values for classifying overweight and obesity recommended by the International Obesity Task Force (IOTF) in Korean children. Asia Pacific Journal of Clinical Nutrition, 16, 649-655.

9. Mittal, R. , Goyal, M. , Dasude, R. , Quazi, S. and Basak, A. (2011) Measuring obesity: results are poles apart obtained by BMI and bio-electrical impedance analysis. Journal of Biomedical Science and Engineering, 4, 677-683. doi: 10.4236/jbise.2011.411084.

10. Nyman U. James Lean Body Weight Formula Is Not Appropriate for Determining CT Contrast Media Dose in Patients with High Body Mass Index. Radiology. 2016 Mar;278(3):956-7. doi: 10.1148/radiol.2016152031. PMID: 26885737.

11. Schutz, Y., Kyle, U. & Pichard, C.. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. Int J Obes Relat Metab Disord. 2002; 26(7):953-60. https://doi.org/10.1038/sj.ijo.0802037

12. Yu, S., Visvanathan, T., Field, J. et al. Lean body mass: the development and validation of prediction equations in healthy adults. BMC Pharmacol Toxicol 14, 53 (2013). https://doi.org/10.1186/2050-6511-14-53.

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