Existing empiric equations applied in the current study. The table provides information about the population in which the equations are developed, type of BIA instrument and reference method used as well as components included in the various equations.
Components included in equation
Author (year) / Population developed / BIA instrument / Phase-sensitive / Reference method / Equation / Sex / Age / Weight / Height / R / Xc
Bosy-Westphal (2013) (“Manufacturer’s equation”, segmental BIA) (1) / Healthy adults (18-65 years) with BMI; 18.5-35.0 kg/m2 (n=124) / Segmental MF-BIA (SecamBCA515,Seca, Birmingham, United Kingdom) / x / Four-compartment model (ADP, D2O, DXA) / Unknown1 / x / x / x / x / x / x
Unknown (“Manufacturer’s equation”, whole-body BIA) / Unknown / Whole-body SF-BIA (BIA-model 101, SMT Medical,Würzburg, Germany) / x / Unknown / Unknown1
Kyle (2001) (“The Geneva equation”) (2) / Healthy adults (20-94 years) with BMI; 17.0-33.8 kg/m2 (n=343) / Whole-body SF-BIA (Xitron 4000B, Xitron Technologies, San Diego, CA, USA) / x / DXA (Hologic QDR-4500) / FFM = -4.104 + (0.518 x Ht2/R50) + (0.231 x weight) + (0.130 x Xc50) + (4.229 x sex) / x / x / x / x / x
Lukaski (1986) (3, 4)2 / Healthy adults (18-50 years) with FFM; 34.4-96.3 kg (n=114) / Whole-body SF-BIA (RJL-model 101, RJL Systems, Detroit, MI, USA) / x / Densitometry / FFM = (0.810 x Ht2/R50) + 6.39 / x / x
Lukaski* (1986) (3)2 / Healthy adults (18-50 years) with FFM; 34.4-96.3 kg (n=114) / Whole-body SF-BIA (RJL-model 101, RJL Systems, Detroit, MI, USA) / x / Densitometry / FFM for men = (0.827 x Ht2/R50) + 5.214
FFM for women = (0.821 x Ht2/R50) + 4.917 / x / x
Segal* (1988) (5)3 / Healthy adults
(17-62 years) with FM; 3.0-56.0 % (n=1567) / Whole-body SF-BIA (Unknown model, RJL Systems, Detroit, MI, USA) / x / Densitometry / FFM for men = (0.00132 x Ht2) – (0.04394 x R50) + (0.30520 x weight) – (0.16760 x age) + 22.66827
FFM for women = (0.00108 x Ht2) – (0.02090 x R50) + (0.23199 x weight) – (0.06777 x age) + 14.59453 / x / x / x / x
Heitmann (1990) (4, 6)4 / Healthy adults (35-65 years) (n=139) / Whole-body SF-BIA (RJL-model 103, RJL Systems, Detroit, MI, USA) / x / Four-compartment model (Body potassium (whole body counting) and total body water (dilutometry)) / FFM = (0.295 x Ht2/R50) + (0.204 x weight) + (5.009 x sex) – (0.076 x age) + (0.227 x Ht) – 17.04 / x / x / x / x / x
Heitmann* (1990) (4, 6)4 / Healthy adults (35-65 years) (n=139) / Whole-body SF-BIA (RJL-model 103, RJL Systems, Detroit, MI, USA) / x / Four-compartment model (Body potassium (whole body counting) and total body water (dilutometry)) / FFM for men = (0.244 x Ht2/R50) + (0.270 x weight) + (0.284 x Ht) - 28.02
FFM for women = (0.411 x Ht2/R50) + (0.141 x weight) + (0.267 x Ht) - 28.61 / x / x / x
Deurenberg (1990) (7) / Healthy adults (60-83 years) (n=72) / Whole-body SF-BIA (RJL-model 101, RJL Systems, Detroit, MI, USA) / x / Densitometry / FFM = (0.671 x Ht2/R50) + (3.1 x sex) + 3.9 / x / x / x
Deurenberg (1991) (8, 9)5 / Healthy adults (>16 years) (n=661) / Whole-body SF-BIA (RJL-model 101, RJL Systems, Detroit, MI, USA) / x / Densitometry / FFM = (0.340 x Ht2/R50) + (0.1534 x Ht) + (0.273 x weight) – (0.127 x age) + (4.56 x sex) - 12.44 / x / x / x / x / x
Lohman* (1988) (10, 11)6 / Healthy adults (18-29 years) (n=153) / Whole-body SF-BIA (Unknown model, Valhalla Scientific, San Diego, CA, USA) / Unknown / Densitometry / FFM for men = (0.485 x Ht2/R50) + (0.338 x weight) + 5.32
FFM for women = (0.475 x Ht2/R50) + (0.295 x weight) + 5.49 / x / x / x
Schols* (12)7 / COPD patients (n=117) / Whole-body SF-BIA (Unknown manufacturer and model) / Unknown / Dilutometry / FFM for men: 8.383 + (0.465 x Ht2/R50) + (0.213 x weight)
FFM for women: 7.610 + (0.474 x Ht2/R50) + (0.184 x weight) / x / x / x
Kyle (1998) (13) / Ambulatory patients with severe chronic respiratory insufficiency (45-86 years); BMI < 32.0 kg/m2 (n=75) / Whole-body SF-BIA (Bio-Z®, New Cardiocorp, Fribourg, Switzerland) / x / DXA (Hologic CDR-2000®) / FFM = -6.06 + (Ht x 0.283) + (weight x 0.207) - (R50 x 0.024) + (sex x 4.036) / x / x / x / x
Gray* (1989) (14) / Healthy adults (19-74 years) with BMI; 19.6-53.3 kg/m2 (n=87) / Whole-body SF-BIA (RJL-model101, RJL Systems, Detroit. MI, USA) / x / Densitometry / FFM for men = (0.00139 x Ht2) – (0.0801 x R50) + (0.187 x weight) + 39.830
FFM for woman = (0.00151 x Ht2) – (0.0344 x R50) + 0.140 x weight – (0.158 x age) + 20.387 / (x) / x / x / x
*Indicates gender-specific equations; women=0, men=1. None of the equations tested included anthropometric measures (e.g. thigh or ankle circumference).
1Both the equations incorporated into the whole-body BIA and segmental BIA were unknown. However, for segmental BIA the components were known.
2The equation tested was developed in 47 male volunteers andcross-validated against a previous linear regression equation developed in 37 male volunteers(15). The results of the cross-validation showed no significant difference between the slopes or the intercepts of the individual regression lines. Furthermore, no significant difference was found between the slopes or the intercepts of the individual regression lines for males (n=84) and females (n=67).
3The equation tested is the best-fitting regression line from 4 laboratories pooled but with separate equations for men and women. A quadruple cross-validation was performed to determine the reproducibility across laboratories of the relationship between densitometrically determined FFM and FFM predicted from BIA and other variables.
4The equation is taken from the supplementary material of the review article by Haverkortet al (2015) (4). The original article by Heitmannet al (1990)(6)is not available at (abstract only).
5The original article by Deurenberget al(8) is not available at (abstract only). The equation used in the present study is taken from the review article by Kyle et al (2004) (9).
6The equation tested (“The Lohman equation”) is taken from an article by Graves et al (1989) (11) referring to unpublished results from the 1986 Valhalla inter-laboratory investigation of BIA (10).
7The equation tested (“The Schols* equation”) is taken from an article by Steiner et al (2002) (12) referring to sex-specific regression equations derived from Scholset al (University of Maastricht, Maastricht, the Netherlands) (personal communication).
Abbreviations: BIA; Bioelectrical impedance analysis, DXA; Dual energy x-ray absorptiometry, ADP; Air displacement plethysmography, D2O; Deuterium oxide,SF; Single-frequency, MF; Multi-frequency, BMI; Body mass index, FFM; Fat free mass, FM; Fat mass, COPD; Chronic obstructive pulmonary disease, Ht; Height,R50; Resistance at 50 kHz, Xc; reactance at 50 kHz.
References
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10.Lohman TG. Preliminary results from the 1986 Valhalla interlaboratory investigation on bioelectrical impedance. Unpublished data. 1988.
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