External validation of a prediction model for estimating fat mass in children and adolescents in 19 countries: individual participant data meta-analysis
Authors: Hudda Mohammed T , Wells Jonathan C K , Adair Linda S , Alvero-Cruz Jose R A , Ashby-Thompson Maxine N , Ballesteros-Vásquez Martha N , Barrera-Exposito Jesus , Caballero Benjamin , Carnero Elvis A , Cleghorn Geoff J , Davies Peter S W , Desmond Malgorzata , Devakumar Delan , Gallagher Dympna , Guerrero-Alcocer Elvia V , Haschke Ferdinand , Horlick Mary , Ben Jemaa Houda , Khan Ashraful I , Mankai Amani , Monyeki Makama A , Nashandi Hilde L , Ortiz-Hernandez Luis , Plasqui Guy , Reichert Felipe F , Robles-Sardin Alma E , Rush Elaine , Shypailo Roman J , Sobiecki Jakub G , ten Hoor Gill A , Valdés Jesús , Wickramasinghe V Pujitha , Wong William W , Riley Richard D , Owen Christopher G , Whincup Peter H , Nightingale Claire M 
Published: September 2022

Objective

To evaluate the performance of a UK based prediction model for estimating fat-free mass (and indirectly fat mass) in children and adolescents in non-UK settings.

Design

Individual participant data meta-analysis.

Setting

19 countries.

Participants

5693 children and adolescents (49.7% boys) aged 4 to 15 years with complete data on the predictors included in the UK based model (weight, height, age, sex, and ethnicity) and on the independently assessed outcome measure (fat-free mass determined by deuterium dilution assessment).

Main outcome measures

The outcome of the UK based prediction model was natural log transformed fat-free mass (lnFFM). Predictive performance statistics of R2, calibration slope, calibration-in-the-large, and root mean square error were assessed in each of the 19 countries and then pooled through random effects meta-analysis. Calibration plots were also derived for each country, including flexible calibration curves.

Results

The model showed good predictive ability in non-UK populations of children and adolescents, providing R2values of >75% in all countries and >90% in 11 of the 19 countries, and with good calibration (ie, agreement) of observed and predicted values. Root mean square error values (on fat-free mass scale) were <4 kg in 17 of the 19 settings. Pooled values (95% confidence intervals) of R2, calibration slope, and calibration-in-the-large were 88.7% (85.9% to 91.4%), 0.98 (0.97 to 1.00), and 0.01 (−0.02 to 0.04), respectively. Heterogeneity was evident in the R2and calibration-in-the-large values across settings, but not in the calibration slope. Model performance did not vary markedly between boys and girls, age, ethnicity, and national income groups. To further improve the accuracy of the predictions, the model equation was recalibrated for the intercept in each setting so that country specific equations are available for future use.

Conclusion

The UK based prediction model, which is based on readily available measures, provides predictions of childhood fat-free mass, and hence fat mass, in a range of non-UK settings that explain a large proportion of the variability in observed fat-free mass, and exhibit good calibration performance, especially after recalibration of the intercept for each population. The model demonstrates good generalisability in both low-middle income and high income populations of healthy children and adolescents aged 4-15 years.