Gupta, et al.[1] published their study on bone mineral density of Indian children and adolescents with cystic fibrosis in a recent issue of Indian Pediatrics. I seek following clarifications:

Pubertal development was determined by a self-assessment questionnaire in the study. However, validity of self-assessment of pubertal maturation has shown conflicting results. Tanners’ breast, genital and pubic hair classification [2] also did not use self-assessment questionnaire. Rasmussen, et al. [3] concluded in their study that breast stage was assessed correctly by only 44.9% of the girls and genital stage by 54.7% of the boys. For pubic hair stage, 66.8% of girls and 66.1% of boys made correct assessments. Girls underestimated, whereas boys overestimated their pubertal staging. Therefore, pubertal assessment by children/ adolescents is not a reliable measure of exact pubertal staging and should be validated by physical examination.

Physical activity level of patients in this study was estimated using Habitual Activity Estimation Scale (HAES) [4]. Was physical activity estimated for controls too? Was there any significant difference? Difference in bone mineral density (BMD) and bone mineral apparent density (BMAD) may be attributable to differences in physical activity levels between patients and controls.

There was no mention of detailed method of calculation of BMD and BMAD. Patient positioning during procedure is a source of error in repeat bone density tests and data are not always reproducible on repeat tests. Study [1] reports significant differences in both BMD and BMAD in patients and controls. As BMD changes with age in children, only BMAD should have been compared.

1. Gupta S, Mukherjee A, Khadgawat R, Kabra M, LodhaR, Kabra SK. Bone mineral density of indian children and adolescents with cystic fibrosis. Indian Pediatr.　2017;54:545-9.

2. Tanner JM, Whitehouse RH. Clinical longitudinal standards for height, weight, height velocity, weight velocity, and stages of puberty. Arch Dis Child. 1976;51:172-9.

3. Rasmussen AR,　Wohlfahrt-Veje C,　Tefre de Renzy-Martin K,　Hagen CP,　Tinggaard J,　Mouritsen A, et al. Validity　of　self-assessment　of　pubertal　maturation. Pediatrics.2015;135:86-93.

4. Hay JA, Cairney J. Development of the Habitual Activity Estimation scale for clinical research: A systematic approach. Pediatr Exer Sci. 2006;18:193-202.