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Correspondence

Indian Pediatr 2017;54: 973-974

Bone Mineral Density in Cystic Fibrosis: Few Concerns: Author's Reply

 

Sumita Gupta and *SK Kabra

Department of Pediatrics, AIIMS, New Delhi, India.
Email: [email protected]

 
 


We are thankful to the author for his interest in our study [1]. The concern regarding self-assessment of pubertal growth is well noted. However, many children may not consent for detailed examination, and self-assessment may be acceptable [2]. It may be possible that few of the subjects may have not interpreted their pubertal stage correctly, but the influence of this misinterpretation was assumed to have influenced both the groups equally.

Physical activity level was estimated using HAES only for Cystic fibrosis patients. Several factors such as nutrition, pulmonary function, physical activity, puberty and glucocorticoids affect bone mineral density (BMD) in patients. Therefore, lower physical activity may only be a partly contributing for the difference in BMD and bone mineral apparent density (BMAD) of the two groups.

Due to word limit in main manuscript we were unable to provide details of measuring BMD and BMAD. DXA scan (Hologic QDR 4500A, Hologic Inc., Bedford, MA, USA) was performed of whole body using standard positioning techniques (as mentioned in the manufacturers manual). The measurements taken were: (i) Whole body bone mineral content (in g); (ii) Whole body bone mineral area (in cm2); (iii) Whole body bone mineral density (in g/cm2). BMAD was calculated for lumbar spine and whole body using the methods suggested by Katzman, et al. [3]. Quality control procedure, which included whole body (Hologic WB # 1252) phantom scanning before subject evaluation, was completed prior to testing on each testing day and it remained stable during the entire study period. In addition to this, short term precision error for the DXA scans was calculated by triplicate measurement of 15 healthy subjects as per the method suggested by Glûer, et al. [4]. Re-positioning of the subjects was done between measurement and single trained technician performed and analyzed all the scans to avoid inter-personnel variations; the person was blinded to the subject’s group (Cystic fibrosis/Control). The calculated coefficient of variation of whole body was 1.3% for BMD.

References

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

2. Marshall WA, Tanner JM. Variations in the pattern of pubertal change in boys. Arch Dis Child. 1970;45:13-23.

3. Katzman DK, Bachrach LK, Carter DR, Marcus R. Clinical and anthropometric correlates of bone mineral acquisition in healthy adolescents girls. J Clin Endocrinol Metab. 1991;73:1332-9.

4. Glûer CC, Blake G, Lu Y, Blunt BA, Jergas M, Genant HK. Accurate assessment of precision errors: How to measure the reproducibility of bone densitometry techniques. Osteoporos Int. 1995;5:262-70.

 

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