Reply to LM Klevay

Departments of Pediatrics and Obstetrics and Gynecology
Hutzel Hospital
Wayne State University
4707 St Antoine Boulevard
Detroit, MI 48201
E-mail: wkoo{at}wayne.edu

Dear Sir:

We appreciate Klevay's interest in our report comparing the values obtained with the pencil-beam and fan-beam dual-energy X-ray absorptiometry (DXA) techniques in piglets and human infants (1). It is true that the regression analysis indicated that the measurement by one technique had a strongly significant linear relation with the measurement by the other. However, it is important to reiterate our statement that a strong correlation does not necessarily indicate identical results, because the absolute values obtained from these 2 techniques differed significantly. Our data indicated that group comparison of pencil-beam and fan-beam data is possible only if either set of data is adjusted, and caution is required in comparing individual data points. It is advisable that normative data be generated separately for each technique and that the same technique be used throughout longitudinal studies.

We did take the opportunity to perform other studies using the piglet model. We reported the validation of whole-body scans with the use of both the pencil-beam (2) and the fan-beam (3, 4) DXA techniques by using whole-carcass chemical analysis for ash, calcium, nitrogen, and fat. We also validated regional scans by using both DXA techniques with chemical measurements of humeri andfemora (5). Furthermore, we validated the DXA bone mass measurements with functional outcome by showing their strong predictability for bone strength (6).

REFERENCES

1. Koo WWK, Hammami M, Hockman EM. Interchangeability of pencil-beam and fan-beam dual-energy X-ray absorptiometry measurements in small subjects. Am J Clin Nutr 2003;78:236–40.
2. Koo WWK, Hammami M, Hockman EM. Validation of bone mass and body composition measurements in small subjects with pencil beam dual energy X-ray absorptiometry. J Am Coll Nutr 2004;23:79–84.
3. Koo WWK, Hammami M, Hockman EM. Use of fan beam dual energy X-ray absorptiometry to measure body composition of piglets. J Nutr 2002;132:1380–3.
4. Chauhan S, Koo WWK, Hammami M, Hockman EM. Fan beam dual energy X-ray absorptiometry body composition measurements in piglets. J Am Coll Nutr 2003;22:408–14.
5. Hammami M, Koo MWM, Koo WWK, Thomas RT, Rakhman D. Regional bone mass measurement from whole body dual energy x-ray absorptiometry scan. J Clin Densitom 2001;4:131–6.
6. Koo MWM, Yang KH, Begeman P, Hammami M, Koo WWK. Prediction of bone strength in growing animals using non-invasive bone mass measurements. Calcif Tissue Int 2001;68:230–4.