Comparison of weight- vs body surface area-based growth hormone dosing for children: implications for response.

OBJECTIVE: To compare weight (per kg)- vs body surface area (BSA, per m(2) )-based growth hormone (GH) dosing formats in children and to derive a useful conversion formula between the two formats. PATIENTS AND
DESIGN: Growth hormone doses (>33,000) from 1874 children were obtained from the national Australian database (OZGROW) and used to derive conversion formulae and to confirm the accuracy of a conversion formula based on a weight-only BSA estimate. A further 27,000 doses were used to test the accuracy of all formulae. The best conversion formula was used to compare weight- and surface area-based GH dosing, which included an analysis of first year response (∆SDS height or growth velocity, GV). MEASUREMENTS: Growth hormone doses in mg/m(2) /wk and mg/kg/wk, dose estimates, residuals, first year ∆SDS, first year GV.
RESULTS: The formula, [Formula: see text] based on a weight-only BSA estimate, provides accurate dose conversion (mean residual, 0·005 mg/kg/week). A constant mg/m(2) /week dose expressed in terms of mg/kg/week declines quickly with increasing body weight to approximately 15 kg after which the decline continues although less dramatically. For Australian patients, despite an increase in mean per m(2) dose with increased starting weight/age, the per kg dose decreased. This was associated with a greater decline in first year GV than estimated if a per kg dose had been maintained.
CONCLUSIONS: Growth hormone doses can be accurately converted between formats. Surface area-based GH dosing is likely to result in a reduced height response as children become heavier when compared with weight-based GH dosing.