Table 2.
Linear mixed models for the change in height SDS over 12 months with a time unit of 12 months or 3 months when computing the true mean daily rhGH dose and mean number of injections per week (corresponding to a total of 685.2 patient years, or 2741 patient trimesters).
| 12-month model | 3-month model | |||||
|---|---|---|---|---|---|---|
| Height SDS | % of patients.years | Coeff. [95%CI] | p | % of patients.trimester | Coeff. [95%CI] | p value |
| Constant = mean height at the onset of rhGH treatment | -2.096 [-2.479; -1.713] | <0.001 | -2.058 [-2.452; -1.664] | <0.001 | ||
| Low midparental height (<median for the cohort) | -0.186 [-0.427; 0.056] | 0.132 | -0.215 [-0.463; 0.034] | 0.091 | ||
| Indication (reference category: isolated GHD) | ||||||
| complex GHD | 0.246 [-0.243; 0.735] | 0.324 | 0.254 [-0.246; 0.753] | 0.320 | ||
| small for gestational age | -0.493 [-0.746; -0.240] | <0.001 | -0.497 [-0.757; -0.238] | <0.001 | ||
| Turner syndrome | -0.260 [-0.700; 0.180] | 0.247 | -0.273 [-0.723; 0.176] | 0.234 | ||
| Age at initiation of rhGH treatment (+1 year) | 0.014 [-0.018; 0.047] | 0.389 | 0.010 [-0.023; 0.044] | 0.547 | ||
| Puberty (yes/no) | 0.068 [-0.072; 0.208] | 0.343 | 0.083 [-0.045; 0.210] | 0.204 | ||
| Time effect (+1 year) for rhGH dose>0.03 mg/kg/d and>5 inj/week (ref) | 27% | 0.372 [0.324; 0.432] | <0.001 | 45% | 0.384 [0.336; 0.444] | <0.001 |
| Change in time effect if rhGH dose>0.03 mg/kg/d and 3 to 4 inj/week | 9% | 0.012 [-0.036; 0.048] | 0.643 | 4% | 0.000 [-0.024; 0.024] | 0.82 |
| Change in time effect if rhGH dose>0.03 mg/kg/d and<3 inj/week | 7% | -0.012 [-0.060; 0.036] | 0.675 | 2% | -0.024 [-0.048; 0.012] | 0.22 |
| Change in time effect if rhGH dose<0.03 mg/kg/j and>5 inj/week | 7% | 0.048 [0.000; 0.096] | 0.072 | 11% | 0.000 [-0.012; 0.024] | 0.527 |
| Change in time effect if rhGH dose<0.03 mg/kg/j and 3 to 4 inj/week | 13% | 0.012 [-0.012; 0.048] | 0.357 | 8% | 0.000 [-0.024; 0.012] | 0.80 |
| Change in time effect if rhGH dose<0.03 mg/kg/j and<3 inj/week | 36% | -0.036 [-0.060; 0.00] | 0.044 | 30% | -0.012 [- 0.024; 0.004] | 0.131 |
| Change in time effect if rhGH treatment duration>2 years | -0.024 [-0.060; 0.012] | 0.168 | -0.024 [-0.036; 0.000] | 0.047 | ||
| Change in time effect if puberty | -0.048 [-0.1008; 0.002] | 0.061 | -0.048 [-0.096; -0.002] | 0.040 | ||
| Change in time effect if low midparental height | -0.054 [-0.119; 0.012] | 0.108 | -0.048 [-0.108; 0.024] | 0.190 | ||
Coeff.: coefficient; inj: injection. There was no significant interaction between time and the cause of short stature. The time effect described the effect of one year of rhGH treatment on the height SDS. Ref = reference category. Even in the 3-month model, the time effect was extrapolated to 12 months for easier comparisons of the two models