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Chapter 2.2
50
p=0.002). Previous IFN therapy resulted in a signifi cantly lower chance of sustained
response in patients with genotype A or D (OR 0.21 [0.07 – 0.58], p=0.003). We found no
differences in the predictors of response for the two treatment groups.
Performance of the model
The distribution of the predicted probabilities of sustained response in genotypes A
– D is shown in fi gure 1. The agreement between the predicted probabilities and the
observed frequency of sustained response was good (p=0.27 by the Hosmer–Lemeshow
goodness-of-fi t test). A multivariable model including the variables age, sex, ALT, HBV
DNA, HBV genotype and previous interferon therapy had adequate discriminative
ability as shown by an area under the receiver-operating characteristic curve (AUC) of
0.72 (95%-CI, 0.67 – 0.77). The AUC was 0.75 (95%-CI, 0.65 – 0.85), 0.65 (95%-CI, 0.55
– 0.75), 0.68 (95%-CI, 0.61 – 0.75) and 0.78 (95%-CI, 0.65 – 0.92) for genotypes A to D,
respectively. After bootstrap validation, the area under the ROC curve was 0.69 (95%-
CI, 0.60 – 0.77). Since the infl uence of the predictors was signifi cantly different across
genotypes, a validated formula for the prediction of sustained response was generated
for each HBV genotype separately. The PEG-IFN HBV Treatment Index is based on these
formulas (fi gure 2). An automated calculator can be found on www.liver-gi.nl/peg-ifn.
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Figure 1. Distribution of predicted probabilities of sustained response in patients with HBV genotype A-D.
Boxplots show the distribution of the predicted probabilities of sustained response, defi ned as HBeAg
loss and HBV DNA