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• The proportion of patients treated with IG, per disease.
• The dosage used per treatment (g/kg) and the frequency of treatment
(per patient or per year for maintenance treatment).
The source studies were selected according to the following criteria: studies including
data from 1995 onwards, having a large study population size (>1 million inhabitants
mostly), and carried out in Western EU countries - or in other industrialized countries
when other EU studies were not available. When disease rates vary significantly per
geographical area (e.g. prevalence of multiple sclerosis varying with latitude), we have
only consider studies conducted in similar geographical areas.
The values found for the proportion of patient treated with IG, the dosage used per
treatment and the frequency of treatment were discussed and validated in two expert
meetings. For a few indications, the annual numbers of cases were found in Belgian
databases (e.g. transplants). Similarly, the dosage and frequency of administration
obtained through the survey in Belgian hospitals were used when considered as
methodologically reliable and representative, based on expert opinion and information
on current practice.
Estimation of the annual IG amounts per disease
The annual IG quantities estimated to treat these 12 diseases in Belgium were calculated
based on the following:
• Data from other countries were aggregated to produce averages for
incidence or prevalence rate, proportion of patients treated and
frequency of treatment, after being weighted by survey size (“weighted
average”).
• The expected annual number of cases under treatment in Belgium was
calculated by multiplying the weighted average of the incidence or
prevalence rate by the Belgian population size (per age group when
relevant) and by the proportion of patients treated with IG.
• The IG amount used per patient and per year was obtained by multiplying
the average dosage per treatment (in g/kg) by the average body weight
(per age group when relevant) and the frequency of treatment (when
multiple doses are given), named as “method A”. An alternative
estimation (method B) was based on the average IG amounts per case and
per year found in studies from other countries (weighted average), see
Table 24.
• The annual quantities needed to treat each disease were obtained by
multiplying the annual number of patients under treatment by the IG
amount used per patient (by method A and B).
Estimates found for the above indicators are described below. The annual IG quantities
estimated to treat these 12 diseases in Belgium are described in Table 40 and below.
3.3.3.2 Estimates per disease
Idiopathic Thrombocytopenic Purpura
Idiopathic thrombocytopenic purpura (ITP) can present as acute or chronic disease;
chronic disease is defined by a duration of ITP for more than 6 months. Studies on the
incidence of acute and chronic ITP show variations in case definition (especially in terms
of threshold for platelet count) and age studied. These directly influences incidence
estimates as a very sensitive threshold for platelet counts overestimates the frequency
of clinical ITP, and the frequency of chronic ITP increases with age.
IN CHILDREN
Three studies in Norway, Germany and Nordic countries, estimated the incidence rate
of acute ITP in children using similar criteria (bleeding +/- platelet count