Forty studies (n=106,959) were included in the review: 32 RCTs (n=103,682) and eight CCTs (n=3,277). Seven studies were considered to be high quality, 27 studies were regarded as moderate quality and six studies were considered low quality.
Six studies (n=1,009) reported externally validated clinical measures of disease status. IVRS users showed a non-significant improvement in glycosylated haemoglobin, total cholesterol and serum glucose.
Three studies reported clinical end points that could not be pooled. A study on asthma patients showed no improvement in the IVRS group on acute or routine care visits or on hospitalisation for asthma. Two smaller studies on patients with heart failure showed some improvement in number of cardiac events and time in hospital in the IVRS group.
Fourteen studies that measured objective process adherence outcomes were analysed. The median effect of the IVRS intervention was significant at 7.9% (interquartile range 2.8 to 19.5). A subgroup analysis of eight studies of adherence to immunisation advice showed that those who received the IVRS intervention had significantly higher immunisation rates (OR 1.70, 95% CI 1.41, 2.04, I2=78%.
Twenty-four studies reported a total of 74 patient-reported outcomes that could not be pooled. Two-thirds of outcomes showed no significant differences between IVRS and control groups and one third had outcomes that favoured the IVRS group.
Five studies reported on quality-of-life outcomes. Two of these studies reported that IVRS was associated with significant improvements in general health.