70 healthy subjects, these groups are not comparable. Therefore, results should be interpreted separately and can only be applied to subjects with the same sex and age distribution. Although both patients and healthy subjects performed different tests and filled in questionnaires between test and retest, it is possible that the time between test and retest of approximately 15 minutes (healthy subjects) to 2 hours (patients) has caused some recall bias, because previous research used a 48 hour time frame.12 However, no response shift was found between the second and first test; the second test did not always show an improvement compared to the first test, which otherwise would have been visible in the Bland Altman plots in Figure 1. Therefore, it is believed that this possible bias is negligible. No inter-rater reliabilities were tested, because this was believed to be too time consuming for patients with HNC. In this study, all patients passed the WST and thus showed no signs of dysphagia nor aspiration. This contradicts previous results, which show that up to 84% of patients suffer from dysphagia post-treatment,6 and that the WST has a good sensitivity for the detection of aspiration.13,16 One explanation could be that the WST missed latent or silent aspiration in patients.11,13 In addition, a random selection was made of different patients with HNC before treatment up to two years after treatment. It may be possible to have missed patients with severe dysphagia, because dysphagia is mainly seen 3 and 6 months after treatment,11 and in patients with pharyngeal cancer.14 However, the swallowing speed calculated from the WST provides an effective tool for screening for FEES referral,15 in which dysphagia can be further evaluated.8 Future research The 100 mL WST has been validated using video fluoroscopy in patients with neurogenic dysphagia with a sensitivity and specificity up to 85.5% and 91.7%.15 In patients with motor neuron disease, the WST had a high inter-rater reliability, with bigger differences between subjects due to the effects of age and sex.19 The high sensitivity, specificity and inter-rater reliability indicate that the WST is an excellent test to use when measuring swallowing performance. These findings are equally important as the reliability testing performed in this research, and should be taken into account as well when reporting outcome measures on swallowing performance. The results of the test-retest reliability can be used in future research to provide insight into differences over time and differences between different treatment modalities for patients with HNC. Swallowing volume was significantly different between test and retest for patients with HNC. In addition, swallowing speed in healthy subjects had a moderate reliability while all other ICCs show a good to excellent reliability, and duration had a
RkJQdWJsaXNoZXIy MjY0ODMw