Comparative study of IDDSI flow test and line-spread test of thickened water prepared with different dysphagia thickeners

The flow behaviors of thickened water samples prepared with six commercial instant thickeners (A-F) were investigated at different thickness levels using the inexpensive, simple, and visual clinical tools, such as a line-spread test (LST) and a syringe flow test developed by the International Dysphagia Diet Standardization Initiative (IDDSI). Both the flow distance value measured by the LST and the volume remaining in syringe by IDDSI flow test were compared with the apparent viscosity (ηa,50 ) values measured with a sophisticated computer-controlled rheometer. The ηa,50 values of thickened water samples increased as thickener concentration increased, whereas the flow distance (cm; LST) or remaining volume (ml; IDDSI flow test) were decreased. Plots comparing ηa,50 values to LST flow distances and IDDSI volumes revealed exponential relationships (R2 = 0.926 for the LST and R2 = 0.898 for IDDSI test) between the two measurements. Such lower determination coefficient (R2 ) values (0.898) by IDDSI flow test seems to be due to the stickiness characteristics of starch component in starch-based thickeners (E and F), indicating that the syringe flow test is not suitable for starch-based thickeners. However, the thickened water samples prepared only with xanthan gum (XG)-based thickeners (A-D) showed strong relationships (R2 = 0.972 for the LST and R2 = 0.939 for IDDSI test). These results suggest that the LST is a more reliable method than the IDDSI test for evaluating the correct and desirable viscosity for the dysphagia diet, and that the IDDSI test provides a means to predict the rheometer-measured viscosity of water thickened with only XG-based thickeners. PRACTICAL APPLICATIONS: The effective management of dysphagia requires the thickened fluids prepared with the correct and desirable viscosity. In terms of clinical practice, it is very important to observe the comparison of LST with IDDSI flow test to determine a suitable method for estimating the correct viscosity of thickened fluids. Our results showed good relationships between the rheometer-measured viscosity and flow values measured by the LST and IDDSI test methods for the thickened water samples prepared with different foods thickeners. The IDDSI flow test may be useful as a clinical training tool for preparing thickened fluids with only XG-based thickeners to a target level of viscosity. These results presented in this study will provide clinicians, caregivers, and patients with valuable information for IDDSI flow test as an inexpensive and simple method for measuring the correct viscosity.