Comparison of two methods to categorize thickened liquids for dysphagia management in a clinical care setting context: The Bostwick consistometer and the IDDSI Flow Test. Are we talking about the same concept?
Authors: Côté Claudia , Germain Isabelle , Dufresne Thérèse , Gagnon Cynthia 
Published: October 2018

The Bostwick consistometer and the International Dysphagia Diet Standardization Initiative (IDDSI) Flow Test are both proposed methods to measure and categorize thickened liquids for dysphagia management. The objectives were to: (a) compare the Bostwick consistometer reference values used in clinical settings and the IDDSI reference values of thickened liquids suggested for nutrition care plans in the management of dysphagia when measuring commercially available preprepared thickened liquids; (b) explore the relationship between the two methods; (c) assess the interchangeability; (d) document the intra‐rater reliability. Preprepared thickened liquids (n = 32) were measured twice with the Bostwick consistometer and 3 times with the IDDSI Flow Test, using a rigorous methodology. A registered dietitian nutritionist and a registered nutrition and dietetic technician performed the measurements. The Pearson's correlation coefficient was calculated to explore the relationship between the two methods. Using a linear regression equation, back‐calculations of the IDDSI Flow Test values were done, based on the experimental Bostwick results. Interchangeability was assessed by documenting the level of agreement between the results with a Bland and Altman graphical analysis. Intraclass correlation coefficients calculation and a Bland and Altman graphical analysis were performed to assess reliability. The strong correlation (r = −.93, p < .001) between the IDDSI Flow Test and the Bostwick consistometer measurements suggests that they measure flow rate in a similar manner, but not exactly the same, as confirmed with the Bland and Altman graphical analysis. Thus, they produced results that are not interchangeable. However, both tests show excellent intra‐rater reliability (ICC ≥ 0.99) when using a rigorous methodology.

Practical applications

Thickened liquids are used to manage oropharyngeal dysphagia. Clinicians need to provide quality assurance/quality control (QA/QC) support in the selection or production of thickened liquids as well as staff training or patient education regarding these products. Methods and classification have been proposed to measure and categorize thickened liquids for dysphagia management, such as the line spread test, the Bostwick consistometer method, and the IDDSI Flow Test. Although empirical, these methods are more accessible to clinicians than viscometer or rheometer assessments. Clinicians need to understand the limitations of these techniques as neither appear to capture the full extent of consistency for potential beverages available on the market or produced in‐house. In this article, we compare the Bostwick consistometer and the IDDSI Flow Test methods and classifications and propose a standard operating procedure in order to maximize the quality of results. We point out the large variations in consistency levels of commercial preprepared thickened liquids in light of the absence of evidence of clinical outcomes associated with either proposed methods or consistency classifications.