Performance of rapid test kits to assess household coverage of iodized salt

• Type of Material: Article
• Authors: Jonathan Gorstein, University of Washington; Frits Van Der Haar, Emory University; Karen Codling, Public Nutrition Solutions, Bangkok; Robin Houston, Consultant, Bozeman, MT, USA; Jacky Knowles, Global Alliance for Improved Nutrition (GAIN), Geneva, Switzerland; Arnold Timmer, Global Alliance for Improved Nutrition (GAIN), Geneva, Switzerland
• Language: English
• Date: 2016-10-01
• Publisher: Cambridge University Press (CUP)
• Publication Version: Final Published Version
• Copyright Statement: © The Authors 2016
• License: Creative Commons Attribution-NonCommercial 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1017/S1368980016000938
• Title of Journal or Parent Work: PUBLIC HEALTH NUTRITION
• Volume: 19
• Issue: 15
• Start Page: 2712
• End Page: 2724
• Grant/Funding Information: This work was supported by UNICEF and the US Agency for International Development (USAID). USAID had no role in the design, analysis or writing of this article.
• Keywords: Iodized salt; Titration; Universal salt iodization; Iodine; Rapid test kit
• Research Categories: Health Sciences, Public Health; Health Sciences, Nutrition

Abstract

Objective The main indicator adopted to track universal salt iodization has been the coverage of adequately iodized salt in households. Rapid test kits (RTK) have been included in household surveys to test the iodine content in salt. However, laboratory studies of their performance have concluded that RTK are reliable only to distinguish between the presence and absence of iodine in salt, but not to determine whether salt is adequately iodized. The aim of the current paper was to examine the performance of RTK under field conditions and to recommend their most appropriate use in household surveys. Design Standard performance characteristics of the ability of RTK to detect the iodine content in salt at 0 mg/kg (salt with no iodine), 5 mg/kg (salt with any added iodine) and 15 mg/kg (‘adequately’ iodized salt) were calculated. Our analysis employed the agreement rate (AR) as a preferred metric of RTK performance. Setting/Subjects Twenty-five data sets from eighteen population surveys which assessed household iodized salt by both the RTK and a quantitative method (i.e. titration or WYD Checker) were obtained from Asian (nineteen data sets), African (five) and European (one) countries. Results In detecting iodine in salt at 0 mg/kg, the RTK had an AR>90 % in eight of twenty-three surveys, while eight surveys had an AR<80 %. When the RTK was used for detecting adequately iodized salt, the AR decreased significantly, with only one of fourteen surveys achieving an AR>90 %. Conclusions The RTK is not suited for assessment of adequately iodized salt coverage. Quantitative assessment, such as by titration or WYD Checker, is necessary for estimates of adequately iodized salt coverage.