Evaluating the Effectiveness of the Rapid Test Kit Used in the Field Monitoring Of Iodine Content of Salt in the Philippine Market

Abstract

Abstract— With its ease of use and the minimal training required, the Rapid Test Kit (RTK) has been found to be suitable for field monitoring of compliance to government programs promoting salt iodization in the Philippines and in other countries. The test consists of adding two drops of the test solution on the surface of the salt and comparing the resulting color with the color chart included in the kit.

It has been shown that the colors in the accompanying chart simply do not match with those observed when test solutions are applied on the samples. The tests resulted to colors representing different shades of purple while the existing color chart in RTK presents shades of gray. A scoring system based on different shades of purple was used to quantify the results and allow the conduct of statistical analysis.

To further evaluate the effectiveness of the RTK to distinguish the different levels of iodization in the salt i.e. non-iodized (5ppm and below), inadequately iodized (10, 15, 20 and 25 ppm) and adequately iodized (30, 35 and 44ppm), experimental design and measurement system capability (Attribute Gage Repeatability and Reproducibility or Gage R&R) analyses were undertaken.

Results from the experimental design show that the type of salt used -- whether Local Solar, Imported Solar, Pure Dried Vacuum (PDV) or Cooked Salt – do not affect the resulting color (score) when the test solution is applied. There is no ‘type of salt effect’ and only the amount of iodine in the salt contributes to the variation in the shades of purple observed.

Further, the tests showed that inspectors had difficulty assessing samples within the inadequately iodized range. Iodine concentration levels at the lower rung of this range tend to be misclassified as ‘poorly iodized’ while those at the upper end of the range tend to be judged as ‘adequately iodized’.

From the results of the experiments, three Reference Charts (5 ppm, 30 ppm and chart containing both colors for 5 ppm and 30 ppm) were proposed to replace the existing ineffective chart. These charts were evaluated in their ability to discriminate between the different levels of salt iodization.

Of the 3 proposed Reference Charts tested, the one involving one color only for 5 ppm is the most effective i.e. high percentage of agreement between inspectors on their judgements and that their judgements match the actual iodine concentration levels.

If the government will continue to use the RTK measurement system, the reference chart for one color for 5 ppm is the preferred replacement for the existing chart. However, its limitation should be recognized in that it can only confidently state that a salt sample is either ‘poorly iodized’ or at the very least, inadequately iodized.

Keywords— Rapid Test Kit, Measurement System Capability, Salt Iodization