A multicentric study on validation of spot testing kit

To assess the validity of the Spot testing kit (against the Standard iodometric titration) in the semi-quantitative estimation of iodine in salt.

The project was conducted at four centers in the country, namely, Vadodara, Jodhpur, Dibrugarh and New Delhi (AIIMS, coordinating centre). Uniform protocol was utilized at all the four centres. The school going children were asked to bring 30 g of iodine from their kitchen in an auto-seal polythene pouche with an identification slip. The iodine content of 3,010 salt samples (more than 700 salt samples from each center) was estimated independently by two different methods i.e., Iodometric Titration (used as reference standard) and Spot Testing Kit (STK) method, and the results were compared. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the STK method in relation to the Standard iodometric titration (SIT) were calculated.

From total of 3,010 salt samples, majority (98%) of the salt samples collected were of powdered salt. The specificity of various research centers ranged from 60.5% to 88.9%. The positive predictive value of the various research centers ranged from 69.9% to 98%. The NPV of the various research centers ranged from 96.8% to 100%. The pooled sensitivity and specificity of the STK method (against IT method) for four centers together was 99.6% and 66.7%, respectively.

The STK method is reliable for semi quantitative estimation of iodine content in salt and it can be used for monitoring the quality of iodized salt available in the community.