A multi-centric study on establishing reference interval for TSH, TT4 and TT3 in Western India

Direct sampling strategy was used to establish the reference interval, with a total of 425 healthy subjects who were screened medically and by lab tests to exclude cases of subclinical thyroid dysfunction. As per guidelines published by CLSI, non-parametric method was used with ranking of values to get the central 95th percentile as reference interval. The sample size and the need for partitioning gender-wise & age-wise were verified as per tests in CLSI guidelines. Following conclusions were drawn from the results of the study. (a): The sample size was appropriate. (b): The difference between the study and kit insert reference limits were more at the lower limits for TSH and at the upper limits for TT4 and TT3. (c): The difference between the genders was statistically significant for TT4 indicating need to adopt gender-wise reference intervals. (d): Effect of age in the group of 18 to 30 years was significant for TT3; no significant effect of age on TSH and TT4 reference intervals. (e): The upper reference limits for TSH, TT4 and TT3 in the current study, are seen to be more than the international findings and more pronounced for TT4. (f): Based on the NACB’s recommendation for lowering the cut-off of TSH to 2.5 mIU/L, it was observed that there was a significantly high proportion in population with values of TSH more than 2.5 mIU/L.