Anjum Lqbal, Farooq Ahmad Khan, Anjum lqbal.
Comparison of two sensitive TSH (Thyrotropin) assays for evaluation of thyroid function.
Pak J Pathol Jan ;16(2):52-7.
Introduction: With the development of highly sensitive TSH assays, it is now possible to use TSH as a precise and specific first line test for the diagnosis of thyroid dysfunction and monitoring of the adequacy of thyroid hormone replacement therapy. It is essential to establish analytical/clinical decision limits for TSH assay. Objective: To determine and compare the decision limits for second generation and third generation assays in order to have an optimum sensitivity and specificity. Study design: Prospective, laboratory based. Place of study: Department of Pathology, Naval Hospital Islamabad. Material and Method: Blood samples were collected from adult patients (n=450) of both sexes, suspected of thyroid function disorders. Serum TSH was measured using second generation IMx TSH assay kit along with FT4. T3 was measured in selected casess. Subjects were categorised after both clinical and biochemical assessment based on measurement of TSH, FT4 and T3. Sera of 125 subjects including 33 hyperthyroid, 13 hypothyroid and 79 randomly selected euthyroid subjects were analysed by third generation Immulite TSH assay kit along with FT4 and T3 (in selected cases only) for the comparison of two sensitive thyrotropin assays. Results: There was a statistically significant correlation (r=0.96) between two thyrotropin assays in euthyroid and hypothyroid patients (p<0.0001) but in hyperthyroid patients, statistically insignificant correlation was found between IMx and Immulite TSH assay (r=0.017), p=0.92). ROC curves were also plotted to compare the diagnostic accuracy. Conclusion: Both assays showed almost same diagnostic accuracy in euthyroid and hypothyroid patients but in hyperthyroid patients, lmmulite TSH assay showed better sensitivity, specificity, positive predictive value and negative predictive value.
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