Evaluation and assessment of high sensitivity thyrotropin methods as an index for thyroid function

We report the evaluation of four new commercially available sensitive assay kits for determination of thyrotropin (TSH) and their clinical utility in normal subjects and patients with thyroidal and non-thyroidal illnesses. The sensitivity for the reliable detection of serum TSH by these methods ranged from 0.1-0.4 mU/L and their decreasing order was : NML greater than Serono greater than Abbott EIA greater than Hybritech. The coefficient of variation ranged from 2.0-5.8% for intra-assay and 2.3-8.6% for interassay at different concentration levels. Patients studied (n = 130) were assigned into four groups on the basis of the serum thyroxine value and their clinical findings. In total, there were 17 discrepancies (five with Hybritech, three with NML, five with Abbott EIA, and four with Serono) in making the correct diagnosis using these sensitive TSH methods as a single diagnostic test. These discrepancies were mainly in the same patients who were clinically euthyroid but had subnormal TSH values. There were no discrepancies in making the correct diagnosis for patients with hyperthyroidism or hypothyroidism using these sensitive TSH methods. Our observations indicate that the sensitive TSH methods are reliable in measuring subnormal levels and may be used to detect hyperthyroidism without affecting in any way their value in detecting hypothyroidism.