Comparison of Kodak Amerlite FT4 and TSH-30 with T4 and TSH as first-line thyroid function tests

To evaluate the effect of test automation and a change in strategy for thyroid function tests (TFT) on personnel needs and turn-around time. The first-line TFT were changed from T4 and TSH to FT4 and TSH-30.

Samples received for TFT from 357 randomly selected patients were analyzed by RIA for T4, and by IRMA for TSH as first-line tests. FT3 and TBG were requested as back-up tests when indicated. Patients were classified on the basis of these results and the clinical information received. All the samples were reanalyzed for FT4 and TSH on the Amerlite Processing Center, which is a batch, semiautomated immunoassay system. The thyroid status of the patients was compared using the two protocols and available clinical data.

There was good correlation between TSH-IRMA and TSH-30 in the 160 patients classified as euthyroid (r = 0.956; p < 0.001) and no euthyroid patient was reclassified with the new strategy. In 21 patients with borderline raised TSH-IRMA, FT4 was found to be low in only 2. All 11 patients classified as hypothyroid had TSH results greater than 10 mU/L and all except 2 patients had FT4 less than 11 nmol/L. The status of 21 hyperthyroid as well as 40 patients on carbimazole could be determined biochemically on the basis of agreement between both the FT4 and TSH-30 results. FT3 was only required if the FT4 and TSH-30 results were not in agreement. In 42 patients on T4 therapy, adequacy of replacement was assessed better using FT4 and TSH-30. No patient required backup testing with TBG to determine thyroid status using the new testing protocol. The change in TFT protocol reduced the 95% turn-around time from 3 days to 1 day.

The introduction of FT4 and TSH-30 as first-line TFT improved the turn-around time for TFT, resulted in 25% reduction in personnel requirements, 60% reduction in FT3 assays, and discontinuation of TBG assay.