ALTERNATIVE SEQUENCES OF THYROTROPIN AND FREE-THYROXINE ASSAYS FOR ROUTINE THYROID-FUNCTION TESTING - QUALITY AND COST

Background: Current guidelines and practices far thyroid function test ing are strongly: affected by the usually higher patient billing charg es and Medicare reimbursement for thyrotropin (TSH) vs free thyroxine (FT) tests, despite their comparable direct costs. Objective Due to re cently reduced laboratory costs, to reexamine the effectiveness and co st of alternative test sequences. Methods: Alternative test sequences involve using the TSH test first, followed, ii the TSI test result is abnormal, by the FT4 test; the FT4 test first, followed by the TSH tes t; and doing both tests together. We applied these strategies to conse cutive patients referred for any thyroid function test to a health mai ntenance organization, a multispecialty fee-for-service group, a milit ary hospital, and a commercial laboratory. Effectiveness was determine d from a literature review. The cost was deteremined from direct: cost s and the distribution of diagnostic categories. Result The TSH and FT 4 tests have similar sensitivities for detecting clinical hyperthyroid ism and hypothyroidism. The TSH test detects subclinical function, and it monitors thyroxine treatment better; the FT4 test detects central hypothyroidism, and it monitors rapidly changed function better. Direc t costs for both were equal, but charges for the TSH test were higher. The average direct cost per patient, starting with the FT4 test, was &4.61; starting with the TSH test, &5.90; and starting with both tests together, &6.50. Medicare reimbursements correlated poorly with casts . Conclusions: Starting with the TSH test and reflexing to the FT4 tes t provides a better first-line all-purpose sequence than the reverse. In managed care settings, the slightly higher direct cost of this appr oach is offset by greater clinical effectiveness. In fee-for-service s ettings, cost differences can be nearly eliminated by equalizing TSH a nd FT4 charges to reflect current direct-cost realities. Obtaining bot h tests together overcomes the disadvantages of each at a slightly hig her direct cost.