Summary
Objective, design and methods: Although TRH testing has been eliminated in the diagnosis of most benign thyroid
diseases, it is still controversial whether or not it can be replaced by ultrasensitive
determination of basal TSH for monitoring optimal TSH suppression in thyroid cancer
patients. We compared basal and TRH-stimulated TSH values measured by a 2nd generation assay (lower detection limit 0.1 mU/l) and by a 3rd generation assay (lower detection limit 0.005 mU/l) in 209 thyroidectomized thyroid
cancer patients under suppressive levothyroxine treatment. Results: In the 2nd generation assay all patients had basal TSH values < 0.1 mU/l (criterion of admission
in the study), and the TRH-stimulated TSH values were above the lower detection limit
in 47% of the patients (range < 0.1-1.0 mU/l). In the 3rd generation assay TSH was above the lower detection limit in 67% under basal conditions
(range < 0.005-0.098 mU/l), and in 83% after TRH stimulation (range < 0.005-1.000
mU/l). We observed close correlations (p < 0.001) between basal and TRH-stimulated
TSH in the 3rd generation assay (r = 0.86), between TRH-stimulated TSH in the 2nd and 3rd generation assay (r = 0.95), and between TRH-stimulated TSH in the 2nd generation assay and basal TSH in the 3rd generation assay (r = 0.73). The ratio between TRH-stimulated and basal TSH values
was in the average range 7-9 : 1. Subdividing the patients in three subgroups based
on the TRH-stimulated TSH values from the 2nd generation assay, the corresponding basal TSH values (median and [25.-75. percentile])
from the 3rd generation assay were < 0.005 [< 0.005-0.010] mU/l in subgroup A (2nd generation stim. TSH: < 0.15 mU/l), 0.032 [0.021-0.040] mU/l in subgroup B (2nd generation stim. TSH: 0.15-0.4 mU/l), and 0.066 [0.046-0.085] mU/l in subgroup C
(2nd generation stim. TSH: ≥ 0.5 mU/l). Conclusions: Even in those thyroid cancer patients where a high degree of TSH suppression is the
therapeutic goal, 3rd generation TSH assays enable a reliable adjustment of the levothyroxine dose by basal
TSH determinations. In laboratories still using 2nd generation assays, the monitoring of maximal TSH suppression in patients with high-risk
thyroid cancer should be performed by TRH testing.
Key words:
Thyroid cancer - TSH suppression - TRH testing - ultrasensitive TSH - third generation
assay
5. References
rainer.goerges@uni-essen.de
