Forty-one routine TSH assays were carried out by applying newly developed, highly sensitive TSH RIA (T. Mori, et al., Folia Endocrinol. Jap., 56 : 1231, 1980).
B/B
0 percent of the least standard point (0.156μU/ml) was consistently lower than B
0 and higher than that of 0.31μU/ml.
The distributions of assayed TSH concentrations in 1394 sera revealed that 34.8% of the total were in an undetectable range when measured by conventional method ( < 1.0μU/ml), but this method picked up 16.4% (0.156-1.0μU/ml), and only 5.4% exceeded the upper limit (20μU/ml).
TRH test results (500μg i.v. bolus) in 45 cases of thyroid disorders with low or normal basal TSH revealed that the peak TSH of those with basal TSH of 0.156-1.0μU/ml (8.98 ± 4.15μU/ml) was significantly different from those of less than 0.156μU/ml or 1.0-3.2μU/ml.
Further, TSH concentrations in 19 patients after T3 administration (75μg × 7 days) were 0.183 ± 0.073μU/ml, and all but one (0.43μU/ml) showed values lower than the normal range (0.31-3.2μU/ml).
Thyroid hormone concentrations in cases with TSH of 0.156-1.0μU/ml were limited in the ranges of less than 300 ng/dl T3 and/or less than 15μg/dl T4, and these were considered to be the threshold of definite TSH inhibition. TSH concentrations of less than 0.31μU/ml were generally associated with clinical conditions or laboratory findings of decreased TSH secretion, although there were a few cases showing undetectable TSH with normal or low T4 and T3.
In conclusion, this highly sensitive TSH RIA could detect 76.2% of serum TSH in various thyroid states, and detection of a lower TSH range was found quite meaningful. Routine application of this assay should be strongly recommended.
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