The thyrotropin-releasing hormone stimulation test: A methodological study

Abstract

Repeated thyroid-stimulating hormone (TSH) determinations were carried out for 90 or 180 minutes following thyrotropin releasing hormone (TRH) stimulation in 160 euthyroid psychiatric patients, most of whom had a symptomatic affective disorder. The purpose was to determine which of the simple TSH measurements from the TRH stimulation test (TRH-ST) yield(s) the most accurate index of pituitary TSH reserves and to clarify the relationship between the various TRH-ST methods reported in the literature. The area beneath the 180 minute TSH response curve, the best available parameter of pituitary TSH stores, was calculated and compared to simple indices of absolute TSH level and increase from 0 minute baseline. Fourteen parameters of the TSH response were determined; TSH 0, TSH 15, TSH 30, and TSH 45 represent the absolute levels at 0, 15, 30, and 45 minutes after TRH administration, respectively. TSH Max is the maximum TSH level attained after TRH infusion among all TSH measures. Δ TSH measures are the increase in TSH relative to baseline. The Δ Max TSH and Δ TSH 30 were highly correlated with the ideal index of pituitary TSH reserve (0 – 180 minute area). Subjects were classified as either blunted or normal over a broad range of Δ Max TSH criteria or thresholds. The number of misclassified subjects (false positives) at each criterion was counted for each of the seven possible combinations of Δ TSH 15, Δ TSH 30, and/or Δ TSH 45. The simplest index which produced the smallest number of false positives was Δ TSH 30 whereas Δ Max TSH (15, 30, and 45) produced no false positives. Overall, Δ TSH 30 was a very good simple index of pituitary TSH stores. This may be the preferred index when economy of time, expense, or blood samples is desired. However, it results in 5–7% false positives, which will compromise specificity somewhat. The preferred simple index of pituitary TSH reserves when accuracy is of highest priority is Δ Max TSH (15, 30, and 45). These data reveal that the TRH-ST can be simplified to include only four TSH levels: TSH 0, TSH 15, TSH 30, and TSH 45.