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[The negative TRH test: new differential assessment using a sensitive TSH assay]
P Lind1, G Klima, P Költringer
1Krankenhaus der Barmherzigen Brüder Graz-Eggenberg, Interne Abteilung.
Schweizerische Medizinische Wochenschrift
|August 9, 1988
Summary
This study demonstrates that the IRMA technique for thyroid-stimulating hormone (TSH) measurement improves accuracy, aiding in the diagnosis of hyperthyroidism. A negative thyrotropin-releasing hormone (TRH) test requires further evaluation, as it doesn't always indicate hyperthyroidism.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Thyroidology
Background:
- The accurate assessment of thyroid function is crucial for diagnosing and managing thyroid disorders.
- Traditional TSH assays have limitations in sensitivity and accuracy, potentially leading to misdiagnosis.
- The thyrotropin-releasing hormone (TRH) test is used to evaluate thyroid status, but interpretation of a negative result can be complex.
Purpose of the Study:
- To evaluate the diagnostic utility of an improved TSH assay (IRMA principle) in assessing thyroid function.
- To re-evaluate the significance of a negative TRH test in a large cohort of thyroid inpatients.
- To differentiate between euthyroid, hyperthyroid, and borderline states using basal and stimulated TSH levels.
Main Methods:
- Utilized the immunoradiometric assay (IRMA) technique for TSH determination, offering enhanced sensitivity and accuracy.
- Analyzed basal TSH (bTSH) and stimulated TSH (sTSH) values from 355 thyroid inpatients with blunted TSH response.
- Correlated TSH assay results with clinical assessments to exclude hyperthyroidism.
Main Results:
- The IRMA technique achieved lower detection limits (0.1 mU TSH/l) and higher accuracy compared to TSH RIA.
- In overt hyperthyroidism, basal TSH was <0.1 mU/l (95%) and stimulated TSH was <0.5 mU/l (100%).
- Among clinically euthyroid patients, 78% showed blunted basal TSH (0.1-0.4 mU/l) with a significant increase in stimulated TSH (0.5-2.5 mU/l).
- In patients with sTSH between 0.5-2.5 mU/l (excluding L-thyroxine treated), 66% were euthyroid and 34% borderline, with no hyperthyroid cases.
Conclusions:
- The improved TSH assay (IRMA) enhances the accuracy of thyroid function assessment.
- A negative TRH test (sTSH <2.5 mU/l) requires careful interpretation, as it can be observed in euthyroid and borderline states.
- The study provides a clearer differential diagnosis for patients with blunted TSH response, improving hyperthyroidism exclusion.