Use of the Free Thyroxine Index to Refine the Lower Limit of a Free Thyroxine Immunoassay for Detection of Secondary Hypothyroidism
| Autor: | James V. Hennessey, Gregory P. Westcott, Christopher M. Mulla |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
medicine.medical_specialty
Pituitary disease Endocrinology Diabetes and Metabolism Urology Thyrotropin 030209 endocrinology & metabolism Hypopituitarism Thyroid Function Tests Lower limit 03 medical and health sciences 0302 clinical medicine Endocrinology Hypothyroidism Thyroid-stimulating hormone Humans Medicine 030212 general & internal medicine Retrospective Studies Immunoassay medicine.diagnostic_test Receiver operating characteristic business.industry Magnetic resonance imaging General Medicine medicine.disease Thyroxine Triiodothyronine business hormones hormone substitutes and hormone antagonists Hormone |
| Zdroj: | Endocrine Practice. 27:8-14 |
| ISSN: | 1530-891X |
| DOI: | 10.4158/ep-2020-0210 |
| Popis: | Objective To determine the utility of measuring free T4 index (FT4I) in patients with low free T4 (FT4) levels using immunoassay and normal thyroid-stimulating hormone for the evaluation of secondary hypothyroidism. Methods We performed a retrospective medical chart review of patients seen at a single institution as outpatients who had a simultaneously normal thyroid-stimulating hormone level, low FT4 level, and any FT4I measured between June 2014 and October 2016. Demographic, laboratory, and imaging data were collected. Using FT4I as the reference for diagnosis of hypothyroidism, the sensitivity and specificity of the FT4 immunoassay’s lower-limit thresholds were determined. Within each threshold group, available brain imaging and biochemical evaluation were categorized according to the presence or absence of pituitary disease. Results A total of 155 sets of result pairs (FT4 and FT4I) performed on 118 subjects were analyzed. The lower limit of a normal FT4 level by immunoassay at this institution was 0.93 ng/dL, though all pairs with FT4 ≥0.89 ng/dL had a normal FT4I. All pairs with FT4 ≤0.67 ng/dL had a low FT4I. No pituitary macroadenomas were identified in any subject, though the rates of pituitary imaging in this patient sample were low. Conclusion Patients with a borderline low FT4 level by immunoassay often have normal FT4I. In such patients at our center, significant structural and biochemical pituitary pathology was uncommon. |
| Databáze: | OpenAIRE |
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