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Reverse T3 does not reliably differentiate hypothyroid sick syndrome from euthyroid sick syndrome
1Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.
Thyroid : Official Journal of the American Thyroid Association
|December 1, 1995
Summary
Reverse T3 (RT3) is not a reliable marker for differentiating between hypothyroidism and euthyroidism in sick patients. Illness and certain medications can affect RT3 levels, leading to misinterpretation of thyroid function.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Thyroidology
Background:
- Assessing thyroid function in critically ill patients is challenging.
- Reverse T3 (RT3) has been proposed as a marker to differentiate between hypothyroidism and euthyroidism in non-thyroidal illness.
Observation:
- A retrospective analysis of 262 RT3 determinations in 246 patients was conducted.
- RT3 levels showed an inverse linear relationship with TSH (thyroid-stimulating hormone).
- RT3 levels were linearly related to bilirubin levels.
Findings:
- Patients with hypothyroidism and illness can have normal RT3 levels.
- Euthyroid patients can exhibit low RT3 levels.
- RT3 is unreliable for distinguishing between hypothyroid and euthyroid sick patients due to drug and disease effects on thyroid hormone metabolism.
Implications:
- Sixty percent of RT3 tests were ordered for questionable indications.
- Low or unmeasurable RT3 in conjunction with low free T4 did not consistently lead to thyroid hormone treatment.
- Clinical decisions regarding thyroid hormone replacement should not solely rely on RT3 levels in sick patients.