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Abnormal serum free thyroid hormone levels due to heparin administration
1Department of Medicine, University Hospital of Wales, Cardiff, UK. laji@doctors.org.uk
QJM : Monthly Journal of the Association of Physicians
|August 31, 2001
Summary
Heparin administration can falsely elevate free thyroid hormone levels, potentially due to free fatty acids interfering with hormone binding. This can cause diagnostic confusion, highlighting the need for physician awareness.
Area of Science:
- Clinical Chemistry
- Endocrinology
- Pharmacology
Background:
- Thyroid hormone levels are critical for diagnosing thyroid disorders.
- Accurate measurement of free thyroid hormones is essential for clinical decision-making.
- Heparin is a commonly used anticoagulant with potential laboratory interferences.
Observation:
- Four cases are presented where heparin administration led to artefactual elevations in measured free thyroid hormone concentrations.
- The observed abnormalities caused diagnostic confusion in patient management.
- The exact mechanism remains unclear but may involve free fatty acids displacing thyroid hormones from binding proteins.
Findings:
- Heparin, both fractionated and unfractionated, can interfere with the accurate measurement of free thyroid hormones.
- This interference results in artefactual increases in measured hormone levels.
- The phenomenon is poorly appreciated but clinically significant.
Implications:
- Physician awareness of heparin-induced abnormalities in thyroid hormone assays is crucial.
- Recognizing this interference can prevent misdiagnosis and unnecessary investigations.
- This understanding aids in improving the accuracy of thyroid function testing in patients receiving heparin.