Category: Thyroid

Monitor: 24

24 - AFFECT OF L-CARNITINE ON THYROID FUNCTION TESTS

Friday, Apr 26
11:00 AM – 11:30 AM

Objective : Review a rare case of L-carnitine affecting Thyoid function tests. L-Carnitine is a quaternary amine ubiquitous in biological tissues of mammals, where it plays an important role in energy metabolism. It facilitates long-chain fatty acid entry into mitochondria for oxidation and subsequent energy production. Usually takenas OTC supplements. Many of the OTC have been reported to affect the levels of thyroid function tests but only few cases have been reported with L-carnitine.


Methods :

We present the case of a 55-year-old Caucasian male who was admitted for Eosinophilic Pneumonitis and was found to have abnormal thyroid function tests.  He complained of fatigue, malaise, diarrhea and diaphoresis but no palpitation, heat intolerance, weight loss, insomnia, eye or neck symptoms. No known personal of family history of thyroid disease. Medication review was negative for thyroid medications and recent iodine contrast exposure. He reported taking Niacin and L-carnitine at home. He was afebrile, pulse was 94, BP 155/104. Physical examination was significant for tachycardia and inspiratory crackles, negative for tremors, proptosis, hyperreflexia and thyromegaly. Laboratory workup revealed TSH of <0.005 mc IU/ml, FT4of 2.02ng/dl, FT3 of 7.03pg/ml, Anti-microsomal Antibodies <28u/ml, (TSI) <15u/ml, WBCs 41.4 thou/mcl and eosinophil 65.6%.L-carnitine was discontinued, and thyroid function tests were repeated in 2 weeks and showed improvement. He was kept off of L-carnitine for 3 months and repeat testing showed normal levels of TSH with 3.63 mc IU/ml, Free T4 of 0.94ng/dl and Free T3 of 3.2pg/ml. It was concluded that suppressed TSH and elevated FT3 and FT4 were secondary to L-carnitine. 


Results : n/a


Discussion :

L-carnitine is a quaternary amine ubiquitous in mammalian tissues and key factor in energy production(1). IL-carnitine inhibits thyroid hormone entry into cell nuclei, indicating that it is a naturally occurring inhibitor of thyroid hormone.


Few cases reported showing L-carnitine was used as a treatment for hyperthyroidism. In one case, a man with hyroid storm treated withL-carnitine and methimazole(4). In other, a cancer patient treated with carnitine and  propranolol for hyperthyroidism (6). Our patient was clinically euthyroid and biochemically hyperthyroidism. The thyroid function tests got normalized after the discontinuation of L-carnitine.


Conclusion : This case confirms that L-carnitine does affect TFTS and reveals the importance of medications review before interpreting the thyroid function tests.  Prospective randomized controlled trials are needed to address clinicians to define the appropriate treatment-settings for hyperthyroidism with L-carnitine.

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Yusha Zakai

Endocrine Fellow
University of Tennessee Health sciences Center
Memphis, Tennessee

Internal medicine residency from Macneal Hospital, CHicago, IL in 2018. Current Fellow at University of Tennessee Health Sciences Center

Ebenezer Nyenwe

Faculty member
University of Tennessee Health sciences Center

Current faculty member at University of Tennessee Health Sciences center

Yusha Zakai

Endocrine Fellow
University of Tennessee Health sciences Center
Memphis, Tennessee

Internal medicine residency from Macneal Hospital, CHicago, IL in 2018. Current Fellow at University of Tennessee Health Sciences Center