Medications that distort in vitro tests of thyroid function, with particular reference to estimates of serum free thyroxine

Pharmacological interference on L-thyroxine (L-T4) therapy can be exerted at several levels, namely from the hypothalamus/pituitary through the intestine, where the absorption of exogenous L-T4 takes place. A number of medications interfere with L-T4 therapy, some of them also being the cause of hypothyroidism. The clinician should be aware that some medications simply affect thyroid function tests with no need of modifying the dose of L-T4 that the patient was taking prior to their prescription. Usually, the topic of pharmacological interference on L-T4 therapy addresses the patient with primary hypothyroidism, in whom periodic measurement of serum thyrotropin (TSH) is the biochemical target. However, this minireview also addresses the patient with central hypothyroidism, in whom the biochemical target is serum free thyroxine (FT4). This minireview also addresses two additional topics. One is the costs associated with frequent monitoring of the biochemical target when L-T4 is taken simultaneously with the interfering drug. The second topic is the issue of metabolic/cardiovascular complications associated with undertreated hypothyroidism.

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Serum free thyroxine concentrations measured by chemiluminescence in hyperthyroid and euthyroid cats

Journal of the American Animal Hospital Association ◽

10.5326/15473317-32-6-489 ◽

1996 ◽

Vol 32 (6) ◽

pp. 489-494 ◽

Cited By ~ 6

Author(s):

M Paradis ◽

N Page

Keyword(s):

Thyroid Function ◽

Reference Values ◽

Free Thyroxine ◽

Radioactive Materials ◽

Serum Free ◽

Clinically Normal ◽

Serum Free Thyroxine

Serum free thyroxine (FT4) concentrations using chemiluminescence were measured in hyperthyroid cats (n = 72) and clinically normal cats (n = 129) to establish reference values and to determine if this method could be a useful alternative to total T4 (TT4) measurement by radioimmunoassay (RIA). Mean serum FT4 concentration (68.3 +/- 26.8 pmol/L) of hyperthyroid cats was significantly higher than that of euthyroid cats (22.9 +/- 4.8 pmol/L). Reference values for basal FT4 of hyperthyroid and healthy cats were 33 to 114 pmol/L and 16 to 30 pmol/L, respectively. The results of the present study suggest that FT4 measured by chemiluminescence could be a useful alternative to TT4 measured by RIA when evaluating thyroid function in cats, since the hazardous effects of radioactive materials on the manipulators and the environment could be avoided. Further studies are required to corroborate these preliminary findings.

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A Case Series of Patients With Central Hypothyroidism From Oxcarbazepine Therapy

Journal of Child Neurology ◽

10.1177/0883073820962926 ◽

2020 ◽

pp. 088307382096292 ◽

Cited By ~ 1

Author(s):

Bahareh Michelle Schweiger ◽

Aaron-James Lao ◽

Jane Tavyev

Keyword(s):

Thyroid Function ◽

Pediatric Population ◽

Case Series ◽

Metabolic Enzymes ◽

Thyroid Stimulating Hormone ◽

Free Thyroxine ◽

Central Hypothyroidism ◽

Serum Free ◽

Serum Free Thyroxine ◽

Stimulating Hormone

Many medications can impact thyroid function. Antiseizure medications have been shown to disrupt thyroid function in adults, but information is limited about how antiseizure medications may affect thyroid function in children. Oxcarbazepine is an analog of carbamazepine designed to minimize effects from the hepatic P450 metabolic enzymes. We have found that in the pediatric population, serum free thyroxine is reduced and thyroid-stimulating hormone concentrations are unchanged in patients taking oxcarbazepine with the mechanism thus being central hypothyroidism.

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INCREASE OF SERUM FREE THYROXINE FOLLOWING THE ADMINISTRATION OF THIOCYANATE AND OTHER ANIONS IN VIVO AND IN VITRO

Acta Endocrinologica ◽

10.1530/acta.0.0750707 ◽

1974 ◽

Vol 75 (4) ◽

pp. 707-716 ◽

Cited By ~ 10

Author(s):

N. Michajlovskij ◽

P. Langer

Keyword(s):

Time Course ◽

Linear Increase ◽

Free Thyroxine ◽

Peroral Administration ◽

Rat Serum ◽

Serum Free ◽

Serum Free Thyroxine

ABSTRACT Following the addition of thiocyanate (SCN−) to human and rat serum of 80 mg SCN−/ 100 ml (initial concentration before dialysis) a marked increase in serum free thyroxine (FT4) was found. The addition of equivalent doses of other antihyroid anions or permanganate showed a similar increase of FT4 in the order: BF4− < CIO4− = SCN− < MnO4−. The increase in the rat serum was greater than that in human serum. After peroral administration of these anions to the rats in amounts equal to 30 mg SCN−/rat the increase of FT4 was still higher. The addition of increased doses of SCN− to the human and rat sera (5-80 and up to 1600 mg SCN−/100 ml) caused a linear increase of FT4. Similarly, after the administration of various doses of SCN− to rats (5-30 mg SCN−/rat) a linear dose-response of the FT4 level in serum was observed. The time-course of the increase of % FT4 and absolute FT4 (AFT4) level after a single administration of SCN− to rats coincided with the increase of the serum SCN− level. However, after the disappearance of SCN− from the serum the % FT4 returned to the initial value, while the AFT4 was decreased. The effect of these anions probably consists in the competitive displacement of thyroxine from serum thyroxine-binding proteins. These and previous results suggested that thiocynate influences the plasma protein-thyroxine equilibrium and the possible role of an increased free thyroxine level on the action of thyroxine on various tissues and the hypothalamo-pituitary-thyroid feed-back is discussed.

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