Clinical Evaluatin of Accuracy in Determining Serum Free Thyroxine and Free Triiodothyronine in Patients with Non-thyroidal Illness: Immunoglobulin Effect on T3/TBG Ratio and T4/TBG Ratio.

Abstract A novel interference with measurements of serum free thyroxine (FT4) caused by rheumatoid factor (RhF) is described. We found misleading, sometimes gross, increases of FT4 results in 5 clinically euthyroid elderly female patients with high RhF concentrations. All 5 patients had high FT4 on Abbott AxSYM® or IMx® analyzers. “NETRIA” immunoassays gave misleading results in 4 of the 5 patients; Amerlex-MAB® in 2 of 4 patients; AutoDELFIA®in 2 of the 5; and Corning ACS-180® and Bayer Diagnostics Immuno 1® in 1 of the 5. BM-ES700® system results for FT4 in these women remained within the reference range. Results for serum T4, thyroid-stimulating hormone, free triiodothyronine, thyroid-hormone-binding globulin, and FT4 measured by equilibrium dialysis were normal in all 5 patients. Drugs, albumin-binding variants, and anti-thyroid-hormone antibodies were excluded as interferences. Addition to normal serum of the RhF isolated from each of the 5 patients increased the apparent FT4 (Abbott AxSYM). Screening of 83 unselected patients demonstrated a highly significant positive correlation between FT4 (Abbott AxSYM) and RhF concentrations. Discrepant, apparently increased FT4 with a normal result for thyroid-stimulating hormone should lead to measurement of the patient’s RhF concentration.

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Circadian thyrotropin variations are preserved in normal pregnant women

Acta Endocrinologica ◽

10.1530/eje.0.1330071 ◽

1995 ◽

Vol 133 (1) ◽

pp. 71-74 ◽

Cited By ~ 6

Author(s):

Elio Roti ◽

Luigi Bartalena ◽

Roberta Minelli ◽

Mario Salvi ◽

Eliana Gardini ◽

...

Keyword(s):

Circadian Rhythm ◽

Pregnant Women ◽

Free Thyroxine ◽

Third Trimester ◽

Circadian Variations ◽

Free Triiodothyronine ◽

Serum Free ◽

Trimester Pregnancy ◽

Serum Tsh ◽

Serum Free Thyroxine

Roti E, Bartalena L, Minelli R, Salvi M, Gardini E, Pistolesi A, Martino E, Braverman LE. Circadian thyrotropin variations are preserved in normal pregnant women. Eur J Endocrinol 1995;133:71–4. ISSN 0804–4643 Serum thyrotropin (TSH) concentration circadian rhythm is abolished in many endocrine and nonendocrine diseases. In the present study we have measured serum TSH concentration over 24 h every 2 h in second and third trimester pregnant women. During the 24-h period, serum free thyroxine and free triiodothyronine concentrations did not change significantly. In contrast, serum TSH concentrations demonstrated significant circadian variations both in the second and third trimester pregnant women (p<0.02 and p <0.005, respectively). In summary, second and third trimester pregnancy is associated with a normal circadian TSH rhythm. Elio Roti, Centro per lo Studio, Prevenzione, Diagnosi e Cura delle Tireopatie, University of Parma, via Gramsci 14, 1-43100 Parma, Italy

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Serum free thyroxine and free triiodothyronine concentrations in pregnancy.

BMJ ◽

10.1136/bmj.287.6389.394 ◽

1983 ◽

Vol 287 (6389) ◽

pp. 394-394 ◽

Cited By ~ 23

Author(s):

J A Franklyn ◽

M C Sheppard ◽

D B Ramsden

Keyword(s):

Free Thyroxine ◽

Free Triiodothyronine ◽

Serum Free ◽

In Pregnancy ◽

Serum Free Thyroxine

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Levothyroxine therapy and serum free thyroxine and free triiodothyronine concentrations

Journal of Endocrinological Investigation ◽

10.1007/bf03343972 ◽

2002 ◽

Vol 25 (2) ◽

pp. 106-109 ◽

Cited By ~ 38

Author(s):

Kenneth A. Woeber

Keyword(s):

Free Thyroxine ◽

Free Triiodothyronine ◽

Serum Free ◽

Serum Free Thyroxine

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Serum free thyroxine in patients with T3-toxicosis

Acta Endocrinologica ◽

10.1530/acta.0.1100354 ◽

1985 ◽

Vol 110 (3) ◽

pp. 354-359 ◽

Cited By ~ 10

Author(s):

Enio Martino ◽

Alessandro Pacchiarotti ◽

Fabrizio Aghini-Lombardi ◽

Lucia Grasso ◽

Giovanni Bambini ◽

...

Keyword(s):

Clinical Evidence ◽

Elevated Serum ◽

Normal Serum ◽

Free Thyroxine ◽

Total Serum ◽

Free Triiodothyronine ◽

Serum Free ◽

Serum Thyroxine ◽

Free Thyroxine Index ◽

Serum Free Thyroxine

Abstract. The serum free thyroxine concentration was measured by direct radioimmunoassay in 38 untreated T3-thyrotoxic patients with elevated serum total and free triiodothyronine, normal serum thyroxine and free thyroxine index, no TSH response to TRH, and with clinical evidence of hyperthyroidism. An elevation of circulating free thyroxine values was observed in 58% of the patients, whereas total serum thyroxine concentration was within the normal range. It is suggested, therefore, that T3-thyrotoxicosis should be reserved for patients with elevated serum total T3 and free T3 concentrations and normal serum total T4 and free T4 concentrations. Serum thyroxine-binding globulin concentrations were significantly lower (P < 0.025) in patients with an elevated serum free thyroxine (18.7 ± 3.6 μg/ml: mean ± sd) as compared with those in patients with a normal free thyroxine concentration (23.4 ± 2.6 μg/ml). In addition, no daily fluctuations in total and free thyroxine concentration were observed in 6 patients over a 4–8 day period.

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Effects of Age and Health on the Euthyroid Reference Ranges for Serum Free Thyroxine and Free Triiodothyronine

Nuklearmedizin ◽

10.1055/s-0038-1624280 ◽

1985 ◽

Vol 24 (02) ◽

pp. 57-65 ◽

Cited By ~ 6

Author(s):

J. E. M. Midgley ◽

K. R. Gruner

Keyword(s):

Lower Limit ◽

Healthy Subjects ◽

Thyroid Dysfunction ◽

Reference Range ◽

Free Thyroxine ◽

Reference Ranges ◽

Free Triiodothyronine ◽

Serum Free ◽

Young Subjects ◽

Age Range

SummaryAge-related trends in serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations were measured in 7248 euthyroid subjects (age-range 3 months to 106 years). 5700 were patients referred to hospitals for investigation of suspected thyroid dysfunction, but who were diagnosed euthyroid. 1548 were healthy blood donors (age-range 18-63 years) with no indication of thyroid dysfunction. FT4 concentrations were little affected by the age, the sex or the state of health of the subjects in either group. Serum FT3 concentrations were significantly affected by both age and health factors. The upper limit of the euthyroid reference range for young subjects up to 15 years was about 20% higher (10.4 pmol/1) than for adult subjects older than 25 years (8.8 pmol/1). The change in the upper limits typical of young subjects to that typical of adults occurred steadily over the decade 15–25 years. After this age, little further change occurred, especially in healthy subjects. Additionally, the lower limit of the euthyroid range for FT3 was extended by the inclusion in the reference group of patients referred to hospitals. Compared with the lower limit of the FT3 range for healthy subjects (5 pmol/1), the corresponding limit for referred subjects (young or adult) was 3.5–3.8 pmol/1. Broadening of the FT3 reference range was probably brought about by a significant number of patients in the hospital-referred group with the “1OW-T3 syndrome” of mild non-thyroidal illness. Accordingly, FT3 was inferior to FT4 in the discrimination of hypothyroidism, as FT4 was unaffected by this phenomenon. Effects of age and non-thyroidal illness on serum FT3 concentrations require great care when selecting subjects for a laboratory euthyroid reference range typical of the routine workload. Constraints on the choice of subjects for FT4 reference ranges are less stringent.

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