Total triiodothyronine

Sample material Serum or plasma (EDTA, oxalate or heparin). Citrate produces lower recovery rates. Serum or plasma can be stored in the refrigerator for one week at -i-4°C to -1-8 C. 

Specificity The antiserum is specific for triiodothyronine and shows low cross reactivity to naturally occurring substances or drugs that can occur in patient samples. 

Interferences No relevant influence exercised by haemolytic (haemoglobin up to 5 g/1), lipaemic (triglycerides up to 3 000 mg/dl) and icteric (bilirubin up to 20 mg/dl) samples. At protein concentrations 100 g/1 the T3 values measured can be lower by approximately 14% at protein concentrations 45 g/1 the values can be higher by about 20%. 

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Estrogen may increase hepatic production of thyroxine-binding globulin (TBG) and decrease TBG clearance, thus increasing serum total thyroxine (tT4) and, to a lesser extent, total triiodothyronine (tT3). As a result, increased tT4 and tT3 are seen in states of excessive estrogen and/or progestin, such as... 

W. Groskopf, B. Green, L. Sohn, and S. Hsu, Furosemide as a displacing agent in assay of total triiodothyronine, Clin. Chem. 37, 587-588 (1991). 

Plasma cortisol concentration is increased because of decreased metabolic clearance. The plasma concentrations of total triiodothyronine T3), thyroxine (T4), and TSH are considerably reduced, with the thyroxine concentration being most affected. This is partly due to reduced concentrations of thyroxine-binding globulin and prealbumin. 

Plasma growth hormone concentration may rise by as much as 15 times at the start of a fast but may return to normal after 3 days. Reduced energy expenditure is associated with decreased concentrations of thyroid hormones. Free and total triiodothyronine decrease by up to 50% witliin 3 days of the start of a fast. Free thyroxine concentration is also affected, but to a lesser extent total thyroxine is little changed. Urinary free cortisol is decreased by fasting, and the plasma cortisol concentration (free and total) shows a slight increase together with loss of the normal diurnal variation. 

Comeau L, Pianan U, Leo-Mensah T, Huntress MA, Hudson T. An automated chemiluminescent immunoassay test for total triiodothyronine. Clin Chem 1991 37 941. 

Datta P, Sundarapandyan K, Becker D. An automated chemiluminescent assay for total triiodothyronine (TT3) on tire Immulite. Cfin Chem 1991 37 1021. 

Kozwich D, Davis G, Sockol C. Development of a total triiodothyronine enzyme immunoassay in microtiter format. Chn Chem 1991 37 1040. 

PapanastasioU-Diamandi A, Khosravi M. Total triiodothyronine (Tj) measurement in serum by time-resolved fluorescence immunoassay. Clin Chem 1991 37 1029. 

After treatment is initiated, patients should be examined and thyroid function tests (serum-free thyroxine index and total triiodothyronine concentrations) measured every 2 to 4 months. Once euthyroidism is established, follow-up every 4 to 6 months is reasonable. 

Table 20.4 Concentrations of total thyroxine (tl4) and total triiodothyronine (tTs) in the blood sera of the dams and in the pooled sera of their pups, depending on the level of bromide intake in the dams...

We and others have reported a series of studies in ammonium perchlorate production workers who are exposed intermittently to perchlorate, resulting in urine perchlorate values of up to 40 mg daily, and in normal volunteers given 3—3 5 mg perchlorate daily for 2 weeks or 0.5 and 3mg daily for 6 months (Lawrence et al, 2000, 2001 Greer et al., 2002 Gibbs et al., 1998 Braverman et al, 2005, 2006). Thyroid function studies, including serum TSH, thyroxine (T4), free T4, and total triiodothyronine (T3), were not affected by perchlorate exposure in the plant or perchlorate administration to normal volunteers, despite a decrease in the thyroid uptake of at the higher exposures. Despite a mean exposure of 3 years to high levels of perchlorate in the production workers, no abnormalities of the thyroid evaluated by ultrasound were detected compared to a nonexposed local population (Braverman etal., 2005). 

Fig. 4. Results of total triiodothyronine assays (nanograms per 100 ml) in 60 normal subjects, 34 untreated thyrotoxic patients, 28 untreated patients with iodio-pathic myxedema, and 16 normal subjects on oral contraceptives (O.C.). The li t horizontal line in each panel represents the mean value for the group. Unpublished data of A. S. Kanagasabapathy and M. L. Wellby (1974).

Details of the analytical techniques used to estimate serum total thyroxine (TT4), total triiodothyronine (TT3) and thyroid stimulating hormone (TSH), and the means employed to check the effects of climatic conditions on sera have been reported previously ... 

Serum total triiodothyronine (TT ) was measured by radioimmunoassay with a normal range during pregnancy of 850-1750 pg/ml. 

Muscle heat production rate (P) and thyroid hormones concentrations in haemodialysis patients. TT4 = total thyroxine, TT3 = total triiodothyronine. Source reference 112. 

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