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PubMed1989

Effects of illness on thyroid function tests.

Severe illness of any type predictably leads to abnormal results on thyroid function tests. The first apparent changes are a decrease in total triiodothyronine (T3) and an increase in reverse T3. As disease progresses, a marked decline in thyroxine and an increase in T3 resin uptake are observed. Thyrotropin levels remain normal, confirming that the patient is euthyroid despite marked alterations in thyroid function tests. Supplemental thyroid hormone has never been shown to be of any value, and may indeed be harmful, in euthyroid patients with abnormal thyroid function. Recognition of the euthyroid sick syndrome is vital to avoid needless therapy.

Euthyroid Sick Syndromes↗
PubMed1993

Interindividual differences in the pituitary-thyroid axis influence the interpretation of thyroid function tests.

OBJECTIVE: We investigated interindividual differences in the shape, slope and setpoint of the pituitary-thyroid axis (PTA) in normal persons. Based on these physiological data we propose a novel bivariate concept for the interpretation of thyroid function tests which is less biased by interindividual differences in the PTA than the currently used univariate approach. DESIGN: In two separate trials (A and B), healthy volunteers were given small, increasing doses of T3 (7.5-45 micrograms/day orally) over 5 days. The regulation characteristics of the individual PTAs and the effects of age and gender were assessed by general linear regression models. In addition, serum samples were collected from normal persons to establish the proposed bivariate approach for the interpretation of thyroid function tests. SUBJECTS: The regulatory characteristics of the PTA were determined in a total of 21 normal volunteers (eight females, 13 males; age 24-49 years). Single blood samples were collected from 257 normal volunteers. The participants had no history of pituitary or thyroid disease. MEASUREMENTS: Free and total thyroid hormone and TSH concentrations were determined in the serum. All samples from one person were analysed in the same assay in duplicate. RESULTS: A log-linear relationship between T3 and TSH was found to describe best the individual PTA (multiple r = 0.96). However, significant differences in the setpoint (P < 0.001) and to a lesser degree in the slope (P < or = 0.05) of the PTA were detected; this variability was not dependent on age or gender. Since these findings invalidate the assumptions on which the current univariate interpretation of thyroid function tests is based, we propose a novel model for the evaluation of thyroid function tests derived from the experimentally determined shape and average slope of the PTA. CONCLUSIONS: The presence of significant age and gender-independent interindividual variations in the setpoint of the pituitary-thyroid axis raises conceptual problems with the current approach for interpreting thyroid function tests. An easy to use graphical bivariate representation of the normal ranges for thyroid function tests is presented and exemplified by the thyroid hormone and TSH measurements in a large reference population. This concept should improve the diagnostic accuracy in the borderline-normal, and particularly subclinical hypothyroid region of these hormone measurements.

Adult↗
PubMed2001

Thyroid function testing in Greyhounds.

OBJECTIVE: To evaluate thyroid function in healthy Greyhounds, compared with healthy non-Greyhound pet dogs, and to establish appropriate reference range values for Greyhounds. ANIMALS: 98 clinically normal Greyhounds and 19 clinically normal non-Greyhounds. PROCEDURES: Greyhounds were in 2 groups as follows: those receiving testosterone for estrus suppression (T-group Greyhounds) and those not receiving estrus suppressive medication (NT-group Greyhounds). Serum thyroxine (T4) and free thyroxine (fT4) concentrations were determined before and after administration of thyroid-stimulating hormone (TSH) and thyroid-releasing hormone (TRH). Basal serum canine thyroid stimulating hormone (cTSH) concentrations were determined on available stored sera. RESULTS: Basal serum T4 and fT4 concentrations were significantly lower in Greyhounds than in non-Greyhounds. Serum T4 concentrations after TSH and TRH administration were significantly lower in Greyhounds than in non-Greyhounds. Serum fT4 concentrations after TSH and TRH administration were significantly lower in NT-group than T-group Greyhounds and non-Greyhounds. Mean cTSH concentrations were not different between Greyhounds and non-Greyhounds. CONCLUSIONS AND CLINICAL RELEVANCE: Previously established canine reference range values for basal serum T4 and fT4 may not be appropriate for use in Greyhounds. Greyhound-specific reference range values for basal serum T4 and fT4 concentrations should be applied when evaluating thyroid function in Greyhounds. Basal cTSH concentrations in Greyhounds are similar to non-Greyhound pet dogs.

Animals↗
PubMed1989

Thyroid function tests in ageing and their relation to associated nonthyroidal disease.

Thyroid function tests of 179 euthyroid geriatric inpatients (83 +/- 6 yr) unaffected by acute diseases or malnutrition were investigated and compared with those of 76 ambulatory healthy younger subjects (42 +/- 13 yr). Elderly population was divided in three groups, respectively: group G I (n = 37, 65-78 yr), group G II (n = 64, 79-85 yr) and group G III (n = 78, over 85 yr). Severity-of-illness index of the patients was evaluated at entry in the study protocol. While total thyroxine (TT4), free triiodothyronine (FT3) and TSH levels remained unchanged, circulating total triiodothyronine (TT3) was significantly lower (113 +/- 32 vs 150 +/- 31 ng/dl, p less than 0.05) and free thyroxine (FT4) was significantly higher (12.4 +/- 2.7 vs 10.3 +/- 2.3 pg/ml, p less than 0.05) in aged people. Furthermore, TT3 decreased significantly from 130 +/- 36 in G I to 110 +/- 33 in G II and to 108 +/- 25 in G III (p less than 0.01), and FT4 increased progressively although not significantly in the same groups. A close correlation was found between TT3 and severity index in male observations only (r = -0.43, p less than 0.01), as well as between FT4 and severity index in both sexes (r = 0.51, p less than 0.001 for men, r = 0.21, p less than 0.01 for women). These data suggest that thyroid function tests have to be cautiously interpreted in a geriatric population, particularly in relation to the severity of the clinical state, and reference values should be determined for TT3 and FT4 in the ageing process.

Age Factors↗
PubMed1998

Alternative sequences of thyrotropin and free thyroxine assays for routine thyroid function testing. Quality and cost.

BACKGROUND: Current guidelines and practices for thyroid function testing are strongly affected by the usually higher patient billing charges and Medicare reimbursement for thyrotropin (TSH) vs free thyroxine (FT4) tests, despite their comparable direct costs. OBJECTIVE: Due to recently reduced laboratory costs, to reexamine the effectiveness and cost of alternative test sequences. METHODS: Alternative test sequences involve using the TSH test first, followed, if the TSH test result is abnormal, by the FT4 test; the FT4 test first, followed by the TSH test; and doing both tests together. We applied these strategies to consecutive patients referred for any thyroid function test to a health maintenance organization, a multispecialty fee-for-service group, a military hospital, and a commercial laboratory. Effectiveness was determined from a literature review. The cost was determined from direct costs and the distribution of diagnostic categories. RESULTS: The TSH and FT4 tests have similar sensitivities for detecting clinical hyperthyroidism and hypothyroidism. The TSH test detects subclinical function, and it monitors thyroxine treatment better; the FT4 test detects central hypothyroidism, and it monitors rapidly changing function better. Direct costs for both were equal, but charges for the TSH test were higher. The average direct cost per patient, starting with the FT4 test, was $4.61; starting with the TSH test, $5.90; and starting with both tests together, $6.50. Medicare reimbursements correlated poorly with costs. CONCLUSIONS: Starting with the TSH test and reflexing to the FT4 test provides a better first-line all-purpose sequence than the reverse. In managed care settings, the slightly higher direct cost of this approach is offset by greater clinical effectiveness. In fee-for-service settings, cost differences can be nearly eliminated by equalizing TSH and FT4 charges to reflect current direct-cost realities. Obtaining both tests together overcomes the disadvantages of each at a slightly higher direct cost.

Humans↗
PubMed2003

Thyroid function testing in outpatients: are both sensitive thyrotropin (sTSH) and free thyroxine (FT4) necessary?

BACKGROUND AND OBJECTIVES: Despite improved thyroid function testing assays, appropriate use of these commonly ordered tests to detect thyroid dysfunction remains controversial. This study determined if a normal sensitive thyroid stimulating hormone (sTSH) test alone is sufficient to rule out thyroid dysfunction in outpatients. METHODS: This was a retrospective analysis of initial sTSH and free thyroxine index (FT4) tests ordered during a 26-month period. Test results were classified as concordant if both the sTSH and FT4 indicated the same findings (ie, euthyroid, hyperthyroid, or hypothyroid). The results were classified as discordant if the sTSH and FT4 did not indicate the same findings. RESULTS: There were 1,392 paired sTSH and FT4 results. Of 1,340 results classified as concordant (96.2%), 1,187 specimens were consistent with euthyroidism, 41 with hyperthyroidism, and 112 with hypothyroidism. Of the remaining 52 (3.8%) discordant results, 47 met the definition of subclinical thyroid dysfunction. Excluding these 47 results yielded a concordance rate of 99.6%. Of the 1,192 normal sTSH results, FT4 was low in two and high in three. If FT4 tests had not been ordered on the 1,192 specimens with normal sTSH levels, the savings over the study period would have been more than dollars 3,360. CONCLUSIONS: If the sTSH is normal, the likelihood of an abnormal FT4 is very small. sTSH alone is adequate to screen outpatients for thyroid dysfunction. Limiting FT4 tests to those with abnormal sTSH results will result in cost savings.

Cost Savings↗
PubMed2002

Results of thyroid function tests and concentrations of plasma proteins in dogs administered etodolac.

OBJECTIVE: To determine the effects of etodolac administration on results of thyroid function tests and concentrations of plasma proteins in clinically normal dogs. ANIMALS: 19 healthy random-source mixed-breed dogs. PROCEDURE: Blood samples for measurement of serum thyroxine (T4), 3,5,3'-triiodothyronine (T3), free T4 (fT4), and endogenous canine thyroid stimulating hormone (cTSH) were measured twice before as well as on days 14 and 28 of etodolac administration (mean dosage, 13.7 mg/kg, PO, q 24 h). Plasma total protein, albumin, and globulin concentrations and serum osmolality were measured once before as well as on days 14 and 28 of etodolac administration. RESULTS: Etodolac administration did not significantly affect serum T4, T3, fT4, or cTSH concentrations or serum osmolality. Significant decreases in plasma total protein, albumin, and globulin concentrations were detected on days 14 and 28 of administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results of thyroid function tests are not altered when etodolac is administered for up to 4 weeks. Therefore, interpretation of results of these tests should accurately reflect thyroid function during etodolac treatment. Plasma total protein, albumin, or globulin concentrations that are less than the respective reference range in a dog administered etodolac for > or = 2 weeks may be an effect of treatment rather than an unrelated disease process. A decrease in plasma protein concentrations may reflect subclinical injury of the gastrointestinal tract.

Animals↗
PubMed2001

Thyroid function tests, serum lipids and gender interrelations in a middle-aged population.

OBJECTIVE: To study the value of screening for thyroid function in a screening program for hyperlipidaemia. DESIGN: A screening study in primary health care. SETTING: All individuals in a defined rural area, Söderåkra, Sweden, aged 40-59 years were invited to a screening programme at the local primary health care centre. PARTICIPANTS: 782 individuals were invited for screening. Blood samples were obtained from 88% of the invited males and from 92% of the females. MAIN OUTCOME MEASURES: Thyroid function tests (thyroid stimulating hormone (TSH) and free T4), serum lipids (total-cholesterol, HDL-cholesterol, LDL-cholesterol and s-triglycerides), b-glucose and body anthropometry (body mass index and waist to hip circumference) were measured. RESULTS: 0.57% of males and 1.13% of females showed evidence of hypothyroidism as defined by a TSH value greater than 3.75 mU/l of those with s-cholesterol concentration above 7 mmol/l. In addition, higher TSH values in females were associated with higher s-cholesterol, s-LDL-cholesterol and s-triglycerides. CONCLUSION: It seems appropriate to screen for hypothyroidism in females with s-cholesterol above 7.0 mmol/l.

Adult↗
PubMed1992

Abnormal thyroid function test results in patients taking salsalate.

OBJECTIVE: To evaluate how the nonsteroidal anti-inflammatory agent salsalate affects the results of routine thyroid function tests. DESIGN: In a cohort of patients taking salsalate for various rheumatic conditions, thyroid function tests were performed with patients on and off the drug. SETTING: Primary care of ambulatory patients in a university medical center. PATIENTS: A convenience sample of 14 euthyroid subjects, none of whom was taking thyroid hormone or other medication recognized to alter thyroid function. INTERVENTION: Treatment with therapeutic doses of salsalate for a mean period of 44 weeks. MAIN OUTCOME MEASURES: Serum levels of thyroxine (T4), free T4, thyroid hormone binding ratio, free T4 index (the product of T4 and the thyroid hormone binding ratio), triiodothyronine, and thyrotropin. RESULTS: Serum T4 dropped from a mean baseline level of 96.7 nmol/L off salsalate to 53.4 nmol/L on it (P less than .001), and the free T4 index showed a parallel decline from 85.9 to 50.4 (P less than .001), with both values falling into the hypothyroid range. Similarly, free T4 levels and total triiodothyronine concentrations were low in several patients treated with salsalate. Serum thyrotropin levels declined transiently, falling from a mean of 3.2 to 1.7 mU/L (P less than .02) in patients treated for less than 3 weeks. Patients treated for longer periods had levels comparable to baseline. Despite these changes in the thyroid function test results, all subjects remained clinically euthyroid. CONCLUSION: Salsalate commonly produces abnormalities in routine thyroid function test results similar to those found in central hypothyroidism.

Adult↗
PubMed1980

A procedure for the redefinition of equivocal results in thyroid function tests.

A retrospective analysis has been made of patients who had been classified (on the basis of measurements of serum thyroxine and thyroid hormone uptake test) as equivocal thyrotoxic (273 patients) or as equivocal hypothyroid (352 patients). The final diagnosis of these patients has been traced from their medical records. The results illustrate that control groups of euthyroid, thyrotoxic, and primary hypothyroid subjects differ from these equivocal groups. The populations initially classified as equivocal have been used to redefine the combinations of values obtained in the serum thyroxine and thyroid hormone uptake test which must be classed as equivocal. Using this redefinition, it is shown that a number of additional tests had been carried out when it could now be predicted with confidence that no useful new information would be obtained. The procedure described is not limited to tests of thyroid function and could easily be applied in most laboratories to redefine the ranges of results classified as equivocal.

Adolescent↗
PubMed1977

The practical use of thyroid function tests.

The diagnosis of thyroid disorders can usually be established by two tests: the serum T4 and the resin T3 uptake (RT3U). The T4 test measures both free and bound thyroxine; the RT3U reflects the number of binding sites available on thyroid-binding globulin. The values of these two tests can be used to calculate a free thyroxine index (FTI), which gives an approximation of the free T4 in the serum. Measurement of thyroid-stimulating hormone (TSH) is useful for the diagnosis of hypothyroidism, while the thyrotropin-releasing hormone (TRH) test may facilitate diagnosis of hyperthyroidism.

Female↗
PubMed1978

Thyroid function tests in adults with Down's syndrome.

Thyroid status was studied in 24 patients above the age of 40 years with Down's syndrome. Three patients had thyroid function tests indicating hypothyroidism. Eight patients had thyroid autoantibodies in serum and 8 patients had a higher than normal level of thyroid stimulating hormone in serum. None of the patients had figures indicating thyrotoxicosis. None of the patients showed any of the clinical signs usually seen in patients with hypothyroidism. It is concluded that biochemical tests indicating hypothyroidism are much more often seen in patients with Down's syndrome than in normal subjects and that thyroid status should be assessed in old patients with this disease.

Adult↗