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

Rapid and reversible alterations in thyroid function tests in dehydrated patients

Dehydration commonly leads to hypovolemia and hemoconcentration. Changes in thyroid hormone-binding proteins secondary to hemoconcentration profoundly affect total serum thyroid hormone concentrations. The authors sought to determine the acute effects of mild to moderate dehydration on thyroid hormone levels/thyroid function tests and its reversibility upon rehydration. Total thyroxine, total triiodothyronine, free thyroxine, and the free-thyroxine index decreased significantly after hydration, in parallel with the decrease in extra cellular fluid volume status markers. Triiodothyronine-resin uptake increased after hydration. Thyrotropin levels decreased by 8% after hydration. Hypovolemia leads to simultaneous alterations in extracellular fluid volume markers and thyroid hormone serum concentrations that reverse rapidly upon rehydration. This constitutes, by itself, a distinct and new clinical entity.

Correlates of non-thyroidal illness syndrome in chronic obstructive pulmonary disease

Non-thyroidal illness syndrome (NTIS) is frequently detected in chronic, systemic diseases. The objectives of the current study is to assess the alterations of thyroid hormones during exacerbation period, recovery of exacerbation and stable phase of chronic obstructive pulmonary disease (COPD) and correlates of these hormonal alterations. A total of 83 stable COPD patients, 20 patients with acute exacerbation and 30 control subjects were evaluated. TT3, fT3, TT3/TT4 levels of both stable and exacerbation COPD groups were lower than control subjects. TSH was also decreased during exacerbation period. In follow-up of COPD exacerbation group, TSH, TT3, fT3 and TT3/TT4 were found to be increased in measurements on the day of discharge from hospital and after 1 month, compared to baseline values. TT3 and TT3/TT4 were lower in severe COPD; whereas TSH, fT3, TT3 and TT3/TT4 were lower in patients with severe hypoxemia. IL-6 and TNF-alpha were higher in both stable and exacerbation phase COPD groups and IL-6 was correlated to TT3 in stable COPD. As a result, there are significant alterations in thyroid hormones of stable COPD patients, which are related to severity of disease and hypoxemia. The hormonal changes are more significant during exacerbation and partially regress after 1 month when the disease is stabilized. We conclude that COPD patients should not be evaluated for thyroid disease during exacerbation of the disease, and thyroid function alterations during stable phase of the disease should be considered cautiously, since thyroid function abnormalities in non-thyroid illness may mimic or mask biochemical abnormalities observed in true thyroid disease.

Factors affecting the serum free thyroxine levels in hospitalized chronic geriatric patients

OBJECTIVE

Determination of whether nonthyroidal factors affect the diagnostic value of free thyroxine estimation in geriatric patients.

DESIGN

Survey.

PARTICIPANTS

A convenience sample of 381 non-selected, chronic, hospitalized geriatric patients over 60 years of age (I = relatively good health; II = relatively poor health; III = bad health; subgroups "sine therapia," ie, patients receiving no drugs that affect FT4) and 180 20-40 year old healthy persons.

MEASUREMENTS

Thyrotropin-releasing hormone test; thyrotropin (TSH); free thyroxine (FT4, measured in part by two parallel methods) estimation in a screening study; and thyroxine-binding globulin and thyroxine-binding-inhibitor activity measurements.

RESULTS

The normal FT4 ranges of the euthyroid geriatric (n = 210) and healthy young groups were similar. In the "sine therapia" euthyroid patients, FT4 decreased with age but increase with the severity of illness. High FT4 levels with non-suppressed TSH were more frequent in patients in poor and bad health. (I = 6/112; II = 14/140; III = 13/74; P < 0.01). The serum thyroxine-binding-inhibitor activity of euthyroid geriatric patients correlated with the severity of their clinical state (I = 6.22 +/- 5.65 (13); II = 7.40 +/- 4.33 (23); III = 10.04 +/- 5.50 (16) micrograms merthiolate equivalent/microL; ANOVA with log-transformed values: F(2.51) = 3.50, P < 0.05). The mean FT4 was higher in 36 heparin-treated patients (22.81 +/- 4.67 pmol/L) than in the 193 "sine therapia" patients (19.03 +/- 4.23 pmol/L; -P < 0.001). In a convenience subsample of 240 patients, a weak inverse correlation was found between FT4 and the thyroxine-binding globulin (r = -0.14, P < 0.02). Only 5/11 patients with low free thyroxine had hypothyroidism, while 11/46 patients with elevated free thyroxine had hyperthyroidism.

CONCLUSIONS

There is no need to modify the normal free thyroxine range for hospitalized geriatric patients. Clinical condition, drug treatment, and, to a lesser extent, age are factors that significantly affect the diagnostic value of FT4 in hospitalized chronic geriatric patients, decreasing the specificity of the test in diagnosing clinical hyper- and hypothyroidism.