Factors Affecting the Serum Free Thyroxine Levels in Hospitalized Chronic Geriatric Patients

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