FACTORS AFFECTING THE SERUM-FREE THYROXINE LEVELS IN HOSPITALIZED CHRONIC GERIATRIC-PATIENTS

Objective: Determination of whether nonthyroidal factors affect the di agnostic value of free thyroxine estimation in geriatric patients. Des ign: Survey. Participants: A convenience sample of 381 non-selected, c hronic, hospitalized geriatric patients over 60 years of age (I = rela tively good health; II = relatively poor health; III = bad health; sub groups ''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, measu red in part by two parallel methods) estimation in a screening study; and thyroxine-binding globulin and thyroxine-binding-inhibitor activit y measurements. Results: The normal FT4 ranges of the euthyroid geriat ric (n = 210) and healthy young groups were similar. In the ''sine the rapia'' euthyroid patients, FT4 decreased with age but increase with t he severity of illness. High FT4 levels with non-suppressed TSH were m ore frequent in patients in poor and bad health. (I = 6/112; II = 14/1 40; III = 13/74; P < 0.01). The serum thyroxine-binding-inhibitor acti vity of euthyroid geriatric patients correlated with the severity of t heir clinical state (I = 6.22 +/- 5.65 (13); II = 7.40 +/- 4.33 (23); II = 10.04 +/- 5.50 (16) mug merthiolate equivalent/muL; ANOVA with lo g-transformed values: F(2,51) = 3.50, P < 0.05). The mean FT4 was high er 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 w as 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 hyperthyroidis m. Conclusions: There is no need to modify the normal free thyroxine r ange for hospitalized geriatric patients. Clinical condition, drug tre atment, and, to a lesser extent, age are factors that significantly af fect the diagnostic value of FT4 in hospitalized chronic geriatric pat ients, decreasing the specificity of the test in diagnosing clinical h yper- and hypothyroidism.