The significance of high thyroxine in hospitalized patients with low thyroid-stimulating hormone

Purpose There is scarce data about the interpretation of high thyroid hormone levels in hospitalized patients. We wished to investigate the significance of high thyroxine (T4) in hospitalized patients with low TSH. Methods We conducted a retrospective study of data from patients in nonsurgical departments. Three groups of random patients with low TSH were defined and compared: 123 patients with only high FT4 levels (T4 group), 82 with high FT3 levels with or without high FT4 level (T3 group), and 119 with low FT3 and FT4 level in the lower half of the norm and below (NTIS group). Results The primary cause of admission in the T4 and NTIS groups was infectious disease, 20.3% and 40.3%, respectively; while in the T3 group it was cardiovascular disease (31.7%). The T4 group but not T3 group had epidemiological and clinical characteristics similar to the NTIS group. The T4 group had a significant correlation between increased CRP levels and decreased FT3 (r = 0.366,p < 0.001) similar to the NTIS group. The T3 group had a borderline correlation between increased FT3 and FT4 levels (r = 0.208,p = 0.061) but the T4 group did not. Conclusions The combination of low TSH and high FT4 levels in hospitalized patient is usually caused by nonthyroidal illness combined with drug effects. This thyroid function disturbance is common in hospitalized patients and if the FT3 level is below the middle of the norm, treatment is probably unnecessary.