Low free T3 levels associated with COVID-19 mortality, ICU admission

ByMichael Monostra

Add topic to email alerts

Please provide your email address to receive an email when new articles are posted on Thyroid.

Euthyroid adults hospitalized with COVID-19 who had lower free triiodothyronine levels had more ICU admissions, mechanical ventilation and mortality compared with those with higher levels, according to researchers.

“The implications of the findings are to provide another potential evaluation tool for the physician treating COVID-19 patients,” Yair Schwarz, MD, MPH, of the Dalia and David Arabov Endocrinology and Diabetes Research Center at Sheba Medical Center in Tel Hashomer, Israel, told Healio. “This tool doesn't replace clinical evaluation, which is the most important skill when evaluating patients. But when clinical evaluation is equivocal, and especially considering the great burden on the medical systems, every decision-supporting tool is valuable.”

COVID-19 patients with low free T₃levels had a higher mortality rate compared with those with higher levels.

Researchers conducted a retrospective study of 54 adults hospitalized at Sheba Medical Center with COVID-19 between Feb. 27 and July 30, 2020. Patients who had a full thyroid function profile were included in the analysis. Demographic data, medical history, laboratory parameters and thyroid function test results were analyzed, and the Charlson comorbidity index score was calculated for each person. The study population was divided into tertiles based on free T3 levels: 2.4 pmol/L to 4 pmol/L, 4.1 pmol/L to 4.8 pmol/L, and 4.9 pmol/L to 7.4 pmol/L. Researchers also collected data on mechanical ventilation, transfer between wards and mortality.

Patients in the lowest free T₃tertile were older (mean age, 68.7 years) compared with those in the middle tertile (mean age, 56.7 years) and highest tertile (mean age, 48.9 years; P = .006). Adults in the lowest tertile also had a higher prevalence of diabetes and higher Charlson comorbidity index scores compared with the two higher tertiles. No significant differences in BMI, sex, hypertension, ischemic heart disease, congestive heart failure, autoimmune disease or diagnosis of cognitive decline were found among the three groups. Adults in the lowest free T₃tertile had lower mean room air oxygen saturation than the two higher groups and were the only tertile to have patients requiring mechanical ventilation in the ED (n = 5).

“We expected to find an association,” Schwarz said. “What surprised us was the robustness of the association and the high significance it retained when adjusted to other variables.”

Adults in the low free T₃tertile had a higher mortality rate (40%) compared with the middle tertile (5.9%) and the high T₃group (5.9%; P = .008). The lowest tertile also had a higher prevalence of mechanical ventilation (45%) vs. the middle (29.4%) and highest tertiles (0%; P =.007). A higher proportion of adults were admitted to the ICU from the low free T₃cohort (55%) compared with the middle tertile (29.4%) and the highest tertile (5.9%; P = .006).

Of the 10 patients who died, eight were in the low free T₃tertile. Adults who died in that tertile had a lower mean free T₃at presentation than those who survived (3.45 pmol/L vs. 4.65 pmol/L; P < .001). Those who died were also older than those who survived (74.9 years vs. 55 years; P = .03) and had a higher Charlson comorbidity index score (6.1 vs. 2.48; P < .001). After adjusting for age, Charlson comorbidity index, white blood count, neutrophil count and albumin, free T₃was an independent predictor for mortality.

The researchers wrote that the study had several limitations, including the small study population size and that thyroid function tests were not available to all patients at admission. However, they concluded that free T₃levels can be a strong predictor for COVID-19 outcomes.

“Future research concerning sick euthyroid syndrome should focus on the old-time question of whether treatment of the syndrome provides any benefit concerning morbidity and mortality,” Schwarz said. “Today there is a lack of current high-quality research in the area.”