Low T3 syndrome as a prognostic factor in patients in the intensive care unit: an observational cohort study

ABSTRACT Objective: To assess euthyroid sick syndrome as a prognostic factor in patients in the intensive care unit; to detect factors that may affect mortality; and to develop an equation to calculate death probability. Methods: This was a longitudinal, observational, nonconcurrent cohort study developed in the intensive care unit of Fundação Santa Casa de Misericórdia do Pará. One hundred adults with no prior documented endocrinopathy were submitted to a 20mL blood sample collection for the measurement of thyroid stimulating hormone, free tetraiodothyronine, free triiodothyronine and reverse triiodothyronine. Results: Most patients were female, aged 20 to 29 years. Most patients who died were older (median age of 48 years), and euthyroid sick syndrome was present in 97.5% of them. Euthyroid sick syndrome was related to death, comorbidities, age and length of stay in the intensive care unit (median of 7.5 days). There was an association between lower thyroid stimulating hormone and death. Patients with free triiodothyronine levels below 2.9pg/mL were more likely to die; reverse triiodothyronine rates were above 0.2ng/mL in those who died. Free triiodothyronine had greater sensitivity and accuracy, and reverse triiodothyronine had greater specificity to predict mortality. Based on the results and cutoff points, a multiple logistic regression formula was developed to calculate the probability of death. Conclusion: The main limitation of this study is the fact that it was conducted in a reference hospital for maternal and child care; therefore, there was a greater number of female patients and, consequently, a sampling bias existed. However, opportune measurement of free and reverse triiodothyronine levels in critical patients and application of the proposed equation are suggested.

摘要
研究目的：评估甲状腺功能正常的病态综合征（euthyroid sick syndrome）作为重症监护病房（intensive care unit, ICU）患者预后因素的价值；明确可能影响患者死亡的相关因素；并构建死亡概率计算方程。
研究方法：本研究为一项在帕拉州圣家慈善基金会（Fundação Santa Casa de Misericórdia do Pará）重症监护室开展的纵向观察性非同期队列研究。纳入100名既往无明确内分泌疾病病史的成年患者，采集20mL血液标本，用于检测促甲状腺激素（thyroid stimulating hormone, TSH）、游离甲状腺素（free tetraiodothyronine, FT4）、游离三碘甲状腺原氨酸（free triiodothyronine, FT3）及反三碘甲状腺原氨酸（reverse triiodothyronine, rT3）水平。
研究结果：本研究纳入的患者多数为女性，年龄集中在20~29岁区间。死亡患者的年龄普遍更高（中位年龄为48岁），其中97.5%存在甲状腺功能正常的病态综合征。甲状腺功能正常的病态综合征与患者死亡、合并症、年龄及重症监护室住院时长（中位时长7.5天）显著相关。较低的促甲状腺激素水平与患者死亡存在关联。游离三碘甲状腺原氨酸水平低于2.9pg/mL的患者死亡风险更高；死亡患者的反三碘甲状腺原氨酸水平均高于0.2ng/mL。游离三碘甲状腺原氨酸对死亡预测的灵敏度与准确度更佳，反三碘甲状腺原氨酸的特异性更高。基于上述研究结果及临界值，本研究构建了多元logistic回归方程以计算患者死亡概率。
研究结论：本研究的主要局限性在于，其开展于一所妇幼保健参考医院，因此女性患者占比更高，存在抽样偏倚。但本研究建议，对危重症患者及时检测游离三碘甲状腺原氨酸与反三碘甲状腺原氨酸水平，并应用本研究提出的死亡概率计算方程。