Predictors and Mortality Determinants of Non-Thyroidal Illness Syndrome Among Patients in the Medical Intensive Care Unit in Northeastern Tanzania

Background: Non-thyroidal illness syndrome (NTIS) frequently occurs in critically ill patients and reflects alterations in thyroid hormone metabolism without intrinsic thyroid disease. It has been increasingly recognized as a potential marker of disease severity and poor outcomes in intensive care settings, yet data from Sub-Saharan Africa remain limited. To determine the prevalence of NTIS and identify determinants of mortality among patients admitted to a medical intensive care unit (ICU) in northern Tanzania. Methods: We conducted a prospective cohort study among 120 adult patients admitted to the medical ICU at a tertiary referral hospital between October 2024 and March 2025. Thyroid function tests (T3, T4, and TSH) were measured within 24 hours of admission. NTIS was defined based on characteristic biochemical patterns in the absence of known thyroid disease. Clinical, laboratory, and outcome data were collected prospectively. Associations were assessed using Chi-square tests and modified Poisson regression to estimate adjusted risk ratios (aRR) with 95% confidence intervals. Results: The prevalence of NTIS was 23.3%. Overall mortality was 42.5%, with significantly higher mortality among patients with NTIS (67.9%) compared with those without NTIS (34.8%). NTIS remained independently associated with mortality after adjustment (aRR 8.05; 95% CI: 2.27-28.56; p=0.001). Patients with NTIS were also more likely to experience prolonged hospital stays. Although several clinical variables showed associations in bivariate analysis, most did not remain significant after adjustment. Illness severity, as reflected by clinical scoring systems, remained an important contributor to outcomes. Conclusion: NTIS is common among critically ill patients and is strongly associated with increased mortality. It may serve as a practical prognostic marker in ICU settings, particularly in resource-limited environments. Further multicenter studies are needed to validate its prognostic utility and integration into routine clinical practice.