Introduction: Thyroid function abnormalities are common in ICU patients, often presenting as non-thyroidal illness syndrome (NTIS) without primary thyroid disease. These changes are difficult to interpret but may reflect illness severity.

Aims and Objectives: To assess thyroid function status in patients admitted to the ICU of a tertiary care hospital in West Bengal and to describe the pattern of thyroid hormone alterations in critically ill patients.

Materials and Methods: This was a prospective, single-centre, hospital-based study conducted in the ICU of Midnapore Medical College & Hospital from 1st April 2021 to 31st March 2022. The study included 240 patients admitted to the ICU during the study period, and relevant clinical and laboratory parameters were recorded and analysed.

Results: The study population had a mean age of 44.15 ± 11.24 years, with most patients in the 41–50 years group (35.4%), and a male predominance (58.3%). Sepsis was the most common diagnosis (33.8%) and low FT3 was the most frequent thyroid abnormality (47.9%). Mortality was 29.6%, with non-survivors showing significantly higher APACHE scores, lower GCS, and markedly reduced FT3 levels, while other variables were not significantly associated with outcome.

Conclusion: Thyroid function abnormalities are common in ICU patients, with NTIS being the predominant pattern. These changes are more related to severity of illness rather than primary thyroid disease, highlighting the need for cautious interpretation of thyroid function tests in critically ill patients.

KEYWORDS: ICU, Thyroid Function Tests, Non-thyroidal Illness Syndrome, Critical Illness, Tertiary Care Hospital