Background: Procalcitonin (PCT) is secreted by C cells in the thyroid, neuroendocrine cells, and parenchymal tissues in response to bacterial infection. Using a cutoff of 0.5 ng/mL, PCT can detect bacterial sepsis with a sensitivity and specificity of 94% and 88%, respectively. It is unknown how much thyroid tissue contributes to PCT production relative to other tissues in the setting of bacterial sepsis, and how hypothyroidism impacts test performance.
Objective: Determine whether hypothyroidism affects the ability of PCT to predict bacterial sepsis compared to euthyroid controls.
Methods: Retrospective review of randomly selected patients with and without hypothyroidism who underwent PCT testing at UCLA in 2017. Bacterial sepsis was defined by criteria set by the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). Patients were classified as hypothyroid if they received thyroid supplementation, and euthyroid if they had a normal TSH without thyroid hormone supplementation.
Results: Of the patients eligible for this study, we randomly selected 131 patients for review. Of these patients, 77 were euthyroid and 54 were hypothyroid. The primary reason for admission was suspected infection in 88% of these patients, 8% were admitted for elective surgery, and 4% for trauma. Of the 107 patients with suspected infection, pneumonia was the most common presumed diagnosis (57%) followed by UTI (9%). Overall, 65 patients met sepsis-3 criteria. The hypothyroid patients were older than the euthyroid patients (67 (20)vs 59 (18) years, p=0.02) and had a higher proportion of female patients (70% vs 38%, p<0.001). There was no statistically significant difference in mean peak procalcitonin for hypothyroid patients compared to euthyroid patients. Using a cut-off of 0.5 ng/ml, PCT predicted sepsis in euthyroid patients with a sensitivity of 52.8% and specificity of 82.9%. In hypothyroid patients, PCT had a sensitivity of 62.1% and specificity of 84% for the detection of sepsis.
Conclusions: In our limited series, hypothyroidism is not associated with decreased PCT levels, and does not impact the ability of PCT to predict bacterial sepsis compared to euthyroid patients.