Acute Systemic Oxidative Stress Response to Fine-Needle Aspiration Biopsy in Thyroid Nodules

Background/Objectives: Fine-needle aspiration biopsy (FNAB) is the primary diagnostic procedure for the evaluation of thyroid nodules. Although considered safe and minimally invasive, its immediate systemic biochemical effects, particularly those related to oxidative stress and mechanical tissue injury, remain insufficiently characterized. This study aimed to evaluate the acute systemic impact of FNAB on oxidative stress parameters and to determine whether these changes correlate with cytological malignancy risk. Methods: A total of 208 patients undergoing ultrasound-guided FNAB for a solitary thyroid nodule were prospectively included. Venous blood samples were collected in the supine position immediately before and within 1 min after the procedure. Thiol–disulfide homeostasis parameters were measured using an automated spectrophotometric method, and ischemia-modified albumin (IMA) levels were analyzed concurrently. Pre- and post-procedural values were compared using the Wilcoxon signed-rank test. Associations between oxidative stress markers and Bethesda cytological categories were assessed using Spearman’s correlation analysis. Results: Native thiol and IMA levels demonstrated statistically significant changes following FNAB, whereas total thiol, disulfide levels, and derived thiol–disulfide ratios remained unchanged. The reduction in IMA levels was predominantly observed in lower-risk cytological categories. No significant correlations were identified between oxidative stress parameters and Bethesda-based malignancy risk. Conclusions: FNAB induces only minor and transient alterations in selected systemic oxidative stress markers, which are clinically inconsequential. The observed changes in native thiol and IMA levels appear to reflect short-term procedural effects rather than malignancy-associated redox alterations. These findings support the systemic safety of FNAB and emphasize the need for careful temporal standardization when interpreting circulating oxidative biomarkers in thyroid nodule research.