Objective:

To identify predictors of false-negative unstimulated serum Tg (<0.2 ng/mL) in patients with persistent/recurrent cervical lymph nodes of papillary thyroid carcinoma and develop a predictive model for monitoring.

Approach:

Key Findings:

• 22.3% of patients had unstimulated serum Tg <0.2 ng/mL, indicating a significant proportion of false-negative results.
• Independent predictors of false-negative Tg included central LN compartment (p = 0.039), smaller LN size (p = 0.019), and higher Tg−Ab level (p < 0.001).
• In Tg−Ab negative patients, higher Tg−Ab remained associated with false-negative Tg (p < 0.001).
• The nomogram showed good discrimination (AUC = 0.87) and calibration.

Interpretation:

Central LN location, small LN size, and elevated Tg−Ab are associated with false−negative Tg in Papillary Thyroid Carcinoma patients with persistent/recurrent LNs.

Limitations:

• The study is retrospective and may have inherent biases.
• Exclusion criteria may limit generalizability of findings, particularly regarding the specific patient population studied.

Conclusion:

The nomogram identifies high-risk individuals (≥0.1) in whom serum Tg alone is unreliable.

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