Given my normal TSH and free T4, negative thyroid antibodies, low but detectable thyroglobulin levels over time, a total thyroidectomy for papillary carcinoma six years ago with negative lymph‑node mapping and abdominal CT, and a 4‑mm Lung‑RADS 2 pulmonary nodule, is there any evidence of recurrent papillary thyroid cancer?

Your thyroglobulin levels and imaging findings do NOT indicate recurrent papillary thyroid carcinoma

Based on your post-thyroidectomy surveillance data, you fall into the "acceptable response" category with very low risk of clinically significant recurrence, and the 4-mm pulmonary nodule is almost certainly benign and unrelated to your thyroid cancer.

Thyroglobulin Interpretation

Your thyroglobulin trend is reassuring:

• All values are <3 ng/mL (ranging 0.9-2.7 ng/mL over time)
• These are measured while on thyroid hormone suppression (unstimulated)
• Your thyroid antibodies are negative, making these values reliable

According to current guidelines, patients after total thyroidectomy with radioiodine ablation should have:

• Stimulated Tg <1 ng/mL for excellent response 1
• Unstimulated Tg <0.2 ng/mL for excellent response 1

Your unstimulated values of 0.9-2.7 ng/mL place you in the "acceptable response" category 1. This means:

• Undetectable basal Tg with stimulated Tg <10 ng/mL
• Trend of Tg stable or declining (yours shows fluctuation but no clear upward trend)
• Substantially negative imaging

Patients in this category require closer follow-up but have low risk of recurrence (<5%) and typically do not require additional treatment unless disease progression is documented 1, 2.

Critical Context from Recent Evidence

A 2025 study of 1,818 papillary thyroid carcinoma patients found that unstimulated Tg ≥3 ng/mL was the threshold associated with increased recurrence risk 3. Your highest value of 2.7 ng/mL falls just below this cutoff. More importantly, research shows that patients with unstimulated Tg <3 ng/mL and stable/declining Tg doubling rate have excellent long-term outcomes 3.

Another key study demonstrated that even patients with clinically apparent lymph node metastases (cN1) who had unstimulated Tg <0.3 ng/mL after surgery showed only 3.6% recurrence over median 84-month follow-up 4. Your values, while slightly higher, remain in a favorable range.

The Pulmonary Nodule

The 4-mm Lung-RADS 2 nodule is not concerning for thyroid cancer metastasis:

• Lung-RADS 2 = benign appearance with 1-year follow-up recommended based on risk factors
• Thyroid cancer pulmonary metastases typically present as:
  • Multiple bilateral nodules (not solitary)
  • Associated with markedly elevated thyroglobulin (typically >10 ng/mL) 2
  • Visible on radioiodine whole-body scan if iodine-avid

Guidelines specifically state that CT chest should be considered in high-risk patients with elevated serum thyroglobulin (>10 ng/mL) or rising thyroglobulin antibodies with negative neck imaging 2. Your Tg levels do not meet this threshold.

Recommended Surveillance Strategy

Based on your risk profile, you should follow this algorithm:

Every 6-12 months:

• Physical examination
• Neck ultrasound (thyroid bed and cervical lymph nodes) 2
• Unstimulated thyroglobulin measurement on levothyroxine 1

Additional testing NOT routinely indicated:

• Stimulated thyroglobulin testing (may be considered if unstimulated Tg rises above 3 ng/mL or shows clear upward trend) 1
• Whole-body radioiodine scan (not indicated with stable low Tg and negative ultrasound) 2
• FDG-PET/CT (not recommended for routine surveillance without structural disease) 2

For the lung nodule:

• Follow standard Lung-RADS 2 recommendations: repeat chest CT in 12 months
• This is unrelated to thyroid cancer surveillance

Key Pitfalls to Avoid

1. Do not over-interpret small Tg fluctuations: Values between 0.9-2.7 ng/mL represent assay variability and minimal residual thyroid tissue, not necessarily viable cancer 1, 5

2. Do not assume every pulmonary nodule is metastatic: Solitary small nodules with benign imaging characteristics are common incidental findings unrelated to thyroid cancer

3. Recognize that detectable Tg ≠ recurrence: Up to 20% of patients have persistently low but detectable Tg without structural disease that remains stable for years 2

4. TSH suppression on current dose (TSH 0.877): Your TSH is appropriately suppressed. For patients with acceptable response and no structural disease, TSH can be maintained at 0.1-0.5 mIU/L rather than <0.1 mIU/L 6, 1

When to Escalate Surveillance

Trigger additional imaging (neck CT with contrast, consider chest CT, possibly FDG-PET) if:

• Unstimulated Tg rises above 3 ng/mL 3
• Clear upward Tg trend over serial measurements
• Suspicious findings on neck ultrasound
• Development of palpable neck masses

Your current data do not meet any of these criteria.