How do I order a thyroid fine‑needle aspiration biopsy?

How to Order a Thyroid Fine-Needle Aspiration Biopsy

Thyroid fine-needle aspiration biopsy (FNAB) should be performed by an experienced operator under ultrasound guidance using a 23-27 gauge needle, and must be ordered based on specific EU-TIRADS classification and size criteria rather than for all thyroid nodules. 1

Pre-Biopsy Assessment Requirements

Determine TSH Level First

• Measure serum TSH before proceeding with FNAB 1
• If TSH < 0.4 mIU/L: Order thyroid scintigraphy first to identify autonomous (hot) nodules 1
• If TSH 0.4-1 mIU/L: Order scintigraphy only if FNAB is already indicated based on ultrasound criteria 1
• If TSH ≥ 1 mIU/L: Proceed directly to ultrasound-based assessment without scintigraphy 1
• Do not perform FNAB on autonomous nodules when TSH is in the low-normal range (< 1 mU/L) 1

Apply EU-TIRADS Size Criteria

The decision to order FNAB depends on both the EU-TIRADS score and nodule size 1:

For solid nodules:

• EU-TIRADS 5 nodules ≤ 10mm: Do not order routine FNAB 1
• EU-TIRADS 5 nodules > 10mm: Order FNAB 1
• EU-TIRADS 4 nodules: Order FNAB if > 10mm 1
• EU-TIRADS 3 nodules: Order FNAB only if ≥ 20mm 1

For mixed (cystic-solid) nodules:

• Measure only the solid tissue portion separately from the fluid component 1
• Order FNAB based on EU-TIRADS score of the solid portion if it is accessible and > 10mm 1

Multiple Nodules Strategy

• Order FNAB for 2-3 nodules maximum, prioritizing those most likely to be cancerous based on EU-TIRADS score and size 1
• Assess each nodule individually according to its own size and EU-TIRADS classification 1

Ordering the Procedure

Technical Specifications to Include

When ordering the FNAB, specify 1:

• Ultrasound-guided procedure (not palpation-guided) 1
• 23-27 gauge needle 1
• Request experienced operator when possible 1
• Aspiration technique vs. non-aspiration depends on nodule characteristics (operator will determine) 1

Anticoagulation Management

• Assess risk/benefit ratio of discontinuing anticoagulation on an individual basis 1
• This requires case-by-case clinical judgment rather than routine discontinuation 1

Required Clinical Information

Include a requisition form with the following details 1:

• Complete ultrasound characteristics of the nodule (size, EU-TIRADS score, echogenicity, calcifications, borders, vascularity)
• Clinical context (TSH level, symptoms, family history, radiation exposure)
• Whether this is an initial biopsy or repeat procedure 1

Special Considerations

When Calcitonin Measurement is Needed

• Measure calcitonin before any thyroid surgery or thermal ablation 1
• Normal calcitonin does not need to be repeated unless genetic predisposition to medullary thyroid cancer exists 1

Hypermetabolic Nodules on PET Scan

If incidental 18F-FDG uptake is present 1:

• Order FNAB for all hypermetabolic nodules > 1cm classified as EU-TIRADS 4 or 5
• Order FNAB for hypermetabolic EU-TIRADS 3 nodules ≥ 2cm

After Non-Diagnostic Results

• If FNAB yields non-diagnostic results twice, order microbiopsy (core needle biopsy) for solid nodules 1

What NOT to Order

• Do not order CT or MRI for routine initial thyroid nodule assessment 1
• CT/MRI reserved only for: substernal extension assessment, tracheal/esophageal compression evaluation, preoperative vascular mapping, or lymph node mapping 1
• Do not order FNAB for nodules that don't meet size/EU-TIRADS criteria above 1

Common Pitfalls to Avoid

• Ordering FNAB on small (≤10mm) EU-TIRADS 5 nodules—these should be monitored, not biopsied 1
• Failing to check TSH first and potentially biopsying autonomous nodules unnecessarily 1
• Ordering biopsies on multiple nodules without prioritizing by malignancy risk 1
• Not providing adequate clinical information to the cytopathologist, which reduces diagnostic accuracy 1