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Bethesda System (Thyroid FNA)

Bethesda Thyroid System

Cytopathology Management Suite

Cytology Category

Category Logic

Select a Bethesda category to see the malignancy risk and standard management path.

Guidelines & Evidence

Verified

Last Review: 2026

When to Use

What is the Bethesda System?

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) is a standardized 6-tier classification system for thyroid fine-needle aspiration (FNA) results. It provides a uniform framework for cytopathology reporting, ensuring consistent communication between pathologists and clinicians. Each category includes a specific diagnosis, estimated risk of malignancy (ROM), and evidence-based management recommendations. The system was first published in 2007 and updated in 2017 to incorporate new data, including the reclassification of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) as a non-malignant entity.

Primary Indications

Thyroid nodule evaluation – Reporting cytology results for all thyroid FNAs performed for diagnostic evaluation of thyroid nodules (incidental or palpable)

Risk stratification – Providing standardized malignancy risk estimates (ROM) to guide management decisions

Guideline-concordant care – Enabling adherence to ATA (American Thyroid Association) and NCCN (National Comprehensive Cancer Network) clinical practice guidelines

Research and quality improvement – Standardizing data collection across institutions, enabling meta-analyses and comparative effectiveness research

Patient communication – Providing clear, evidence-based language for discussing results with patients (e.g., "Your nodule is Bethesda II, benign, with <3% risk of cancer")

Surgical triage – Identifying nodules requiring surgical resection (Bethesda IV-VI) vs those appropriate for surveillance (Bethesda II) vs those needing repeat FNA or molecular testing (Bethesda I, III)

Medicolegal documentation – Creating a documented standard of care for thyroid nodule management

When to Perform Thyroid FNA (Per ATA Guidelines)

Nodules ≥1.0 cm with high-suspicion ultrasound features (solid, hypoechoic, irregular margins, taller-than-wide, microcalcifications)

Nodules ≥1.5 cm with intermediate-suspicion ultrasound features (hypoechoic solid nodule without high-suspicion features)

Nodules ≥2.0 cm with low-suspicion ultrasound features (isoechoic or hyperechoic solid nodule, or partially cystic with other low-suspicion features)

Nodules with concerning features regardless of size (cervical lymphadenopathy, rapid growth, extra-thyroidal extension, suspicious cervical lymph nodes)

Nodules with prior Bethesda I (nondiagnostic) result – repeat FNA recommended

Nodules with prior Bethesda III (AUS/FLUS) result – repeat FNA or molecular testing

Comparison with Other Thyroid Reporting Systems

System	Tiers	Focus	Risk Estimates	Geographic Use	Advantages
Bethesda (TBSRTC)	6 tiers (I-VI)	Cytopathology + management	Yes (ROM by tier)	International (US, Europe, Asia, Australia)	Most widely adopted, standardized terminology, management recommendations included, updated 2017 with NIFTP
British Thyroid Association (Thy) System	5 tiers (Thy 1-5)	Cytopathology only (referral to guidelines for management)	Yes (ROM by tier)	United Kingdom, Europe	Simpler (5 tiers), integrated with UK guidelines, but fewer categories than Bethesda
Japanese System	5 categories	Cytopathology + management	Yes	Japan	Different categories (e.g., "follicular neoplasm" separate from "suspicious for malignancy")
Italian Consensus (SIAPEC)	5 classes (TIR 1-5)	Cytopathology only	Yes	Italy	Similar to Bethesda but 5 tiers, TIR-3 split into low-risk and high-risk subgroups
Papanicolaou Society System	6 categories	Pancreatic/biliary cytology (not thyroid)	Yes	US, Europe	Analogous to Bethesda but for pancreas
TI-RADS (Thyroid Imaging Reporting and Data System)	5 levels (TR 1-5)	Ultrasound imaging	Yes (based on imaging features, not cytology)	International	Imaging-based risk stratification, guides which nodules need FNA

Related Scores in Practice

In clinical practice, this assessment is frequently evaluated alongside other validated measures. Depending on the patient's presentation and specific diagnostic requirements, you may also need to utilize the Ti Rads Thyroid, Thyroid Nodule Risk Calculator, Thyroglobulin or the Procalcitonin Stop Rule to formulate a comprehensive care plan.

Last Comprehensive Review: 2026

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