# Bethesda category (thyroid cytology)

Source: https://onco.cc/terms/bethesda-category/  
OnCo record `bethesda-category` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The Bethesda category is a six-step scale, from 'not enough cells' to 'cancer', that pathologists use to report a thyroid needle biopsy.

## Summary

The Bethesda category is the six-step scale that pathologists use to report a thyroid needle biopsy: I non-diagnostic, II benign, III atypia of undetermined significance, IV follicular neoplasm, V suspicious and VI malignant. Readers meet it in the entry on thyroid nodule fine-needle aspiration, Bethesda cytology and molecular classifiers, because categories III and IV are the indeterminate zone where molecular classifiers change management. The 2023 revision of the system harmonised the estimated risk of malignancy attached to each category. The category matters for overdiagnosis: how indeterminate nodules are handled decides how many are sent to surgery, which is why the overdiagnosis bottleneck links to it.

## Fields

- Kind: Term
- Last checked: 2026-09-07

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Bethesda_System_for_Reporting_Thyroid_Cytopathology
- The 2023 Bethesda System for Reporting Thyroid Cytopathology (Ali et al., Thyroid 2023): https://doi.org/10.1089/thy.2023.0141

## Connected records

- cancers: [Thyroid cancer](https://onco.cc/cancers/thyroid/)
- technologies: [Thyroid nodule FNA, Bethesda cytology & molecular classifiers](https://onco.cc/technologies/thyroid-fna-molecular/)
- key papers: [The 2023 Bethesda System for Reporting Thyroid Cytopathology](https://onco.cc/key-papers/paper-ali-thyroid/)
- bottlenecks: [Overdiagnosis and false alarms](https://onco.cc/bottlenecks/b-overdiagnosis/)

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