Thyroid gland
Bethesda guidelines for cytology

Author: Phillip A. Williams, M.D., M.Sc., Shahidul Islam, M.D., Ph.D. (see Authors page)

Revised: 30 July 2018, last major update June 2014

Copyright: (c) 2014-2018,, Inc.

PubMed Search: Bethesda guidelines thyroid
Page views in 2018: 2,294
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Cite this page: Williams, P.A., Islam, S. Adequacy. website. Accessed January 21st, 2019.
Definition / general
  • Definition of adequacy (minimum number of follicular cells present) depends on the nature of the lesion
  • Solid nodules: at least 6 well preserved, undistorted and well stained follicular groups, each containing at least 10 cells; preferably follicular groups present on the same slide
  • This minimum size allows evaluation of macrofollicles (Acta Cytol 1987;31:587, Surgery 1989;106:980)
  • Several exceptions for this quantitative requirement include:
    • Any sample with significant cytological atypia, regardless of cellularity, is considered adequate
    • For solid nodules that have numerous inflammatory cells (e.g., Hashimoto, abscess, granulomatous thyroiditis), there is no minimum number of follicular cells required
    • Colloid nodules with abundant thick colloid: no requirement for a minimum number of follicular cells for this benign diagnosis
Unsatisfactory / nondiagnostic
  • Ideally, should be less than 10% of all thyroid FNAs (in practice: 2 - 20%) (Cancer 2000;90:357, Am J Clin Pathol 2001;116:477, Cancer 2007;111:306)
  • Inadequate numbers of follicular cells, i.e., less than 6 well preserved, undistorted and well stained follicular groups, each containing at least 10 cells is unsatisfactory
  • Obscured (e.g., due to blood, gel), poorly visualized, poorly preserved or poorly preserved stains are unsatisfactory
  • Overly thick smears
  • Air drying of alcohol fixed smears
  • Thyroid cysts with histiocytes and with little or no follicular cells are nondiagnostic and may be interpreted as "cyst fluid only"; no strict requirement for a minimum number of groups of follicular cells for these lesions; may add a comment: "cystic papillary carcinoma cannot be ruled out"
  • Presence of only nonthyroid tissue (e.g., muscle, cartilage) with no follicular cells is unsatisfactory
Cytology images

Images hosted on PathOut server:

Contributed by Ayana Suzuki, Cytotechnologist, Japan:

Hemorrhagic background


Respiratory epithelium

Air dried smear

Cyst fluid only

Images hosted on other servers:


Sparsely cellular

Cyst fluid only


Precipitated stain

Blood and precipitated stain

Blood and macrophages only

Blood and drying artifact

Skeletal muscle only

Air drying artifact

Blood only