Thyroid gland
Bethesda guidelines for Cytology

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

Revised: 13 January 2017, last major update June 2014

Copyright: (c) 2014-2017,, Inc.

PubMed Search: Bethesda guidelines thyroid
Cite this page: Adequacy. website. Accessed May 25th, 2018.
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's, 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 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