[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [The pathology laboratory](https://durgical.com/en/general-pathology/#a-lab) › Cytology: the Pap test, fine-needle aspiration and body fluids [General pathology](https://durgical.com/en/general-pathology/) · [The pathology laboratory](https://durgical.com/en/general-pathology/#a-lab) # Cytology: the Pap test, fine-needle aspiration and body fluids - Technique Cytology looks at loose cells that were scraped, aspirated or floating in a fluid; it is cheap and fast, ideal for screening. Updated 2026-11-01 ## Key points - Cytology = loose cells: it sees atypia, not invasion. - Koilocytes = the cytopathic effect of HPV. - HSIL on cytology: colposcopy with biopsy. - Thyroid: aspiration diagnoses papillary carcinoma by its nuclei, but not follicular carcinoma. - A negative cytology does not exclude a tumour: sensitivity is limited, especially in fluids. ## What it is Cytology studies single cells, not tissue. They are obtained by scraping a surface (the Pap test), by fine-needle aspiration of a nodule, or from fluids such as pleural fluid, urine or cerebrospinal fluid. It is the basis of cervical cancer screening and of the work-up of a thyroid nodule, but it does not see architecture, so it cannot prove invasion. ## Structure - Koilocyte: a squamous cell with a clear halo around an enlarged, wrinkled, dark nucleus; the sign of HPV. - Dysplastic cell: large, dark nucleus with an irregular outline and little cytoplasm. - Papillary thyroid carcinoma on aspiration: nuclei with grooves, pseudoinclusions and pale chromatin. - Cell block: the sediment of a fluid is embedded in paraffin so immunohistochemistry can be done. ## Step by step - Cells are obtained: cervical brushing, aspiration of a nodule or centrifugation of a fluid. - They are smeared on a slide or suspended in a liquid medium that also allows HPV testing. - They are stained; the Pap test uses the Papanicolaou stain. - The cytologist assesses nuclear size and shape, the nuclear-to-cytoplasmic ratio and the chromatin. - The result is reported in standardised categories, each linked to a specific next step. - An abnormal result is confirmed on tissue: colposcopy and biopsy, or surgery. ## Cytology categories to know | Sample | Category | What it means | | --- | --- | --- | | Cervix | ASC-US | Atypical squamous cells of undetermined significance; resolved by HPV testing or follow-up | | [Cervix](https://durgical.com/en/conditions/human-papillomavirus-infection/) | LSIL | Low-grade squamous intraepithelial lesion, often transient HPV infection (koilocytes) | | [Cervix](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/) | HSIL | High-grade squamous intraepithelial lesion; needs colposcopy and biopsy | | [Cervix](https://durgical.com/en/conditions/endometrial-cancer/) | AGC | Atypical glandular cells; endocervix and endometrium must be studied | | [Thyroid](https://durgical.com/en/conditions/thyroid-nodule/) | Benign | Colloid nodule or thyroiditis; follow-up | | [Thyroid](https://durgical.com/en/conditions/follicular-oncocytic-and-anaplastic-thyroid-carcinoma/) | Follicular neoplasm | Adenoma cannot be separated from carcinoma: the surgical specimen is needed | | [Thyroid](https://durgical.com/en/conditions/thyroid-cancer/) | Malignant | Usually papillary carcinoma, recognised by its nuclei | | [Fluids](https://durgical.com/en/conditions/malignant-pleural-mesothelioma/) | Positive for malignancy | Tumour cells in the effusion: disseminated disease | ## Clinical notes - In Colombia and Latin America cervical cancer is still a major cause of cancer death in women; HPV testing is being added to cytology in screening. - The Pap test screens: an abnormal result is not a cancer diagnosis but an indication for colposcopy. - A thyroid nodule is studied with ultrasound-guided aspiration when its size or appearance calls for it. - A malignant pleural effusion in a person with cancer changes the stage; cytology can be negative even with disease, so it is sometimes repeated. ## Memory aid Cytology sees the face, biopsy sees the house: the face of the nucleus tells atypia; only the whole house shows invasion. ## Test yourself Think of the answer, then tap the question to see it. ## Which cell on a Pap test indicates an HPV effect? The koilocyte: a squamous cell with a clear perinuclear halo and an enlarged, wrinkled, dark nucleus. ## What follows a Pap test reported as HSIL? Colposcopy with biopsy of abnormal areas to confirm the lesion and rule out invasion. ## Why can cytology not diagnose an invasive carcinoma? Because it studies loose cells without tissue architecture, and invasion is only seen in tissue. ## Which thyroid carcinoma is diagnosed well by fine-needle aspiration? Papillary carcinoma, by its nuclear features: grooves, pseudoinclusions and pale chromatin. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/general-pathology/cytology-the-pap-test-fine-needle-aspiration-and-body-fluids/) ## Related - [Biopsy: excisional, incisional, core needle, punch and fine-needle aspiration](https://durgical.com/en/general-pathology/biopsy-excisional-incisional-core-needle-punch-and-fine-needle-aspiration/) - [Dysplasia and carcinoma in situ](https://durgical.com/en/general-pathology/dysplasia-and-carcinoma-in-situ/) - [Frozen section: the intraoperative consultation](https://durgical.com/en/general-pathology/frozen-section-the-intraoperative-consultation/) - [Immunohistochemistry: the principle and the markers to know](https://durgical.com/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/) - [Oncogenic viruses and H. pylori: the table to know](https://durgical.com/en/general-pathology/oncogenic-viruses-and-h-pylori-the-table-to-know/) - [Precancerous conditions: when chronic inflammation, metaplasia or hyperplasia raise the risk](https://durgical.com/en/general-pathology/precancerous-conditions-when-chronic-inflammation-metaplasia-or-hyperplasia-rais/) ## Related conditions - [Cervical intraepithelial neoplasia (cervical dysplasia)](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/) - [Cervical cancer](https://durgical.com/en/conditions/cervical-cancer/) - [Human papillomavirus (HPV) infection](https://durgical.com/en/conditions/human-papillomavirus-infection/) - [Thyroid cancer (papillary)](https://durgical.com/en/conditions/thyroid-cancer/) - [Thyroid nodule](https://durgical.com/en/conditions/thyroid-nodule/) - [Follicular, oncocytic (Hürthle cell) and anaplastic thyroid carcinoma](https://durgical.com/en/conditions/follicular-oncocytic-and-anaplastic-thyroid-carcinoma/) - [Bladder cancer](https://durgical.com/en/conditions/bladder-cancer/) - [Lung cancer](https://durgical.com/en/conditions/lung-cancer/) - [Malignant pleural mesothelioma](https://durgical.com/en/conditions/malignant-pleural-mesothelioma/) - [Breast cancer](https://durgical.com/en/conditions/breast-cancer/) - [Cervical lymphadenopathy](https://durgical.com/en/conditions/cervical-lymphadenopathy/) - [Endometrial cancer](https://durgical.com/en/conditions/endometrial-cancer/) ## Elsewhere in DurgiPedia - [Cervix and vagina: the transformation zone](https://durgical.com/en/histology/cervix-and-vagina-the-transformation-zone/) - [Thyroid follicles, C cells and parathyroid](https://durgical.com/en/histology/thyroid-follicles-c-cells-and-parathyroid/) - [Simple, stratified, pseudostratified and transitional epithelium](https://durgical.com/en/histology/simple-stratified-pseudostratified-and-transitional-epithelium/) ## Microorganisms - [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Pap Smear: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/pap-smear/) (MedlinePlus, US National Library of Medicine, 2024); [Fine needle aspiration of the thyroid: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003899.htm) (MedlinePlus, US National Library of Medicine, 2024); [Cervical Cancer](https://www.ncbi.nlm.nih.gov/books/NBK431093/) (StatPearls (NCBI Bookshelf), 2024); [Thyroid Nodule](https://www.ncbi.nlm.nih.gov/books/NBK535422/) (StatPearls (NCBI Bookshelf), 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/cytology-the-pap-test-fine-needle-aspiration-and-body-fluids/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/cytology-the-pap-test-fine-needle-aspiration-and-body-fluids/