Introduction
- Cytology is the microscopic study of individual cells or small groups of cells for diagnostic purposes.
- It is an important branch of laboratory medicine used for early detection of inflammatory, infectious, premalignant, and malignant lesions.
- Cytology examines cellular morphology rather than tissue architecture, which distinguishes it from histopathology.
- Major cellular features assessed in cytology include nuclear size, chromatin pattern, cytoplasmic characteristics, and nuclear-cytoplasmic ratio.
- The accuracy of cytologic diagnosis depends primarily on proper specimen collection, processing, and staining.
- Improper collection or delayed fixation can produce poor-quality smears and false diagnostic interpretation.
- Cytologic specimens may be collected from exfoliated cells, scraped surfaces, aspirated material, or body fluids.
- Fine-needle aspiration is one of the most commonly used methods for obtaining cellular material from palpable lesions.
- Immediate fixation is essential to preserve nuclear detail and prevent drying artifacts.
- Papanicolaou stain is the most important stain for routine cytologic examination because it provides excellent nuclear and cytoplasmic detail.
- Cytology is widely used in screening for Cervical Cancer and other cancers.
Types of Cytologic Specimens
Cytologic specimens are broadly divided into two major categories:
1. Exfoliative Cytology
This includes cells shed spontaneously from epithelial surfaces.
Examples include:
- Sputum
- Urine
- Pleural fluid
- Ascitic fluid
- Cerebrospinal fluid
- Vaginal smear
- Bronchial washings
These cells are naturally detached and collected for examination.
2. Interventional Cytology
Cells are obtained by active mechanical removal.
Examples include:
- Fine needle aspiration cytology (FNAC)
- Cervical scraping
- Endometrial aspiration
- Bronchial brushing
- Gastric brushing
Methods of Cytologic Specimen Collection
The methods used for collecting cytologic specimens depend on the source of cells and are broadly classified into:
- Exfoliative cytology
- Scraping and brushing techniques
- Fine needle aspiration cytology
- Fluid cytology
1. Exfoliative Cytologic Specimens
Exfoliative cytology involves collection of cells that are naturally shed from epithelial surfaces into body secretions or fluids.
Common Exfoliative Specimens
- Sputum
- Urine
- Pleural fluid
- Ascitic fluid
- Cerebrospinal fluid
Important Features
- Cells are collected without mechanical intervention
- It is a non-invasive method
- Useful for screening epithelial lesions
Clinical Importance
Exfoliative cytology is widely used in detecting inflammatory, infectious, and malignant lesions of internal organs.
2. Cervical Cytologic Specimen Collection
Cervical cytology is one of the most important applications of cytology for screening premalignant and malignant cervical lesions.
Cervical Cancer
Instruments Used
- Ayre spatula
- Endocervical brush
- Glass slide
- Speculum
- Fixative
- Patient is placed in lithotomy position
- Cervix is exposed using speculum
- Ayre spatula is rotated over transformation zone
- Material is spread evenly on glass slide
- Immediate fixation is performed
Importance
Immediate fixation prevents drying artifact and preserves nuclear morphology.
3. Brushing and Scraping Cytology
Mechanical removal of cells is performed when natural exfoliation is insufficient.
Common Sites
- Bronchus
- Gastrointestinal tract
- Endometrium
- Oral cavity
Procedure
- Brush or spatula is introduced into lesion area
- Surface cells are gently scraped or brushed
- Material is transferred onto slide
Uses
This method provides fresh representative cells from suspicious mucosal lesions.
4. Fine Needle Aspiration Cytology (FNAC)
Fine-needle aspiration
FNAC is an important method for collecting cells from palpable and deep-seated masses.
Common Sites
- Thyroid gland
- Breast lump
- Lymph node
- Salivary gland
- 22–24 gauge needle
- Syringe
- Syringe holder
- Glass slides
Procedure
- Lesion is immobilized
- Needle is inserted into lesion
- Negative pressure is applied
- Cellular material is aspirated
- Smears are prepared immediately
Advantages
- Simple
- Rapid
- Minimally invasive
- Cost effective
5. Body Fluid Cytology
Body fluids are important cytologic specimens for diagnosing inflammatory and malignant conditions.
Common Body Fluids
- Pleural fluid
- Ascitic fluid
- Pericardial fluid
- Cerebrospinal fluid
Pleural Effusion
Collection Method
- Fluid is aspirated under sterile conditions
- Collected in clean sterile container
- Sent immediately to laboratory
Importance
Body fluid cytology helps identify:
- Malignant cells
- Mesothelial cells
- Inflammatory cells
- Infectious agents
6. Sputum Cytology
Sputum cytology is useful in respiratory tract diagnosis.
Lung Cancer
Collection Method
- Early morning specimen preferred
- Patient performs deep cough
- Thick sputum collected in sterile container
It helps detect:
- Malignant bronchial cells
- Chronic inflammatory lesions
- Infectious organisms
7. Urine Cytology
Urine cytology is used to detect exfoliated cells from urinary tract lesions.
Bladder Cancer
Collection Method
- Fresh midstream urine collected
- Prefer second morning sample
Importance
Useful for detecting:
- Urothelial malignancy
- Inflammatory changes
- Cellular atypia
Processing of Cytologic Specimens
Initial Processing of Cytologic Specimens
Immediately after collection, specimens must be processed without delay because prolonged standing causes cellular degeneration.
Important Initial Steps
- Identification and labeling of specimen
- Gross examination of specimen
- Selection of suitable processing method
- Preparation of smear or sediment
Smear Preparation
Smear preparation is the first major laboratory procedure in cytology.
Characteristics of a Good Cytologic Smear
- Thin and uniform spread
- Adequate cellularity
- Minimal cell overlap
- No crushing artifact
- Proper background preservation
Methods of Smear Preparation
- Direct Smear Method – A small amount of material is directly spread on a glass slide.
- Pull-Apart Technique – Two slides are placed together and gently separated to distribute material evenly.
- Crush Smear Technique – Used when material is soft and semi-solid.
Fixation of Cytologic Specimens
Fixation is essential for preserving cellular details immediately after smear preparation.
Objectives of Fixation
- Prevent drying artifact
- Preserve nuclear chromatin
- Maintain cytoplasmic structure
- Prevent bacterial decomposition
Types of Fixation
Wet Fixation
Most commonly used for routine cytology.
Common Fixatives
- 95% ethanol
- Ether-alcohol mixture
Spray Fixation – Used when wet fixation is not immediately available.
Air Drying – Used for Romanowsky staining methods.
Processing of Fluid Cytology Specimens
Body fluids often contain fewer cells and therefore require concentration before smear preparation.
Common Fluids Processed
- Pleural fluid
- Ascitic fluid
- Pericardial fluid
- Cerebrospinal fluid
Pleural Effusion
Methods Used
Centrifugation
Most common concentration technique.
Procedure
- Fluid placed in centrifuge tube
- Centrifuged at appropriate speed
- Supernatant discarded
- Sediment used for smear preparation
Cytocentrifugation – Used when cellularity is very low.
Membrane Filtration – Used to collect scanty cells efficiently.
Cell Block Preparation
Cell block preparation converts cytologic sediment into paraffin-embedded material.
Advantages
- Preserves tissue architecture
- Allows special stains
- Useful for immunocytochemistry
Procedure
- Sediment fixed
- Embedded in paraffin
- Thin sections prepared
Staining of Cytologic Specimens
Staining is essential because unstained cells are transparent and difficult to evaluate microscopically. Cytologic stains provide contrast between nucleus, cytoplasm, and background elements.
Routine Cytologic Stains
1. Papanicolaou Stain
The most widely used stain in routine cytology.
- Hematoxylin for nucleus
- Orange G for keratinized cells
- EA stain for cytoplasm
Advantages
- Excellent nuclear detail
- Transparent cytoplasm
- Ideal for cancer screening
2. Giemsa Stain
Used mainly for air-dried smears.
Uses
- FNAC smears
- Blood-rich aspirates
- Bone marrow smears
Advantages
- Good cytoplasmic detail
- Better background clarity
3. Hematoxylin and Eosin Stain
Mainly used for cell block sections.
Features
- Nucleus stains blue
- Cytoplasm stains pink
Special Cytologic Stains
PAS Stain
Periodic acid–Schiff stain
Used for:
- Glycogen
- Mucin
- Fungi
Ziehl-Neelsen Stain
Ziehl–Neelsen stain
Used for acid-fast organisms.
Mounting of Cytologic Slides
Mounting is the final laboratory step after staining that preserves stained smears permanently.
Steps in Mounting
- Dehydration of stained slide
- Clearing in xylene
- Application of mounting medium
- Placement of coverslip
Mounting Medium Commonly Used
- DPX
Importance of Mounting
- Preserves stained smear
- Prevents fading
- Allows long-term storage
Quality Control in Cytology Laboratory
Quality control is essential to ensure reliable and reproducible cytologic diagnosis.
Important Quality Control Measures
- Correct specimen labeling
- Adequate specimen collection
- Immediate fixation
- Standard staining protocol
- Proper slide preservation
Pre-Analytical Quality Control
Includes all steps before staining.
Important Factors
- Correct patient identification
- Adequate specimen volume
- Proper transport conditions
Analytical Quality Control
Includes laboratory processing and staining.
Important Factors
- Correct stain preparation
- Controlled staining time
- Clean reagents
- Proper microscope calibration
Post-Analytical Quality Control
Includes reporting and documentation.
Important Factors
- Accurate reporting
- Slide review when necessary
- Record maintenance
Common Errors Affecting Quality
- Thick smear
- Poor fixation
- Overstaining
- Understaining
- Labeling errors