Sputum Cytology
Sputum cytology examines cells coughed up from the lower airways for malignant cells, infection and inflammatory change. Cells are shed from the bronchial epithelium and from tumours that communicate with an airway.
It is a non-invasive, inexpensive test, and it was used widely in the past as a screen for lung cancer. Screening by sputum cytology has not reduced deaths, and low dose CT has replaced it for high risk smokers. Its present role is as a simple diagnostic test in patients who cannot undergo bronchoscopy, or where bronchoscopy and tissue biopsy are not available.
A good sample needs a deep cough that brings up material from the lower airway, and not saliva. Three early morning samples on consecutive days are collected. The report is available in 2 to 5 days.
Sensitivity is about 65 to 80% for central squamous cell carcinoma, and lower for adenocarcinoma and peripheral tumours, which do not shed cells into the airway. Overall sensitivity for lung cancer is about 40 to 60%, and specificity is over 95%. A negative result does not exclude cancer.
Indications.
- Suspected lung cancer when bronchoscopy or biopsy is not possible or is delayed (a central mass, haemoptysis, persistent cough in a smoker).
- Haemoptysis with a normal chest imaging in a person at high risk of central tumour.
- Lung mass in a patient unfit for invasive procedures.
- Suspected pulmonary infection when organisms such as fungi, Pneumocystis (limited sensitivity) and viral inclusions are sought.
- Evaluation of eosinophilic and asthmatic airway inflammation (eosinophils, Charcot-Leyden crystals, Curschmann spirals).
- Occupational lung disease (asbestos bodies, silica).
Not indicated as a lung cancer screening test for asymptomatic people. It is also not a substitute for acid fast microscopy, culture or molecular tests, which need their own samples.
Contraindications and precautions.
- Patient unable to cough up sputum, or an uncooperative patient: induced sputum with nebulised hypertonic saline, under supervision.
- Induced sputum causes bronchospasm in asthma, so a bronchodilator is given and spirometry is monitored.
- Active tuberculosis or suspected highly infectious disease: samples are collected in a ventilated space with respiratory protection for staff.
- Haemoptysis with unstable airway: acute management first.
Preparation and technique.
The patient rinses the mouth with water and brushes the teeth to reduce contamination, and removes dentures. Early morning, before eating, is best.
The patient takes several deep breaths and coughs deeply into a wide mouthed container. Saliva and nasal discharge are avoided. For an induced sample, a nebuliser delivers hypertonic saline for 10 to 20 minutes.
Three samples are collected on separate days. The sample is sent fresh to the laboratory without delay, or placed in an alcohol based fixative (equal volume of 50% alcohol with a wax) if transport is slow. The cytologist selects bloody or solid particles to prepare smears and cell blocks.
