How do you obtain a sputum sample from an adult or elderly patient with respiratory symptoms?

How to Obtain a Sputum Sample

Collect sputum by having the patient cough deeply from the chest after instructing them to rinse their mouth, ideally obtaining an early morning specimen of 5-10 mL volume; if the patient cannot produce sputum spontaneously, perform sputum induction using nebulized 3-7% hypertonic saline. 1, 2

Patient Preparation and Spontaneous Expectoration

• Instruct the patient to rinse their mouth with water before collection to reduce oral contamination 1, 2
• Have the patient take several deep breaths and cough deeply from the chest, not just clearing the throat 3
• Collect at least 3 specimens, with at least one early morning sample, as this timing provides the highest diagnostic yield 1, 2
• The optimal volume is 5-10 mL per specimen (minimum 3 mL) 2
• Collect specimens 8-24 hours apart when multiple samples are needed 2

Approximately 32-76% of adult patients with pneumonia can produce adequate spontaneous sputum, though this rate is lower in elderly patients who often cannot expectorate effectively. 3 In primary care settings, about one-third of patients can produce spontaneous sputum without induction. 4

Sputum Induction Protocol (When Spontaneous Expectoration Fails)

Sputum induction is the preferred method when patients cannot expectorate spontaneously, as it has equal or superior diagnostic yield to bronchoscopy (91-98% by smear, 99-100% by culture) at significantly lower cost and risk. 3, 1, 2

Technical Requirements:

• Use nebulized hypertonic saline (3-7% concentration) administered over 15-20 minutes 1, 2, 5
• Pre-treat with inhaled salbutamol to prevent bronchospasm 5
• Perform in a negative-pressure room with air expelled directly outside, away from windows and air intake vents 1
• Healthcare workers must wear protective respirators (N95 or equivalent) during the procedure 1

Patient Management During Induction:

• Supervise the patient throughout the procedure 1
• Have the patient spit saliva into one container before coughing sputum into another to reduce salivary contamination 6
• Keep the patient in the treatment room or outdoors until coughing subsides before returning to common areas 1
• In resource-limited settings without negative-pressure rooms, perform collection outdoors 1

The success rate of sputum induction is approximately 80%, and it can obtain acceptable specimens from roughly half of patients in primary care who cannot produce spontaneous sputum. 5, 4

Quality Assessment of Specimens

Screen all specimens microscopically before processing to ensure they represent lower respiratory secretions, not saliva. 3

Cytological Criteria for Acceptable Specimens:

• ≥25 polymorphonuclear cells per low-power field (100x) 3
• <10 squamous epithelial cells per low-power field 3
• Specimens not meeting these criteria should be rejected and recollection attempted 3

The presence of >10 squamous cells indicates significant oral contamination and renders the specimen invalid for microbiological interpretation. 3 Separating saliva from sputum during collection reduces squamous cell contamination from 47% to 34%. 6

Alternative Methods When Induction Fails

If sputum induction is unsuccessful or not feasible:

• Nasotracheal suctioning can be performed in patients unable to cooperate 3
• Endotracheal aspiration if the patient requires mechanical ventilation 3
• Flexible bronchoscopy with bronchoalveolar lavage (BAL) should be considered when noninvasive methods fail and there is high clinical suspicion of infection, though this is more invasive and costly 3, 2

Bronchoscopy is particularly indicated when alternative diagnoses need exclusion or when drug-resistant organisms are suspected, as delayed diagnosis significantly impacts outcomes. 3

Critical Pitfalls to Avoid

• Never rely on a negative AFB smear to exclude tuberculosis, as only 63% of culture-confirmed TB cases have positive smears 1, 2
• Do not accept specimens with excessive squamous cells (>10 per field), as they represent saliva contamination and yield unreliable results 3
• Elderly patients frequently cannot produce sputum even with induction; have a low threshold for bronchoscopy in this population when clinical suspicion is high 3
• Approximately 14% of confirmed pulmonary TB cases have negative cultures, so clinical suspicion must guide management regardless of laboratory results 1, 2
• In long-term care facilities, acceptable sputum is obtained in <30% of residents with pneumonia, and >50% of specimens fail cytological screening 3