How to Order Sputum Culture
To properly order a sputum culture, collect a purulent sputum sample early in the morning before antibiotic administration, ensure it is a deep-cough specimen, and process it rapidly within a few hours of collection. 1
Specimen Collection Process
Patient Preparation
- Instruct the patient to:
- Rinse mouth with water before collection
- Take several deep breaths
- Cough deeply from the lungs (not throat clearing)
- Expectorate directly into a sterile container
Timing of Collection
- Early morning specimens yield the best results 1
- Collect before initiating antibiotic therapy 1
- For hospitalized patients with suspected pneumonia, collect 3 separate morning samples 1
Quality Assessment
- A good quality specimen should:
- Be purulent (containing mucus and pus)
- Contain <25 squamous epithelial cells per low-power field 2
- Have >25 polymorphonuclear leukocytes per low-power field
Laboratory Processing
Required Tests
- Gram stain and culture should be ordered together 1
- The Gram stain helps validate subsequent culture results 1
- Request quantitative or semiquantitative culture when possible 1
Special Considerations
- For tuberculosis suspicion, specify "AFB smear and culture" 1
- For Legionella suspicion, request culture on buffered charcoal yeast extract agar 1
Clinical Utility and Interpretation
When to Order
- For hospitalized patients with suspected pneumonia 1
- When drug-resistant bacteria are suspected 1
- When an organism not covered by usual empiric therapy is suspected 1
- For patients with severe pneumonia requiring ICU care 1
Limitations to Consider
- Only 14.4% of patients provide adequate sputum samples with a predominant morphotype 3
- Sputum culture yield varies widely (20% for outpatients to 90% for hospitalized patients) 1
- Contamination with upper respiratory flora can affect results 1
Common Pitfalls to Avoid
- Accepting poor quality specimens (containing primarily saliva)
- Delaying processing beyond a few hours after collection
- Ordering cultures after antibiotics have been started
- Failing to correlate culture results with Gram stain findings
- Not specifying special culture requirements for suspected pathogens
By following these guidelines, you can maximize the diagnostic yield of sputum cultures and provide valuable information for targeted antibiotic therapy, particularly for hospitalized patients with community-acquired pneumonia.