What information should be included on a lab slip when ordering a sputum culture, including requests for sensitivity testing?

Ordering Sputum Culture: Essential Information and Reflex Sensitivity Testing

When ordering a sputum culture, the laboratory requisition form should include clinical diagnosis, suspected pathogens, current antibiotic therapy, and patient risk factors, with reflex antimicrobial susceptibility testing automatically performed on clinically significant isolates. 1

Required Information on Laboratory Requisition

Essential Clinical Information

• Clinical diagnosis (pneumonia, bronchitis, suspected TB, etc.)
• Suspected pathogens if applicable
• Current antibiotic therapy or recent antibiotic use
• Immunocompromised status if present
• Recent travel history (especially for Legionella testing)
• Risk factors for resistant organisms

Specimen Collection Details

• Date and time of collection
• Method of collection (expectorated, induced, bronchoscopy)
• Whether collected before or after antibiotic administration

Reflex Sensitivity Testing

Antimicrobial susceptibility testing is automatically performed (reflexed) on clinically significant isolates without requiring a separate order. This includes:

• Standard susceptibility panels for common respiratory pathogens
• Extended panels for resistant organisms or in immunocompromised patients
• Special testing for unusual pathogens when indicated

Quality Assessment Parameters

The laboratory will assess specimen quality using these criteria 1, 2:

• ≥25 polymorphonuclear leukocytes per low-power field
• <10 squamous epithelial cells per low-power field

Poor-quality specimens will be rejected with a comment indicating inadequate specimen quality.

Special Considerations

For Suspected Tuberculosis

• Specify "AFB culture and smear" on the requisition
• Three consecutive morning specimens are recommended 3
• Include request for molecular testing if available

For Suspected Atypical Pathogens

• For Legionella: Note "suspected Legionella" (requires special media)
• For Mycoplasma/Chlamydia: Standard cultures will not detect these organisms
• Consider requesting PCR testing for these pathogens 3

For Immunocompromised Patients

• Note immunocompromised status
• Consider requesting fungal cultures
• Request extended incubation if appropriate

Interpretation Guidelines

The laboratory report will typically include:

• Gram stain results
• Predominant organism(s) isolated
• Quantification of growth (light, moderate, heavy)
• Antimicrobial susceptibility results for significant pathogens

Common Pitfalls to Avoid

1. Specimen collection after antibiotic initiation: This significantly reduces diagnostic yield 1
2. Delayed transport: Specimens should reach the laboratory within 2 hours
3. Insufficient clinical information: Providing inadequate clinical details may lead to incomplete testing
4. Misinterpreting normal flora: Without proper quality assessment, oropharyngeal contamination may be misinterpreted as pathogens 2, 4

Remember that sputum cultures are most valuable when obtained before antibiotic administration and transported promptly to the laboratory. The quality of the specimen is crucial for accurate results, with purulent samples from deep coughing providing the most reliable information.