Overview
Sputum culture is the lower-respiratory bacteriology pathway that combines specimen quality assessment with culture and selective identification of potentially significant isolates.
Classification
| Smear pattern | Adequacy cue | Typical next step |
|---|---|---|
| Many PMN, few SEC | More lower-airway-like | Culture/workup per SOP |
| Many SEC, few PMN | Saliva-like | Reject or qualify per local rules |
| Mixed oral flora only | Contamination likely | Limit ID; comment |
Morphologic Features
Gram stain quality screens count squamous epithelial cells and neutrophils (schemes vary). Predominant bacterial morphotype on an adequate smear can support later culture correlation.
Laboratory Characteristics
- Local sputum grading chart
- Respiratory media menu
- Organism workup/exclusion lists
- Inadequacy report comments
Reference Intervals
Numeric SEC/PMN cutoffs for rejection or processing, and lists of isolates to identify from sputum, are institutional, verify local SOP.
Clinical and Laboratory Significance
Adequate specimens with predominant plausible pathogens support pneumonia workups. Inadequate specimens should not drive extensive identification cascades by default.
Differential Considerations
Distinguish lower-airway pathogens from oropharyngeal colonizers and from colonizing yeast commonly seen in expectorated material.
Comparison Tables
Sputum significance cues
| Isolate pattern | Framing | Avoid |
|---|---|---|
| Heavy predominant pathogen + good smear | Higher significance | Ignoring smear quality |
| Light mixed oral flora + poor smear | Contamination/colonization | Full ID of every colony |
| Candida only on expectorated sputum | Often colonization | Assuming fungal pneumonia |
Classification Frameworks
Not applicable.
Laboratory Notes
- Hedge grading cutoffs and media menus as local
- No treatment or dosing language in respiratory reports
- Always state specimen quality when SOP requires
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
Common questions about using this Sputum foundational topics Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Sputum laboratory reference?
Sputum is a Foundational Topics entry in the LabPedia Medical Laboratory Library, written for Medical Laboratory Science reference lookup.
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