Overview
Coagulase tests detect clumping factor (bound coagulase) and/or free coagulase that converts fibrinogen to fibrin.
Clinical Importance
Presumptively identify S. aureus in staphylococcal workups
Guide rapid clinical reporting before full MALDI-TOF confirmation in some workflows
Specimen Requirements
- Specimen: pure culture isolate (colony) from primary clinical culture
- Source: organism recovered on appropriate agar after incubation
- Handling: test fresh colonies within the timeframe validated by the method (typically 18–24 h cultures for many spot tests)
- Controls: run positive and negative control organisms per SOP/QC schedule
Analytical Method
Slide (bound) coagulase mixes colony with plasma and looks for rapid clumping. Tube (free) coagulase incubates organism in plasma and looks for clot formation. Latex agglutination kits detect clumping factor/protein A as alternatives. MALDI-TOF often supersedes classical coagulase for final ID.
Instruments Used
Automated analyzers
- Automated identification systems that incorporate equivalent biochemical reactions (VITEK 2, MicroScan, Phoenix)
- MALDI-TOF MS (often used instead of classical spot tests for species ID)
Manual methods
- Manual tube and spot biochemical tests with visual endpoint reading
Reference Values
Microbiology results are interpreted against organism identification, specimen quality, clinical context, and current CLSI and/or EUCAST interpretive criteria (including CLSI M100 for susceptibility where adopted). Reporting conventions and critical-notification lists are institution-defined; verify against the performing laboratory SOP and current guideline editions.
Qualitative: positive or negative. Some S. aureus strains may be slide-negative; tube coagulase or alternative methods resolve discrepancies.
Interpretation
Common Causes of Increased Results
- Positive; presumptive S. aureus pending confirmation per SOP
Common Causes of Decreased Results
- Negative; consistent with coagulase-negative staphylococci; confirm when clinical significance is high
Clinical Significance
- Staphylococcal colony workup
- Rapid blood-culture bottle follow-up algorithms (method-dependent)
Factors Affecting Results
Pre-analytical
- Testing mixed colonies
- Expired or improperly stored plasma reagent
Analytical
- Autoagglutination misread as positive
- Reading tube coagulase too early or too late
Post-analytical
- Reporting colonizers as pathogens without clinical/site correlation
- Wrong interpretive criteria (CLSI vs EUCAST; outdated breakpoints)
- Failure to notify critical positive cultures per institutional policy
Advantages and Limitations
Advantages
- Classic, rapid staphylococcal separator
Limitations
- Rare atypical S. aureus reactions
- Largely replaced by MALDI-TOF for definitive ID in many labs
Clinical Pearls
Slide-negative does not always mean not aureus; know when your SOP requires the tube or MALDI confirmation.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- Carroll KC, Pfaller MA, Landry ML, et al., eds. Manual of Clinical Microbiology. ASM Press (verify current edition).
- 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).
WHO Publications
- World Health Organization. Laboratory and diagnostic guidance relevant to clinical microbiology practice (verify current WHO publication for the method).
Frequently Asked Questions
Common questions about using this Coagulase Test laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Coagulase Test laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Coagulase Test. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Coagulase Test specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Coagulase Test. Confirm collection details against your laboratory protocol.
Where are Coagulase Test reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Coagulase Test results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Coagulase Test?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Coagulase Test?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Coagulase Test?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Medical Microbiology topic.
What are the clinical pearls for Coagulase Test?
See the Clinical Pearls section for concise laboratory practice notes associated with Coagulase Test. Apply pearls alongside institutional protocols.
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