Coagulase Test
The coagulase test helps separate Staphylococcus aureus from many coagulase-negative staphylococci.
Core idea
Coagulase status changes clinical significance, reporting, and susceptibility expectations in many specimens.
Principle
Coagulase converts fibrinogen to fibrin. Slide methods detect bound coagulase/clumping factor; tube methods detect free coagulase.
Visual reactions
Coagulase Reading Table
| Method | Detects | Positive clue | Main caution |
|---|---|---|---|
| Slide coagulase | Bound coagulase or clumping factor | Rapid visible clumping | Autoagglutination can confuse the result |
| Tube coagulase | Free coagulase | Clot formation in plasma | Read at the correct time and follow lab policy |
| Latex agglutination | Clumping factor and/or protein A depending on kit | Agglutination reaction | Kit targets vary by manufacturer |
Basic workflow
- Confirm the isolate fits a Staphylococcus-like branch.
- Choose slide or tube method according to lab procedure.
- Use proper plasma reagent and controls.
- Read clumping or clot formation at the correct time.
- Resolve discordant or weak results with the required method.
How to read it
- Positive coagulase supports Staphylococcus aureus in the right context.
- Negative coagulase supports coagulase-negative staphylococci or related organisms.
- Some organisms can cause false positives or confusing clumping.
High-yield trapCommon mistakes
- Testing organisms before confirming the right branch.
- Overreading autoagglutination.
- Forgetting that specimen source affects significance.
ShortcutStudent shortcut
Coagulase is not just a reaction. It asks whether this Staph-like isolate may be S. aureus.