Coagulase

Use:

Differentiates Staphylococcus aureus from other Staphylococcus species.

Sample type:

plasma

Precautions

Do not use citrated blood, as false-positive results can occur.

Interfering factors:

Methicillin resistant Staph. aureus have reduced clumping factor.

Do not shake or agitate the tube as this could break up the clot.

Some staphylococci strains produce fibrolysin after prolonged incubation at 35°C that can break up the clot resulting in false negative. Incubate the tube overnight at room temperature if you do not get a clot in 4 hours.

Some other rarely encountered staph species are also coagulase positive by the tube method.

Pre analytical errors:

Sample with Citrate

Non sterilized loop

Post errors:

Delayed report

Corrective action:

Don’t use citrated blood.

Sterile the loop.