Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of [[fibrinogen]] to [[fibrin]]. In the laboratory, it is used to distinguish between different types of [[Staphylococcus]] isolates. Importantly, S. aureus is generally coagulase-positive, meaning that coagulase negativity usually excludes S. aureus. However it is now known that not all S. aureus are coagulase-positive.

see [[Coagulase negative staphylococcus]].