Recognizing and differentiating uncommon body fluids: Considerations and tools for a proper practical approach

Clinical laboratories are regularly requested to inspect uncommon body fluids obtained from patients because clinicians are uncertain as to the origin of the collected material. They may need this information for the actual diagnosis, to confirm a supposition, or for guiding treatment and invasive operations like draining and puncturing. Often there is also a need to know more precisely what is going on in the cavity that gave rise to the fluid, for instance a local infection or metastasis, or whether the cavity is connected to organs or fluid compartments nearby etcetera. The results of the laboratory investigations often have () direct consequences. As the investigation of uncommon body fluids is distinct from routine laboratory analyses it requires special attention. This paper presents an overview of the characteristics of uncommon human body fluids, constituents useful as markers for recognizing and differentiating fluids and considerations that have to be taken into account when interpreting the results of analyses. In addition a number of practical recommendations for approaching the task of identifying uncommon body fluids are given.