Table 1.

Biospecimen sources for application of metabolomics in TBI research

Biospecimen	Pros	Cons
Tissue	The most direct relevance to the injury, can compare injured hemisphere to uninjured hemisphere	Not applicable to clinical research; rarely would tissue be available and unclear how a metabolomics study could be designed
Blood	Easily obtained	Systemic vs. Brain
Arteriovenous differences	Systemic minus cerebral metabolites	Jugular catheter is invasive
Cerebrospinal fluid	Drained as a treatment for high intracranial pressure, would otherwise be discarded	Commonly available with severe injuries; invasive to obtain otherwise
Urine	Easily obtained	Concentration of metabolites a function of systemic dilution; within sample normalization is common
Cerebral microdialysate	From the cerebral tissue, as close to the source as possible	Low volumes obtained leading to pooling biofluid over a large periods of time; perfusate and not directly sampling extracellular fluid