Sweat as a clinical sample: what is done and what should be done.

Abstract

Sweat is known for being a clear, hypotonicbiofluid produced by eccrine and procrineglands located in the epidermis, with aslightly acidic pH (between 4.0 and 6.8), andcomposed mainly by water (99%), contain-ing the so-called electrolytes (e.g., sodium,chloride and potassium), urea, pyruvate andlactate; but also proteins, peptides, amines,amino acids and metal ions in smaller con-centrations, together with inhibitors, anti-gens, antibodies and a variety of xenobioticssuch as drugs, cosmetics and ethanol [1]. Theclinical importance of sweat has traditionallybeen limited to the determination of chlo-ride for the diagnosis of cystic fibrosis (CF)and incipient determination of drugs [1]. Thepresent spread of ‘omics’ disciplines, and par-ticularly of metabolomics as the youngestof the big ‘omics,’ has open a fan of possi-bilities to the use of sweat as clinical sample.Except for the case of some high molecularweight proteins, which reach sweat by dif-ferent intracellular storages in particularsituations [2,3], most sweat components aresmall molecules resulting from metabolicpathways; therefore, their study pertains tothe metabolomics field, the omics of smallmolecules typically (<1000 Da or <1500 Da).