Mannitol is a diuretic and renal diagnostic aid related to sorbitol. It has little significant energy value as it is largely eliminated from the body before any metabolism can take place. It can be used to treat oliguria associated with kidney failure or other manifestations of inadequate renal function and has been used for determination of glomerular filtration rate. Mannitol is also commonly used as a research tool in cell biological studies, usually to control osmolarity. Chemically, mannitol is an alcohol and a sugar, or a polyol; it is similar to xylitol or sorbitol. However, mannitol has a tendency to lose a hydrogen ion in aqueous solutions, which causes the solution to become acidic. For this, it is not uncommon to add a substance to adjust its pH, such as sodium bicarbonate. Mannitol is a non-permeating molecule i.e. it cannot cross biological membranes. Mannitol or hexan-1,2,3,4,5,6-hexol (C6H8(OH)6) is an osmotic diuretic agent and a weak renal vasodilator. It is a sorbitol isomer. Mannitol is found to be associated with cytochrome c oxidase deficiency and ribose-5-phosphate isomerase deficiency, which are inborn errors of metabolism. Mannitol is also a microbial metabolite found in Aspergillus, Candida, Clostridium, Gluconobacter, Lactobacillus, Lactococcus, Leuconostoc, Pseudomonas, Rhodobacteraceae, Saccharomyces, Streptococcus, Torulaspora and Zymomonas.