Pentosuria is a condition where the sugar xylitol,[1] a pentose, presents in the urine in unusually high concentrations.

[1][3] L-Xylulose is a reducing sugar, so it may give false diagnosis of diabetes, as it is found in high concentrations in urine.

[5] Using phenyl pentosazone crystals, phloroglucin reaction, and absorption spectrum, pentose can be traced back as the reducing substance in urine, with those that have pentosuria.

The most widely studied is essential pentosuria, where a couple of grams of L-xylusol are released into a person's system daily.

[7] L-xylulose reductase, contained in red blood cells, is composed of both a major and minor isozyme.