A number of glucose (sugar) in the plasma (a fraction of the blood obtained by venous extraction) or for capillary puncture (in the finger) major than 140 milligrams for every 100 milliliters after eight hours of fasting and repeated in two different occasions, it is considered to be a diabetes mellitus and needs evaluation and treatment for a doctor.

Numbers between 110 and 140 are considered to be prediabetics and between 70 and 110, normal.

The values obtained in absence of fasting are very variable. The sugar determination in urine is less trustworthy, although, in general, the presence of sugar in ayunas urine confirms the diabetes, although his absence does not discard it.