In diabetes mellitus, glucose appears in the urine because a
hyperglycemia condition exists in the blood. Therefore, the
glucose concentration should also be measured in the blood.
Glucosuria can occur temporarily from emotional stress or pain,
hyperthyroidism, alimentary hyperglycemia, and meningitis.
Apparently, the kidney acts as a safety valve against the
excessive accumulation of glucose in the blood. If the glucose
level becomes too high, then the renal threshold in the kidneys
may be exceeded. The renal threshold is a concentration level
above which all glucose is not reabsorbed in the blood, but the
excess above the threshold concentration remains in the urine. A
threshold is analogous to a dam and only when the water level
becomes too high, does the water spill over the dam. Many other
substances in the blood have their own threshold levels and when
the threshold is exceeded, the substance appears in the urine.
In renal diabetes, the threshold is abnormally low and glucose
appears in the urine at a m