Factors contributing to the degree of polyuria in a patient with poorly controlled diabetes mellitus.
Polyuria due to a glucose-induced osmotic diuresis is common in patients with hyperglycemia. This diuresis usually abates when the plasma glucose level approaches its renal threshold; the usual time course is less than 8 hours after commencing therapy. A 69-year-old man with non-insulin-dependent diabetes mellitus maintained hyperglycemia (540 mg/dL) and polyuria (4.7 L/24 hr) for 40 hours. Because there was no external supply of glucose, a balance study was conducted between the third and 40th hour after commencing treatment. In this interval, the overall concentration of glucose in the urine was less than 100 mmol/L and the urine osmolality was 378 mOsm/kg H2O. To evaluate the expected composition of the urine during a glucose-induced osmotic diuresis, urine was analyzed in normal rats infused with glucose plus urea and in untreated BB diabetic rats (plasma glucose and urea similar to that in our patient) as well as in 29 patients with hyperglycemia and polyuria. Glucose accounted for 60% of the urinary osmoles in rats and humans. Two subgroups of patients had a much lower urine glucose: one had an impaired concentrating ability (n = 6) and the other had an increased rate of renal glucose reabsorption (n = 5). In conclusion, in polyuria caused by hyperglycemia, the urine glucose should be 300 to 400 mmol/L with normal renal function. In the case we report, both the concentration of glucose and its excretion rate were much lower than expected with steady-state hyperglycemia (540 mg/dL) due to the high rate of excretion of NaCl, a concentrating defect, and excessive renal reabsorption of glucose.