Clinical Case Scenario
A 16-year-old male with a history of type 1 diabetes mellitus presented in the emergency department. His condition has worsened over the past 3 days. He reported extreme thirst and has been drinking large quantities of fluids and juice. His urine output was very high during this period, and on history taking, it was found out that he had not been compliant with his insulin regimen for the last month. His urine flow rate is measured at 12 mL/min in the emergency room using a uroflowmeter.
Despite excreting large quantities of glucose in the urine, her plasma glucose concentration remains unchanged over the observation period.
Wrong Answer: A. Low ADH levels can lead to excessive water excretion, resulting in dehydration and a decrease in blood pressure, which was not the case for us, as his effective arterial blood volume is not contracted on examination of his clinical parameters.
Wrong Answer: B. There is no significant increase in BUN, signifying no muscle breakdown.
Right Answer: C. This osmotic diuresis is due to glucosuria. The patient exhibited polyuria due to a glucose-induced osmotic diuresis, as indicated by a urine osmolality of 452 mOsmol/kg H₂O and a high osmole excretion rate. Polyuria may be caused by either osmotic diuresis or a low medullary interstitial osmolality as a result of medullary illness if the urine osmolality (UOsm) is larger than 300 mOsm/kg H₂O. The osmolar excretion rate should be computed in such a case by multiplying the urine flow rate by the urine osmolality in order to differentiate between these. In our case, the product of urinary osmolarity and urine flow rate yielded an osmole excretion rate of 5.42 mOsmol/min (normal is 0.6 mOsmol/min), signifying osmotic diuresis . A medullary concentrating deficiency may be taken into consideration if the osmolar excretion rate is noticeably decreased, particularly in those who consume large amounts of animal protein and salt, which is not our case. A variety of osmoles, such as organic compounds like mannitol, urea, glucose, or excess sodium chloride, can cause osmotic diuresis. The rise in plasma glucose level of 1270 mg/dL far exceeded the renal threshold for glucose reabsorption, resulting in significant glucosuria. His plasma glucose remained unchanged, implying a continued glucose influx. The most plausible source was a large volume of glucose retained in his stomach from juice, which contains glucose. This suggests rapid gastric emptying in this patient, despite hyperglycemia typically slowing that process.
Explaination Approach to Polyuria
Water Deprivation Test
Wrong Answer: D. The patient is not having any renal impairment, as his plasma creatinine was 0.7 mg/dl, which was within normal limits .
