Answer
It is an indication of Diabetes Insipidus. However because his ADH levels is very low, then it is Central Diabetes Insipidus(CDI) or Neurologic Insipidus.
Generally diabetes insidpidus is a clinical disorder due to disruption of the body electrolyte fluid balance,leading to increase in solute potential of the blood, polyuria and polydipsia. it is caused by infections, tumors, trauma, autoimmune diseases to the pituitary gland .
Specifically Central Diabetes Insipidus (CDI) is due to lack of ADH production in the hypothalamus. Since ADH promotes water re-absorption at the kidneys to increase blood volume,when solute potential of the blood increases during Hypernatremia, lack of ADH leads to increase in blood solute potential, from production of larger quantity of diluted urine -polyuria, and therefore polydipsia(great thirst), which depletes the blood of fluids and therefore rise in solute potential.
The fact that the polyuria remains the same despite no intake for 4hrs,is due to lack of ADH and therefore failure to stimulate re-absorption of water at the collecting duct, thus as the kidney produces urine, this is coming out with no re-absorption of water back to the blood,Therefore large diluted urine will continuously be produced.
N<u>ote - the condition is related to diabetes mellitus because of the polyuria, symptoms, it has no other correlation with diabetes mellitus outside this.</u>
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