Final answer:
Diabetes insipidus must be considered when a patient excretes large volumes of dilute urine accompanied by increasing serum osmolarity and electrolyte concentrations, which occurs due to underproduction of ADH or mutation in ADH receptor leading to poor water retention by the kidneys.
Step-by-step explanation:
If a patient voids large amounts of very dilute urine with an increasing serum osmolarity and electrolyte concentration, the condition to consider is diabetes insipidus. This condition is characterized by chronic underproduction of Antidiuretic Hormone (ADH) or a mutation in the ADH receptor. When the posterior pituitary does not release enough ADH, the kidneys cannot retain water, thus causing the production of large volumes of dilute urine. This results in increased thirst, and although fluid intake increases, it doesn't reduce blood solute concentrations because the kidneys continue to excrete large amounts of water due to insufficient ADH levels. In severe cases of diabetes insipidus, electrolyte imbalances can occur due to dehydration.