What is the cause of PU/PD in chronic kidney disease?

In chronic kidney disease (CKD), the kidneys progressively lose their ability to concentrate urine due to nephron damage and reduced renal function. This impaired concentrating ability leads to an increased solute load within the renal tubules, which in turn causes osmotic diuresis. The kidneys are unable to reabsorb water effectively because they are overwhelmed by the solute concentration. As a result, the failure to appropriately absorb water leads to polyuria (excessive urination), which subsequently creates compensatory polydipsia (excessive thirst) as the body attempts to maintain hydration.

The other options do not accurately describe the primary mechanism behind PU/PD in CKD. In the case of excessive water retention, the kidneys are not retaining water effectively; rather, they are losing it due to their inability to concentrate urine. Hormonal imbalances due to adrenal dysfunction may impact water and electrolyte balance but are not the direct consequence of CKD itself. Autoimmune destruction of the renal tubules would lead to different types of renal issues, but the hallmark of CKD is more about the loss of function and less about direct autoimmune effects. Therefore, the correct answer—referring to osmotic diuresis—is the key factor in understanding PU/