## **Core Concept**
Chronic Renal Failure (CRF), also known as Chronic Kidney Disease (CKD), progresses through stages characterized by decreasing renal function. The signs and symptoms of CRF become apparent when the kidney function declines significantly. This is often quantified by the Glomerular Filtration Rate (GFR), which is a key indicator of kidney function.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the signs and symptoms of CRF become evident when the GFR falls below 25% of the normal value. At this stage, the kidneys are severely impaired and can no longer adequately perform their functions, such as waste removal, electrolyte balance, and fluid balance. This leads to the accumulation of toxins, electrolyte imbalances, and fluid overload, manifesting as symptoms like fatigue, edema, and electrolyte disturbances.

## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option suggests that symptoms appear at a GFR that is still within the normal range or mildly decreased, which is not accurate for the overt symptoms of CRF.
* **Option B:** - While some symptoms can start to appear in this range, significant and overt symptoms of CRF typically become more pronounced at a more advanced stage of renal deterioration.
* **Option D:** - This option implies that symptoms are only apparent when renal function is almost completely lost, which underestimates the sensitivity of clinical presentation to renal function decline.

## **Clinical Pearl / High-Yield Fact**
A crucial point to remember is that the progression of CKD is often divided into five stages based on GFR, and symptoms typically become more pronounced as the disease progresses to stages 4 and 5 (GFR < 30 mL/min/1.73m²). Early detection and management of CKD can delay progression to these symptomatic stages. ## **Correct Answer: C. 25%**