**Core Concept**
End-stage renal disease (ESRD) is a condition where the kidneys have lost nearly all their ability to function and filter waste from the blood. The glomerular filtration rate (GFR) is a key indicator of kidney function, and a specific threshold is used to define ESRD.

**Why the Correct Answer is Right**
The National Kidney Foundation defines ESRD as a GFR of less than 15 mL/min/1.73 m^2. This threshold is chosen because it indicates that the kidneys are no longer able to effectively remove waste products from the blood, leading to a buildup of toxins and electrolyte imbalances. The kidneys' inability to regulate fluid balance, acid-base status, and electrolyte levels also contributes to the development of ESRD.

**Why Each Wrong Option is Incorrect**
**Option A:** A GFR of 30 mL/min/1.73 m^2 is still within the range of chronic kidney disease (CKD) stages 3-4, where the kidneys are impaired but not yet at the point of ESRD.
**Option B:** A GFR of 15-29 mL/min/1.73 m^2 is also indicative of CKD, but the kidneys still retain some function and are not yet in the end-stage.
**Option D:** A GFR of 60 mL/min/1.73 m^2 is within the normal range, indicating healthy kidney function.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the GFR is affected by factors such as age, sex, and body size, and should be adjusted accordingly. The Cockcroft-Gault equation and the MDRD equation are commonly used to estimate GFR in clinical practice.

**Correct Answer: C. 15 mL/min/1.73 m^2**