## Core Concept
The Glomerular Filtration Rate (GFR) is a key indicator of kidney function, representing the rate at which fluid filtered by the glomeruli is passed into Bowman's capsule. It is influenced by factors such as blood pressure, blood flow to the kidneys, and the permeability of the glomerular capillaries. An increase in GFR indicates an increase in the kidney's filtration efficiency.

## Why the Correct Answer is Right
The correct answer, **C. Increased renal blood flow**, is right because an increase in renal blood flow directly leads to an increase in the hydrostatic pressure within the glomerular capillaries. This increased pressure enhances the filtration of fluid from the glomerular capillaries into Bowman's space, thereby increasing the GFR. This relationship is described by the Starling forces, where an increase in hydrostatic pressure favors filtration.

## Why Each Wrong Option is Incorrect
* **Option A:** Decreased oncotic pressure would actually increase GFR. Oncotic pressure opposes filtration; a decrease in it would reduce the opposition to filtration, thereby increasing GFR. So, this option is incorrect because it suggests a decrease in GFR.
* **Option B:** Increased Bowman's capsule hydrostatic pressure would decrease GFR. This is because an increase in the hydrostatic pressure in Bowman's capsule increases the pressure opposing filtration, thereby reducing the net filtration pressure and GFR.
* **Option D:** Afferent arteriolar constriction would decrease renal blood flow to the glomerulus, which would decrease the hydrostatic pressure within the glomerular capillaries and consequently decrease GFR.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the GFR can be estimated using the Cockcroft-Gault formula or the MDRD (Modification of Diet in Renal Disease) equation, which take into account factors like serum creatinine, age, sex, and weight. An increase in GFR is not typically a concern but a high or increasing GFR can indicate hyperfiltration as seen in early diabetes.

## Correct Answer: C. Increased renal blood flow