**Core Concept**
Glomerular injury can lead to the presence of abnormal cells or proteins in the urine, which can serve as diagnostic markers. Dysmorphic red blood cells (RBCs) are a hallmark of glomerular damage, where the normal filteration process is disrupted.

**Why the Correct Answer is Right**
The presence of 20% dysmorphic RBCs in the urine is a strong indicator of glomerular injury. Dysmorphic RBCs are shaped irregularly due to the glomerular injury, which disrupts the normal flow of blood through the glomeruli. This results in the RBCs being deformed as they pass through the damaged glomeruli, leading to their characteristic shape. The percentage of dysmorphic RBCs is a good indicator of the extent of glomerular damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Bright red cells are more indicative of lower urinary tract issues, such as bleeding from the urethra or bladder, rather than glomerular injury.

**Option C:** The presence of 100 RBCs per high power field is a significant finding, but it is not specific to glomerular injury. It can be seen in various conditions, including pyelonephritis, renal papillary necrosis, and other causes of hematuria.

**Option D:** Beta 2 microglobulin is a protein that is normally present in the urine in small amounts. Its presence in higher amounts can indicate tubular damage rather than glomerular injury.

**Clinical Pearl / High-Yield Fact**
Dysmorphic RBCs are a key finding in glomerular injury, and their presence can help distinguish glomerulonephritis from other causes of hematuria. The percentage of dysmorphic RBCs can also help estimate the severity of glomerular damage.

✓ Correct Answer: B. 20% dysmorphic RBC's