**Core Concept**
The diagnosis of **hematuria** is based on the presence of red blood cells in the urine, which can be an indicator of various underlying conditions such as urinary tract infections, kidney stones, or more serious diseases like cancer. The minimum number of red blood cells per high power field (**HPF**) or per milliliter (**mL**) of urine is crucial for establishing this diagnosis.

**Why the Correct Answer is Right**
To diagnose **hematuria**, the presence of at least **3 red blood cells per high power field (HPF)** in a centrifuged urine specimen is often considered significant. This cutoff helps differentiate between contamination and actual pathological conditions. The exact number can vary slightly depending on the source, but **3 RBCs/HPF** is a commonly accepted threshold.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it suggests a lower threshold that might not accurately reflect pathological hematuria.
**Option B:** Similarly, this is too low and could lead to false positives due to contamination.
**Option D:** This option is also incorrect as it does not align with the commonly accepted criteria for diagnosing hematuria.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the diagnosis of hematuria should be confirmed by a repeat urine test to rule out transient causes or contamination.

**Correct Answer:** C. 3 Red Blood Cells/HPF