**Core Concept**
Tuberculosis (TB) of the kidney, also known as genitourinary TB, is a type of extrapulmonary TB that affects the urinary tract. The kidney is the most common site of genitourinary TB, often resulting from the hematogenous spread of TB bacilli from a primary pulmonary focus.

**Why the Correct Answer is Right**
The earliest and often the only presentation of TB kidney is hematuria, which is the presence of blood in the urine. This occurs due to the inflammation and scarring of the renal parenchyma, leading to the destruction of the renal epithelium and the formation of blood clots. Hematuria can be microscopic or gross, and it may be accompanied by other symptoms such as flank pain, dysuria, or frequency.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fever is a non-specific symptom that can be associated with various conditions, including TB kidney, but it is not the earliest or most specific presentation.
* **Option B:** Proteinuria may occur in TB kidney, particularly if there is significant renal damage, but it is not the earliest or most characteristic presentation.
* **Option C:** Pyuria is the presence of white blood cells in the urine, which can be seen in TB kidney due to the inflammation and infection of the renal parenchyma. However, it is not the earliest or most specific presentation.

**Clinical Pearl / High-Yield Fact**
Remember that hematuria is a key feature of TB kidney, and it may be the only presentation in some cases. A high index of suspicion is necessary to diagnose TB kidney, particularly in patients with a history of TB exposure or from endemic areas.

**Correct Answer: C. Pyuria is a common finding in TB kidney but the earliest and often the only presentation is hematuria.**