**Core Concept:**
Urinary tract infections (UTIs) are infections that occur in the urinary tract, including the kidneys, ureters, bladder, and urethra. In clinical practice, distinguishing between bacterial and non-bacterial causes of pyuria (pus cells) in urine is essential for guiding appropriate treatment.

**Why the Correct Answer is Right:**
For a UTI patient with pus cells but no visible organisms on urine examination, the correct answer is **Option C: Urine culture and sensitivity**. This is because a urine culture and sensitivity test is the most appropriate method to identify the causative microorganism(s) responsible for the pyuria. This test involves culturing urine to grow bacteria and determining their susceptibility to antibiotics.

**Why Each Wrong Option is Incorrect:**
Option A (urine antigen test) is not reliable for pyuria, as it detects bacterial antigens rather than culturing bacteria. Option B (urine microscopy) is limited in identifying the causative microorganism(s) without further testing. Option D (urine culture without sensitivity) would not account for the patient's antibiotic sensitivity profile, making the treatment less effective.

**Why the Correct Answer is Right:**
Urine culture and sensitivity is crucial in such cases because it directly identifies the causative microorganism(s) and enables appropriate antibiotic selection based on the organism's sensitivity profile, ensuring optimal treatment.

**Clinical Pearl:**
In cases of suspected UTI, conducting a urine culture and sensitivity test allows for targeted antibiotic therapy, minimizing the risk of antibiotic resistance and improving patient outcomes.