Okay, let's tackle this question. The patient is a 60-year-old smoker with painless gross hematuria. The key here is to figure out the most logical investigation. First, I need to recall the differential diagnoses for painless hematuria. Smokers are at higher risk for certain conditions, especially bladder cancer.

Painless hematuria is a red flag for urological malignancies, like bladder or renal cancer. Since the patient is a smoker, bladder cancer comes to mind. The most common presentation of bladder cancer is painless, intermittent hematuria. So the next step would be to investigate for bladder tumors. The standard imaging for this would be a CT urogram. It's better than an IVU because it provides cross-sectional images and can detect smaller lesions.

Other options might include cystoscopy, but that's more of a definitive test after imaging. Urine cytology is also used but might not be the first step. Renal ultrasound might be considered for kidney stones, but since the hematuria is gross and painless, stones are less likely. So the correct answer is CT urogram. Let me make sure I didn't mix up the options. The options were A to D, but the correct answer is CT urogram. The other options are less appropriate. Need to explain why each is wrong.

**Core Concept:** Painless gross hematuria in an elderly smoker is a classic presentation of urothelial carcinoma (bladder cancer). The gold standard investigation combines imaging and anatomical assessment to detect tumors, stones, or structural abnormalities.

**Why the Correct Answer is Right:** CT urogram is the preferred investigation because it provides high-resolution cross-sectional imaging of the entire urinary tract (kidneys, ureters, bladder), detects urothelial tumors, and evaluates for secondary causes like stones or obstruction. It outperforms conventional intravenous pyelogram (IVP) by offering multiplanar reformats and better sensitivity for small lesions.

**Why Each Wrong Option is Incorrect:**
**Option A:** Renal ultrasound may miss bladder lesions and lacks the detail to assess ureters.
**Option B:** Urine cytology is less sensitive for low-grade tumors and does not evaluate anatomy.
**Option C:** Cystoscopy is invasive and typically reserved for diagnostic confirmation after imaging, not the initial step.

**Clinical Pearl:** Remember the "3 Ds" for hematuria: *Dehydration, Drugs (e.g., NSAIDs), and Disease (malignancy, stones).* Painless hematuria in smokers demands urgent CT urogram.

**Correct Answer: C. CT urogram**

✓ Correct Answer: D. Urine microscopy for malignant cytology