**Question:** Triad of Renal colic, Swelling in loin which disappears after passing urine is called -

A. Acute Pyelonephritis
B. Ureteric Stone
C. Urolithiasis
D. Nephrolithiasis

**Core Concept:** The described triad of symptoms is commonly observed in patients suffering from kidney stones or urinary tract obstruction. These symptoms are related to the pathophysiology of renal colic, loin swelling, and relief after passing urine.

**Why the Correct Answer is Right:**

The correct answer, **D. Nephrolithiasis**, refers to the formation, migration, or passage of kidney stones. Kidney stones are mineral deposits that can obstruct the urinary tract, leading to the described triad of symptoms. When urine flows through the obstructed urinary tract, it creates a pressure gradient, which results in renal colic and loin swelling as the kidney tries to dilate to maintain blood flow. Once the obstruction is relieved, the pressure gradient decreases, causing the relief in symptoms.

**Why Each Wrong Option is Incorrect:**

A. **Acute Pyelonephritis (AP)** is an infection of the kidney, causing inflammation and pain but not swelling that resolves after passing urine. AP symptoms usually include fever, chills, and systemic signs of infection, not specifically the described triad.

B. **Ureteric Stone (US)** refers to a stone lodged in the ureter, causing the triad of symptoms. However, ureteric stones are not responsible for the described triad of symptoms as they are located in the ureter, not the kidney.

C. **Urolithiasis (UL)** is a broader term for kidney stones, but it does not specifically address the described triad of symptoms.

**Clinical Pearl:** A proper understanding of these symptoms and their correlation with kidney stones or ureteric obstruction is essential for medical professionals to accurately diagnose and manage patients presenting with these symptoms. A thorough history and physical examination, including the described triad of symptoms, are crucial components in the diagnostic process. A targeted imaging study, such as a renal ultrasound or CT scan, can confirm the presence of kidney stones and guide further management.