During an assessment of the costovertebral angle, a normal percussion result yields which sound?

• A. Flat
• B. Dull
• C. Hyperresonance
• D. Tympany

Answer: (B)

The main idea is that percussion over the costovertebral angle assesses the kidneys. A normal finding in this area is a dull sound, because the kidney is a solid organ beneath the back muscles and ribs, which dampens the tapping. Other percussion sounds reflect different underlying contents: a harsh, air-filled bowel or lung area can produce tympany or resonance, while very dense structures like bone yield a flat tone. So dullness over the costovertebral angle fits with the expected renal tissue beneath, whereas hearing something like tympany, hyperresonance, or a flat sound would suggest other structures or conditions.