Which statement best differentiates a guide catheter from a diagnostic catheter?

• A. The inner lumen of a guide catheter is larger
• B. The outer diameter of the diagnostic catheter is larger
• C. They have the same core dimensions
• D. A diagnostic catheter has a larger inner lumen

Answer: (A)

The main idea is that the guiding catheter is designed to carry interventional devices, so it needs a larger inner lumen. This larger space allows passage and exchange of equipment such as guidewires, balloons, microcatheters, and stents while also enabling reliable contrast delivery. Diagnostic catheters, by contrast, are optimized for imaging and contrast injection, not for passing bulky devices, so their internal bore is smaller.

That’s why the statement about the inner lumen being larger in a guide catheter is the best differentiator. Outer diameter and other “core dimension” details aren’t the defining factor—it's the amount of space inside the catheter. The other options either misstate which catheter has the larger lumen or imply the same or opposite relationships, which aren’t correct given how these catheters are purpose-built.