**Core Concept**
The **ELISA (Enzyme-Linked Immunosorbent Assay)** test and **Western blot** technique are both used for the diagnosis of **HIV (Human Immunodeficiency Virus)** infection, but they differ in their sensitivity, specificity, and purpose. ELISA is a screening test, while Western blot is a confirmatory test.

**Why the Correct Answer is Right**
ELISA is highly sensitive but may produce false-positive results, whereas Western blot is more specific and is used to confirm the diagnosis. Western blot detects the presence of specific **HIV antibodies** against various viral proteins, making it a more accurate test.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because ELISA is not more specific than Western blot.
**Option B:** Incorrect because Western blot is not less sensitive than ELISA for confirming HIV diagnosis.
**Option C:** Incorrect because ELISA is not used as a confirmatory test, but rather as a screening test.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that while ELISA is used for initial screening due to its high sensitivity, Western blot is used for confirmation due to its high specificity, reducing the risk of false positives.

**Correct Answer:** D. Less sensitive but more specific