## **Core Concept**
The Enzyme-Linked Immunosorbent Assay (ELISA) and Western Blot are both laboratory techniques used to detect specific antibodies or antigens in a sample. ELISA is a rapid, sensitive test often used for initial screening, while Western Blot is a more specific confirmatory test. The key difference lies in their ability to provide information about the molecular weight of the antigens.

## **Why the Correct Answer is Right**
ELISA is considered **less specific** but **more sensitive** compared to Western Blot. This is because ELISA can detect antibodies or antigens with high sensitivity but may produce false-positive results due to non-specific binding. Western Blot, on the other hand, separates proteins by size (using SDS-PAGE) before detecting specific antibodies or antigens, making it more specific. Therefore, ELISA is often used as a screening tool, and Western Blot is used as a confirmatory test.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests ELISA is more specific than Western Blot, which is incorrect. Western Blot's ability to separate proteins by size before detection makes it more specific.
- **Option B:** This option implies both tests have equal sensitivity and specificity, which is not accurate. Western Blot is generally more specific than ELISA.
- **Option C:** This option states ELISA is more sensitive but less specific than Western Blot, which aligns with the characteristics of both tests but is not provided as an option to choose from in the context of selecting the best description.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that when screening for diseases like HIV, an initial positive ELISA result is typically followed by a more specific Western Blot test to confirm the diagnosis. This two-step approach helps minimize false positives.

## **Correct Answer:** C. More sensitive but less specific.