## **Core Concept**
The confirmatory tests for *Corynebacterium diphtheriae* involve identifying the bacteria's toxin-producing capability. This is crucial because not all strains of *C. diphtheriae* produce toxin, and the disease diphtheria is caused by the toxin. The tests help in confirming the diagnosis and guiding the treatment.

## **Why the Correct Answer is Right**
The correct answer, **Elek's test**, is a specific method used to detect the diphtheria toxin. It involves the precipitation of toxin-antitoxin complexes in an agar gel. A positive result confirms the presence of diphtheria toxin, which is essential for diagnosing *C. diphtheriae* infection. This test is specific because it directly detects the toxin, which is the virulence factor responsible for the disease.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although it might represent a type of test, it is not specified as a confirmatory test for *C. diphtheriae* toxin production.
- **Option B:** Similarly, this option lacks specificity as a confirmatory test for toxin production by *C. diphtheriae*.
- **Option D:** This option is also incorrect for the same reason; it does not specifically confirm toxin production.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **Elek's test** and **PCR (Polymerase Chain Reaction)** are used for confirming the toxin-producing capability of *C. diphtheriae*. However, in clinical practice, PCR is increasingly used for rapid diagnosis, but Elek's test remains a classic confirmatory method.

## **Correct Answer:** . **Elek's test**