Which of the following is not a serological test for early diagnosis of syphilis?

Options

A. TPI
B. VDRL
C. Widal test
D. All of the above

Answer

To determine which of the following is not a serological test for the early diagnosis of syphilis, we need to analyze the options provided.

### Step-by-Step Solution:

1. **Understand Syphilis**:
- Syphilis is a sexually transmitted disease caused by the bacterium *Treponema pallidum*.
- It's important to know that syphilis can be diagnosed using several serological tests.

2. **Review the Options**:
- We need to evaluate each option to see if it is a recognized serological test for syphilis.

3. **Option 1: TPI (Treponema Pallidum Immobilization Test)**:
- This test involves mixing a serum sample with living *Treponema pallidum* and checking for immobilization.
- Since it is used to diagnose syphilis, this is a serological test.

4. **Option 2: VDRL (Venereal Disease Research Laboratory Test)**:
- The VDRL test is a blood test that detects antibodies to *Treponema pallidum*.
- This is also a recognized serological test for syphilis.

5. **Option 3: Vidal Test**:
- The Vidal test is used to diagnose typhoid fever (enteric fever), not syphilis.
- Therefore, this is not a serological test for syphilis.

6. **Option 4: All of the Above**:
- Since we have identified that both TPI and VDRL are serological tests for syphilis, this option is incorrect.

7. **Conclusion**:
- The correct answer is **Option 3: Vidal Test**, as it is not a serological test for the early diagnosis of syphilis.

### Summary:
The answer to the question is that the **Vidal test** is not a serological test for early diagnosis of syphilis.