Dose of Tuberculin in Mantoux test is:-
**Core Concept**
The Mantoux test, also known as the Tuberculin Skin Test (TST), is a diagnostic tool used to assess latent tuberculosis (TB) infection. The test involves injecting a small amount of purified protein derivative (PPD) tuberculin into the forearm, and the resulting skin reaction is measured after 48-72 hours. The dose of tuberculin used is crucial for accurate interpretation of the test results.
**Why the Correct Answer is Right**
The standard dose of tuberculin used in the Mantoux test is 5 tuberculin units (TU), which is equivalent to 0.1 mL of a 5 TU/mL solution. This dose is sufficient to induce a measurable skin reaction in individuals with latent TB infection, while minimizing the risk of false-positive reactions in individuals without TB exposure. The 5 TU dose is based on the concentration of tuberculin proteins, such as PPD-S (purified protein derivative from strain 5), which are derived from Mycobacterium tuberculosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the traditional dose of tuberculin used in the Mantoux test is not 1 TU. Using a lower dose would reduce the sensitivity of the test, leading to false-negative results.
**Option B:** This option is incorrect because the dose of tuberculin used in the Mantoux test is not 10 TU. Using a higher dose would increase the risk of false-positive reactions and may cause unnecessary anxiety or treatment for individuals without latent TB infection.
**Option C:** This option is incorrect because the dose of tuberculin used in the Mantoux test is not 0.5 TU. Using an even lower dose would further reduce the sensitivity of the test, leading to increased false-negative results.
**Clinical Pearl / High-Yield Fact**
When interpreting the Mantoux test results, it is essential to consider the individual's risk factors for TB exposure, such as immigration from high-prevalence countries, household contact with someone with active TB, or previous TB treatment. A positive result (induration ≥ 10 mm) in these high-risk individuals warrants further investigation and treatment.
**Correct Answer:** C. 5 TU.