If a patient did the mantoux test and the patient has been suffering from HIV. What value indicates the TB infection in the patient?

Appeared in: NORCET -2 (shift-2)

Explanation

The Mantoux test, or Tuberculin Skin Test (TST), checks for a delayed-type hypersensitivity reaction to Purified Protein Derivative (PPD) from Mycobacterium tuberculosis.
In individuals with HIV, the immune system is suppressed, leading to a diminished ability to mount a strong skin reaction.
Due to this immunosuppression, a smaller area of induration (firm swelling) is considered a positive result.
According to established guidelines (CDC, WHO), an induration of 5 mm or more is classified as a positive TST result for people living with HIV.

Option B: A 7 mm induration is not a standard cutoff value for interpreting a Mantoux test in any risk group. Since it is greater than 5 mm, it would still be considered positive for an HIV patient, but 5 mm is the specific threshold value.
Option C: An 11 mm induration is well above the 5 mm threshold for an HIV-positive patient. While it indicates a positive result, the question asks for the minimum value that indicates infection. The 10 mm cutoff applies to individuals with moderate risk, not severely immunocompromised patients like those with HIV.
Option D: A 15 mm induration is the threshold for a positive test in individuals with no known risk factors for TB. It is highly unlikely that a severely immunocompromised patient would mount such a large reaction, and waiting for this size would lead to missed diagnoses.

Clinical Relevance

Nursing practice connection: Use the key finding related to Interpretation of Mantoux test (Tuberculin Skin Test) in immunocompromised patients to guide bedside assessment, documentation, and the next nursing action.
Correctly interpreting a Mantoux test in an HIV-positive individual is critical for early diagnosis and initiation of treatment for latent or active TB, which can prevent progression to severe disease and reduce mortality.
A misinterpretation (e.g., using a 10 mm or 15 mm cutoff) could lead to a false-negative result, delaying necessary prophylactic therapy and increasing the risk of TB reactivation.
What if the patient was a healthy 25-year-old student with no known comorbidities or risk factors? In that case, the threshold for a positive Mantoux test would be an induration of 15 mm or more.

How to Approach the Question

First, identify the key elements of the question: the diagnostic test (Mantoux test) and the patient's specific condition (HIV).
Recognize that HIV causes immunosuppression, which is a critical factor in interpreting immunological tests.
Recall the standard guidelines for interpreting the Mantoux test, which have different cutoffs based on risk factors.
Associate the highest risk category (severely immunocompromised) with the smallest induration size for a positive result.
Select the value that corresponds to the threshold for HIV-positive individuals, which is 5 mm.

Concept Tested & Keywords

Concept Tested: Interpretation of Mantoux test (Tuberculin Skin Test) in immunocompromised patients.
Stem keywords: Mantoux test, HIV, TB infection
Lead-in keywords: What value indicates
Clinical cues: Patient has HIV, which signifies an immunocompromised state.

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E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart B (pp 202-403 of 604) p. 25-27

E6 Medicine Harrison 22e Part 1 pp. 1442-1444, 1443-1445

Practise the full NORCET -2 (shift-2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.