# Mantoux Test (Tuberculin Skin Test)

## Overview

This module describes how to interpret a Mantoux test. Although often associated with false negatives and positives, the Mantoux test is part of the workup for suspected TB.

## Indications

1. Suspected TB infection in children under 5 years

## Contraindications

1. None

## Patient information & consent

### How do I explain this procedure?

“After we gave your child the injection to test for TB, we asked you to wait 2-3 days and then come back so that we can read the result.”

### What can my patient expect?

“I am going to measure with a ruler how large the spot on your child’s arm is. It will not hurt at all. From this I will be able to tell you if your child has TB or needs further testing for TB.”

### What is my patient’s role?

“Please hold your child’s arm steady for me while I measure.”

## Procedure

Follow medical asepsis without gloves.

1. Perform hand hygiene.

2. Ensure that the patient has returned 48-72 hours after injection.

3. Inspect the injection site under good light. You may see an area of erythema (redness), and usually a central raised area (induration).

4. Palpate the site to find the edges of the induration.

   Mark the edges
   Mark the edges

   Run the pen from outside the edge of the lesion inwards towards the inside of the lesion. This way you will feel when your pen brushes against the induration.

   of the indurated area with a pen.

5. Use a ruler
   Use a ruler

   A transparent ruler works best. If no ruler is available, use a tape measure.

   to measure across the indurated area.

6. Document the length across the induration.

## Interpretation

When is a Mantoux test positive?

- Induration ≥ 5 mm is positive in HIV positive, malnourished, or severely ill children.
- Induration ≥ 10 mm is positive in all children.

What does a positive test result mean?

- A positive result combined with a history of TB symptoms, a TB contact or a suggestive chest X-ray, indicates active TB disease and requires treatment.
- A positive result without any of the above may indicate latent TB infection. These patients should receive TB prophylaxis.

A false positive may occur if:

1. The patient is infected with non-tuberculosis mycobacteria

2. The patient has had the BCG vaccination

3. The patient has had previous, treated TB

4. The test was incorrectly performed or read

What does a negative test result mean?

- A negative result does not rule out latent TB infection or active TB disease.
- In suggestive cases with a negative Tuberculin Skin Test result, you may still need to do further TB workup (often some combination of a chest X-ray, gastric washings, sputum collection, and/or abdominal ultrasound) and you may also repeat the Tuberculin Skin Test after 8 weeks.

A false negative may occur if:

1. The patient has HIV, malnutrition, or is otherwise immunosuppressed

2. The patient only very recently got TB (8-10 weeks ago)

3. The patient is less than 6 months old

4. The patient had a live-virus vaccination in the past month

5. The patient has a severe viral infection (e.g. measles, chickenpox)

6. The patient has severe disseminated TB

7. The patient has had TB infection for years

## Troubleshooting

The patient presented too early to read the test.

Advise the patient to return in the 48-72 hour window. The results cannot be read yet.

The patient presented too late to read the test.

Schedule a repeat test as soon as possible (you may do it on the same day).

The patient is due for a live-virus vaccine and needs a TB test.

Do the test and administer the vaccine on the same day, or administer the vaccine now and perform the TB test a month later.

## References

1. Centers for Disease Control & Prevention. Tuberculin Skin Testing. September 2020. Available from: https://www.cdc.gov/tb/publications/factsheets/testing/skintesting.pdf

2. Pillay K. Tuberculin Skin Testing. 2015. Available from: http://www.lancet.co.za/wp-content/uploads/2015/07/South-Africa-Tuberculin-Skin-Testing-APR2015.pdf

3. Guidance for National Tuberculosis Programmes on the Management of Tuberculosis in Children. 2nd edition. Geneva: World Health Organization; 2014. Annex 3, Administering, reading and interpreting a tuberculin skin test. Available from: https://www.ncbi.nlm.nih.gov/books/NBK214439/