Mantoux Test: How to Read Correctly & Avoid Common Mistake (Video)

Transcript

5 mm vs 10 mm: which matters?

5 mm vs 10 mm: which matters?

Mantoux Test Basics

We’ll walk through reading the Mantoux test, from timing to the key cut-offs, and reveal the biggest mistake to skip.

How the test works

A nurse injects a tiny amount of purified TB protein just under the skin of your inner forearm. If your immune system has seen TB before, memory cells rush in over the next two to three days, making a firm, raised bump. If not, the skin stays flat.

Reading the bump

The hard, raised area you can feel with your fingertips is the induration. Redness around it, called erythema, doesn’t count. The reader gently runs a fingertip or a ballpoint pen from the outside toward the centre until it stops at the firm edge, then measures that distance in millimetres.

BCG vaccine effect

Many people in South Asia receive the BCG vaccine at birth. It can trigger a small induration because the vaccine uses a weakened cousin of the TB germ. That effect usually fades, so a big reaction in an adult vaccinated as a newborn often points to actual TB exposure.

When to see a doctor

A positive Mantoux alone doesn’t mean you need medication. If you have a persistent cough, night sweats, fever, or are losing weight, see a doctor. Blood in sputum or severe breathlessness requires immediate care.

After a positive result

The doctor will ask about cough, fever, night sweats and weight loss, listen to your lungs and usually order a chest X-ray. If you’re still coughing, a sputum test may follow. The outcome is either active TB, which needs full treatment, or latent infection, which may need preventive therapy.

The one mistake to avoid

The single biggest error is measuring the red halo instead of the hard induration. Only the firm, raised area counts for the millimetre measurement that determines whether the test is positive.

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Read the full guide

The full guide is on thecareonline.com. General information only, so check with your doctor for your own case.