TB Skin Test
Difference between TB Class 2 and Class 4
TB treatment
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TB Skin Test
“Initial” test for “latent” tuberculosis infection (LTBI) is usually skin test. Montoux (PPD) is not the same as “2-step PPD”
Montoux Test (PPD) – is used as it is “cost effective” – injection of 5 tuberculin unit (0.1 ml) of purified protein delivative (PPD).
Chest X-ray – Chest X-ray is NOT definitive test for latent TB. Class 4=positive.
Interferon Gamma Release Assays (IGRAs) – costly, so it is NOT the “initial” test.
2-Step PPD – Montoux (PPD) x2 times (3週間後に再検査、とか）
Difference between TB Class 2 and Class 4
| TB Class | Class 2 | Class 4 | Class 3 |
| Skin Test | Positive | Positive | Positive |
| Chest X-Ray | Normal | Abnormal | Abnormal |
| IGRA Blood Test | Positive | Positive | Positive |
| S/S | No | No | Yes |
| Sputum | No Test | Negative | Often Positive |
| Contageous | No | No | Yes |
Class 1 = Exposured, but No s/s. Negative TB test.
Class 4 = Positive Chest X-ray due to past positive TB (tissue is not the same)
TB treatment
Class 2 = INH QD x9 months
Class 3,4,5 = Multi-drug Tx.
Class 5 (Dx = pending) のTxは3か月以上続けない = Dxをはっきりさせて、Tx内容を変更する。