TUBERCULIN TEST (PPD)

Tuberculin test is used as a tool to screen for high risk patients susceptible to TB. It's done by intradermal injection of purified protein derivative of the M.tuberculosis (PPD is another name of the test) that enhances the cell-mediated immunity and results in both induration & erythema. The result of the test are recorded according to the diameter of induration after injection not erythema. The test is said to be positive (i.e. the patient is of a high risk to acquire TB) if the induration diameter is:

1- More than or equal to 5 mm in:

Persons who are close contacts to TB patients.

Persons with CXR suggestive of lung fibrosis.

Patients with HIV-AIDS.

Patients under immunsuppression: Chronic steroid therapy, Chemotherapy, Blood malignancy, Rheumatoid arthritis, Crohn's disease.

2-More than or equal to 10 mm in:

Immigrant persons from endemic areas.

Patients with Selicosis.

Patients with comorbid disorders: Diabetes Mellitus, COPD, Heart Failure, Renal Impairment... 

Health care workers: doctors, nurses, cleansing workers.

3-More than or equal to 15 mm in:

Normal individuals.

Negative test means the diameter of induration is less than 2 mm.

All patients with a positive PPD should have a CXR.

If the CXR is normal, so the patient may have 'latent' TB. The patient should receive a 9 months course of INH + Vit B6. If the CXR is abnormal, get 3 successive sputum samples if positive, give AntiTB medications (rifampicin, INH, Pyrizenamide, ETB for 2 months and then 4 months only with rifampicin and INH). If negative treat as latent TB.

Don't forget: Vit B6 is essential with INH to prevent peripheral neuropathy.