Recognize the indications for Isoniazid prophylaxis in a patient with a newly positive skin test for tuberculosis.

Explanation:

PPD conversion is a change from a negative PPD within the past 2 years to a positive PPD and is associated with a risk >3% per year of developing active DISEASE thus once disease is ruled out the patient should be given INH for 9 months.

If non compliant then weekly therapy for 12 months.

A change by more than 5 mm of induration is considered significant (examiners frequently trick people by saying erythema which has no significance).

There are a few  other risk factors which are  also associated with a higher risk of developing the disease. If anyone has these risk factors he/she should also be treated with INH for 9 months.

Risk factors include:
Steroid ingestion >15 mg/day
Diabetes
Total gastrectomy in the past
IV  Illicit drug use
On dialysis
CXR with evidence of old tuberculosis (healed).

Children < 5 years age exposed to an infective case of TB should be treated too but for 3 months regardless of PPD result.

IF PREGNANT with risk factors-Treat.
Without risk factors-delay treatment until after delivery.

All HIV patients should be treated for 12 months if they are recent converters.