Tuberculin Skin Test
1,550 Kshs | Home Collection Available
Synonyms
None
Purpose
Healthcare providers perform the Tuberculin Skin Test (TST) by injecting a small amount of tuberculin under the skin to detect exposure to Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB).
The healthcare provider injects a small amount of tuberculin purified protein derivative (PPD) just under the skin, typically on the forearm. After 48 to 72 hours, a healthcare provider checks the injection site for a reaction.
This test is important for identifying latent or active TB infections, especially in individuals with TB risk factors, such as healthcare workers, people with weakened immune systems, or those who have been in contact with TB patients. It plays a crucial role in TB screening programs, particularly in regions where the disease is prevalent.
The test can be done alongside Interferon-Gamma Release Assays (IGRAs), Chest X-ray, and Sputum Culture or Smear.
Patient Preparation
No special preparation needed
Samples
0.1 mL Tuberculin purified protein derivative (PPD) injection solution.
Reference Range
<5mm for people living with hiv, immunocompromised individuals, people who had contact with a recent TB infection, organ transplants, chest x-ray findings suggestive of previous TB disease. < 10mm for people within high TB prevalence countries, drug abusers, mycobacteriology laboratory workers, and people with certain medical conditions.
<15mm for people with no known TB risk conditions.
Results Turnaround
48 and 72 hours after administration of PPD.
Diseases / Diagnostic Indicators
A positive reaction to the Tuberculin Skin Test indicates that the person has been infected with Mycobacterium tuberculosis. This could mean a latent TB infection (where the bacteria are present but inactive) or an active TB disease.
The healthcare provider determines whether the result is positive by measuring the size of the induration (swelling) at the injection site, based on the individual’s health status and risk factors.
Common signs associated with active TB disease include:
- Persistent or prolonged cough (lasting 3 weeks or more)
- Chest pain or discomfort while breathing or coughing
- Unexplained weight loss
- Fatigue and weakness
- Fever and chills
- Night sweats
- Loss of appetite
A negative test result generally suggests that the person has not been infected with TB bacteria. However, false negatives may occur in individuals with weakened immune systems or recent TB exposure. Additional testing, such as IGRAs or chest imaging, may be required to confirm the diagnosis.
For more on skin tests, read this study.