How to Boost the Effects of Two Step PPDs

There were concerns from the rising cases of tuberculosis (TB) in the United States during the early 90’s, necessitating the strengthening of TB control measures by agencies such as the Center for Disease Control. The purified protein derivative (PPD) test, one of such measures, involves a tuberculin skin test and is the only method available that can ascertain the diagnosis of tuberculosis infection when there are no clinical symptoms present in a patient. It is possible to boost the effects of a two-step PPD test.

Things You'll Need

• Pen
• Ruler
• Syringe
• Injecting needle
• Purified protein derivative

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Instructions

• 1

  Inject 0.1 milliliters of 5 tuberculin units of purified protein derivative intradermally on the dorsal surface of the forearm. Planting of PPD should be done by a qualified physician, nurse practitioner or a registered nurse. Read the test results between 48 to 72 hours after administration, as lesser time than this might give invalid results. Read the PPD by observing the site of test for indurations described as an unusually hard and raised spot. Measure the amount of indurations on the site using a pen and placing it on the ruler and record the outcome in millimeters.

• 2

  Administer a second dose to any patients or employees whose initial test results are negative and they have not had consecutive negative PPD in 12 months. Give this test after one to three weeks since the first test, as this reduces the chances of boosted reactions that can give invalid test results and read the PPD after 48 to 72 hours.

• 3

  Interpret the test results as positive if the indurations are greater than 5 mm for households with close contact with an actively TB suffering person, HIV patients or people suspected of having clinical signs of TB. Interpret indurations greater than 10 mm as positive for high-risk persons from low-income populations, intravenous drug users, foreign persons from countries with high TB prevalence, the homeless, people with medical conditions associated with high TB risk, and people in institutions for long-term care, such as nursing homes.

• 4

  Ask the patient or employee if he has had a past history of Bacille Calmette-Guerin, a vaccination mostly given to children in many countries that experience high TB prevalence to avert childhood TB meningitis, as this prior vaccination with BCG might present problems with interpretation of the two-step results. Interpret the results from a person with prior history of BCG vaccination as those of a person who had not received the vaccination, because unless repeated doses of BCG are given annually, false-positives from BCG decline at 10 percent annually, thus the Center for Disease Control recommends that prior history of BCG vaccination be ignored during interpretation of tuberculin tests.

• 5

  Ask the patient if he has had any acute viral infections, poor nutrition status, immune-suppressive therapy, live viral vaccines and diseases that affect the lymphoid tissue, as they might lead to false-negative tuberculin test results. Store the tuberculin used during testing properly to avoid contamination or dilution and properly administer it intradermally to prevent false-negative results.