How is the ppd skin test being measured?

My son got a negative x-ray but his PPD tested positive, doctor measured the rash that appeared on his forearm and it says 12mm.





A doctor friend told us the raised/elevated portion should be measured, but in my son%26#039;s case, the diameter of the rash was measured and not the elevated portion.





What is the correct way of measuring the rash to say it%26#039;s positive?


|||They test it differently - but that stupid test is miss-read so much. The best way to test for TB is a quantiferon blood test. However, they aren%26#039;t free.





Good news is he most likely has latent TB if he tested positive to the skin test and has no signs in the chest X-ray. Latent TB is not contagious, has no symptoms, and he will otherwise be 100% normal. Latent TB means he came in contact with the bacteria but his body walled off the attack; did not kill it. That is why he tested positive in the skin test. There is medication to kill the bacteria, but it is a pill, daily, for 9 months.





something like 1/4 people have latent TB and only 1/10 turn into active TB from there. People who have latent TB are at a higher risk than people who don%26#039;t, but still very low.





Latent TB isn%26#039;t dangerous unless the patient has some kind of disorder that lowers their immune system, such as the HIV infection.








But back to your question - people read the blister, not the rash.|||It is suppose to be the raised bump, NOT the red area. I have to get a test every year being in the health care business. Have had one for over 18 years.


http://www.ehow.com/how_2330328_read-tb-鈥?/a>


Skin tests should be read between 48 and 72 hours after the injection when the size of the induration is maximal. The health provider will look at the area of the PPD injection to see if any localized swelling has occured. In addition, the diameter of the induration will be measured and recorded in millimeters.|||the diamater of a raised portion is what should be measured, simple redness is not a positive test, but raised redness of %26gt;5mm is positive|||it should have been measured for the width and ht of it.Good luck