The nurse is right. It is a PPD skin test for TB

infection. The result should be read between 48-72 hours after the PPD was injected into your superficial skin layer in your forearm. If after 48 hours, your skin test is negative (diameter5mm), you need to take a chest X-ray to show that you lung is normal.

Some people have done PPD before and have a positive PPD in the medical record. In that case, there is no need to do another PPD. A normal chest X-ray within 3 month is good enough for the doctor to say you are OK.

Hope this can help. Good luck.