The test is then read 48 to 72 hours later by measuring the size of the largest papule or induration.

Purified protein derivative (PPD) tuberculin is a precipitate of non-species-specific molecules obtained from filtrates of sterilized, concentrated cultures.

[citation needed] A batch of PPD created in 1939 serves as the US and international standard, called PPD-S.[4] PPD-S concentration is not standardized for multiple-puncture techniques, and should be designed for the specific multiple-puncture system.

[5] The American Thoracic Society or Centers for Disease Control and Prevention (CDC) do not recommend the tine test, since the amount of tuberculin that enters the skin cannot be measured.

[7][8] If a minor reaction is considered doubtful, the OT test is less accurate and may fail to detect TB, producing a false negative.