During a tuberculosis screening program, a patient shows significant induration 48 hours after receiving a tuberculin skin test. The clinician explains that this result alone cannot confirm active tuberculosis. Why is additional testing necessary?

The skin test detects the presence of circulating tuberculosis bacteria but cannot measure their concentration

The reaction only shows immune sensitization to TB antigens and cannot distinguish between past exposure, vaccination, or active infection

The skin reaction measures antibody levels that fluctuate too rapidly to indicate disease status

The swelling occurs because the injected proteins damage local tissue rather than stimulate immunity