Tuberculosis classification

Tuberculosis classification system (US)

As of April 2000, the American clinical classification system for tuberculosis is based on the pathogenesis of the disease.
Health care providers should comply with local laws and regulations requiring the reporting of TB. All persons with class 3 or class 5 TB should be reported promptly to the local health department.

Class	Type	Description
0	No TB exposure Not infected	No history of exposure Negative reaction to tuberculin skin test
1	TB exposure No evidence of infection	History of exposure Negative reaction to tuberculin skin test
2	TB infection No disease	Positive reaction to tuberculin skin test Negative bacteriologic studies No clinical, bacteriologic, or radiographic evidence of TB
3	TB, clinically active	M. tuberculosis cultured Clinical, bacteriologic, or radiographic evidence of current disease
4	TB Not clinically active	History of episode of TB or Abnormal but stable radiographic findings Positive reaction to the tuberculin skin test Negative bacteriologic studies and No clinical or radiographic evidence of current disease
5	TB suspect	Diagnosis pending TB disease should be ruled in or out within 3 months

The U.S. Citizenship and Immigration Services has an additional TB classification for immigrants and refugees developed by the Centers for Disease Control and Prevention. The B notification program is an important screening strategy to identify new arrivals who have a high risk for TB.

Class	Description
-	No TB Classification
A	TB with positive sputum smear
B1	Overseas evidence of TB with negative sputum smear ; includes "old healed TB" and previously treated TB
B2	Latent TB Infection defined as tuberculin skin test ≥ 10 mm
B3	TB contact