Storage of heat-fixed unstained sputum AFB smears for panel testing in a tuberculosis unit in South India.

To evaluate the suitability for panel testing of heat-fixed unstained sputum AFB smears stored for up to 10 months, panels of slides were prepared at the national laboratory and stored under ambient conditions. Every month, three slides were utilised for panel testing in each of 12 microscopy centres; 70 smears were checked in a blinded fashion after 10 months. Reading errors occurred in 15/360 slides used in panel testing and in 4/70 slides used in blinded checking. The quality and grading of heat-fixed unstained smears were unaffected for up to 10 months and were found suitable for panel testing.