Blinded rechecking of sputum smears for acid-fast bacilli to ensure the quality and usefulness of restaining smears to assess false-positive errors.
METHODS
Microscopy Centres, Velliyur Tuberculosis Unit, Tiruvallur District, Tamil Nadu, India.


METHODS
Twelve microscopy centre laboratory technicians examined 41978 direct sputum smears for acid-fast bacilli. Senior Tuberculosis Laboratory Supervisors (STLS) checked all positive smears (4696) and 10% of negative smears (4776) in an unblinded fashion as per Revised National Tuberculosis Control Programme (RNTCP) guidelines. Ten per cent of the positive and negative slides and another 10% of unchecked negative slides were selected systematically for blinded rereading at the Tuberculosis Research Centre (TRC); 422 slides were reread without and with restaining.


RESULTS
Unblinded checking by STLS of the smears read by the laboratory technicians yielded 95 to 100% agreement. Blinded rereading at the TRC revealed that false-negative errors were greater among the laboratory technicians (2-7%) than the STLS (0-3%). Restaining and blinded rereading of slides reduced false-positive errors from 27% to 7%.


CONCLUSIONS
Blinded rereading at the reference centre facilitates assessment of laboratory technicians and STLS. Restaining before rereading the smears was found to be useful for precise estimation of false-positive errors.
Tuberculosis Research Centre (Indian Council of Medical Research), Chetput, Chennai, India. selvakumarn@hotmail.com
N
N
Selvakumar
E
E
Prabhakaran
F
F
Rahman
N A
NA
Chandu
S
S
Srinivasan
T
T
Santha
L S
LS
Chauhan
P R
PR
Narayanan
D004396:Coloring Agents; D005189:False Positive Reactions; D006801:Humans; D007753:Laboratories / Q000458:organization & administration / Q000592:standards; D011786:Quality Control; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000517:prevention & control
D004396:Coloring Agents