SETTING: Ntcheu District, Central Region of Malawi. OBJECTIVES: To assess
- the feasibility of introducing simple internal quality control procedures for acid-fast bacilli (AFB) microscopy for the diagnosis of tuberculosis
- the quality of the district sputum smear microscopy service.
DESIGN: A simple internal quality control system was piloted in which district laboratory staff assessed:
- specimen suitability,
- time between sputum submission and smear examination,
- smear preparation and staining,
Actual times for processing specimens were compared with recommended times. External quality validation was carried out. RESULTS: Of 4805 sputum specimens:
- documentation was complete in 95%,
- 93% reached the laboratory within 7 days of collection,
- 96% of smears were well prepared and stained,
- 97% concordance (96.4% smear-positive and 97.6% smear-negative) was demonstrated when 208 smears were re-examined by a second technician.
The aggregate index of reliability was 86%. The mean time spent on microscopic examination was 3.8 minutes, compared with the recommended time of 10 minutes. When all smears from 164 patients were assessed externally, 98.2% concordance (98.1% smear-positive and 98.2% smear-negative) was demonstrated. False smear-negative and smear-positive rates were less than 2% each. CONCLUSION: District laboratory staff were able to incorporate simple quality control procedures for AFB microscopy into their routine practice, resulting in a reliable service. The lessons learnt are widely relevant and potentially useful for implementation of a national quality assurance scheme.
The International Journal of Tuberculosis and Lung Disease (2002) Volume 6, Number 1, pp. 47-54.