External Quality Assessment Of AfB Smear Microscopy in Tuberculosis
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Date
2009-11
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Addis Ababa University
Abstract
Tuberculosis is the world's most serious infectious disease, with over 2 million deaths
each year. About a third of the world’s populations are latently infected with
Mycobacterium tuberculosis. More than 95% of tuberculosis cases and deaths occur in
resource-poor countries of the less-developed world. The diagnosis of tuberculosis
mostly relies on tuberculin skin test, chest radiography, culture, and smear microscopy.
Sputum smear microscopy is the most widely used technique for the diagnosis of
pulmonary TB (PTB) especially in high prevalence countries. For effective TB detection,
it is essential to assure the quality of smear microscopy. Quality Assurance (QA) is a
system designed to continuously improve the reliability and efficiency of laboratory
services. Panel testing, one of the QA systems that can provide data on laboratory
capabilities and assess the current status of laboratory performance and detect problems
associated with diagnostic performance. This study aims to prepare panel slides using
three different methods, evaluate the efficiency of AFB smear microscopy in different
laboratories in Ethiopia and the proficiency of peripheral laboratory technicians following
training. Until now panel slides have been prepared by two methods. The methods use
AFB appositive and negative sputum samples treated with sodium hydroxide (NaOH)
and N-acetyl- L-cysteine (NALC). The third procedure of preparation of sputum smear
slides for panel testing using new artificial sputum preparation method was developed
and examined using a cultured monocyte cell line, cultured avirulent mycobacteria and
methyl cellulose(MC) or polyacrylamide gel (PAM) for viscosity and background.
Since it is expensive and tedious to grow monocytes in the laboratory we used pus drawn
from acute abscesses in patients admitted to St. Paul hospital. Panel slides were prepared
using the above three methods and compared. Slides prepared using NaOH were
consistent with positivity grades but were not similar with real direct sputum smears
macroscopically or microscopically. But slides made using PAM and MC were consistent
with panel positivity grades and were similar to real direct sputum smears. Slides made
with the three methods were found as they can be used for EQA and training in
tuberculosis laboratories and microscopy centers. The slides were sent to 56 laboratories
in the country to assess the performance of laboratory technicians. The result shows that
the personnel were proficient enough to detect positive smears. A total of 29 technicians
were trained and tested. Their results show that there was definite improvement after
training. The results before training show that there is a high possibility of false
negativity as a result of low performance of laboratory technicians. So panel slides have
significant importance in assessing the performance of laboratory technicians and
evaluating their proficiency before and after training. Moreover since the efficiency of
lab technicians has significant effect on smear microscopy result, continuous external
quality assessment has to be conducted using methods like panel slides.
Key words: External quality assessment, panel test, validity, Mycobacterium tuberculosis
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Keywords
External quality, assessment, panel test, validity, Mycobacterium tuberculosis