Random blinded rechecking of AFB smears in a pilot project at an intermediate reference laboratory

Area of Science:

• Medical Diagnostics
• Public Health Microbiology
• Tuberculosis Research

Background:

• Sputum smear microscopy is the primary diagnostic tool for tuberculosis (TB) in developing nations.
• Ensuring the quality of smear microscopy is vital for accurate TB diagnosis and patient management.
• The Revised National Tuberculosis Control Programme (RNTCP) relies heavily on microscopy services.

Purpose of the Study:

• To assess the effectiveness of random blinded rechecking as a quality assurance measure for sputum smear microscopy.
• To identify the sources and types of errors in TB diagnosis at peripheral microscopy centres and intermediate reference laboratories.
• To evaluate the performance of Senior Tuberculosis Laboratory Supervisors (STLS) in smear rechecking.

Main Methods:

• A pilot study was conducted in Delhi, involving the random blinded rechecking of 12,162 sputum slides.
• Slides were re-read by STLS at an intermediate reference laboratory after coding.
• Data analysis focused on identifying discrepant results and categorizing error types (false-positive, false-negative, quantification).

Main Results:

• A total of 204 discrepant results (1.68%) were identified out of 12,162 re-read slides.
• The majority of errors (73.5%) originated from peripheral microscopy centres, while 26.5% were attributed to STLS.
• High rates of false-negative errors (25%) and false-positive errors (8%) were observed, alongside minor errors in quantification and positivity.

Conclusions:

• The current system of random blinded rechecking requires enhanced supervision at the district level to improve efficiency and accuracy.
• Strengthening quality assurance mechanisms is essential to minimize diagnostic errors in TB detection.
• Addressing errors at both peripheral and intermediate levels is critical for reliable tuberculosis diagnosis.