Measures for Quality Assurance in Microscopy

Sputum smear microscopy is an integral part of the National TB Elimination Programme's (NTEP’s) diagnostic services and can majorly impact the success of the programme.

It is essential to have a credible and well-established quality assurance system to assess the performance of the microscopy service.

NTEP has implemented a multi-level quality assurance network system of sputum smear microscopy in the country consisting of: 

1. Internal Quality Control (IQC)
2. External Quality Assessment (EQA)
3. Quality Improvement (QI)

• Internal Quality Control is a process of effective and systematic internal monitoring of the working practices.
  
  • It includes technical procedures, checking instruments, quality of new batches of staining solution, smear preparation, grading, equipment infection control measures, waste management, etc.
  • For the purpose of IQC, it should be ensured that all staining reagents’ dye content is mentioned on the bottle, concentrated acids are stored carefully in separate containers and stains are filtered before use.
  • Further, after each new batch of reagents is made, Quality Control Positive (QCP) and Quality Control Negative (QCN) slides should be prepared by the Senior TB Lab Supervisor (STLS) for quality control.
  • QCP slides should be prepared by pooling 3+ grade sputum samples, while QCN slides are to be prepared by pooling negative sputum samples with an adequate number of pus cells (≥10 pus cells/ field).
  • One set of QCP-QCN slides should be stained by STLS and another set should be given to the Designated Microscopic Centre (DMC) Lab Technician (LT) along with the reagent, and the results of both should be entered in the batch register/ IQC document.
  • All quality control slides should be stored for a maximum period of Four months. For the microscope, the lens should be cleaned with tissue paper after examining each slide and stored inside a microscope box at the end of the day.
  • The microscope box should contain silica gel and an electric bulb of 10-15 watts for desiccation to prevent fungal growth on the lens. The silica gel should be dehydrated periodically under direct sunlight. All microscopes should be covered under the Annual Maintenance Contract (AMC) with routine preventive maintenance.

• External Quality Assessment (EQA) is a process to assess the performance of the peripheral laboratories by a more competent laboratory, like the intermediate or the national reference laboratory. 
  
  • EQA has 3 components:

1) Onsite evaluation of peripheral laboratories by the supervisors from the reference laboratory under actual working conditions, in order to review the internal quality control mechanisms in place.

2) Panel testing of the slides (unstained and stained) received from the reference laboratory by all the STLS and the peripheral laboratory LT to evaluate the smear microscopy process. This helps to determine whether the LT can adequately perform Acid-fast Bacilli (AFB) smear microscopy.

3) Random blinded re-checking of a small sample of routine slides (both positive and negative) in the peripheral laboratory by the reference laboratory to assess the accuracy of the reading.

• Quality Improvement (QI) is a process by which all components of smear microscopy diagnostic services are continuously monitored and carefully analysed with the aim to identify the problems and implement corrective actions (including retraining) to prevent the recurrence of the problems.