Sputum Smear Microscopy: Use of Quality Control Slide- QCP and QCN

One of the methods for internal monitoring of the quality of the microscopy process is the use of Quality Control (QC) slides.

QC is a systematic internal monitoring of working practices, technical procedures, equipment and materials, including quality of stains.

Quality Control Positive (QCP) and Quality Control Negative (QCN) slides are used for sputum smear microscopy quality monitoring.

Process for quality control using QCP and QCN is as follows:

• Senior Tuberculosis Laboratory Supervisor (STLS) prepares QCP & QCN slides.
• Preparation of QCP - QCP slides have to be prepared by pooling 3+ grade sputum samples.
• Preparation of QCN - QCN slides have to be prepared by pooling Negative sputum samples with an adequate number of pus cells (approximately 20 cells/field).
• While preparing each new batch of staining reagent, STLS has to use one set of QCP & QCN and its entry needs to be made in the batch register (an Internal Quality Control (IQC) document).
• STLS will supply one set of QCP & QCN to the Designated Microscopy Centre (DMC) Laboratory Technician (LT) along with each batch of reagent. The DMC LT has to stain and examine the QCP & QCN slides and enter the results in the IQC document.
• All QC slides needs to be stored for three months.

QC slides are used in the following ways​:

1. A set of one QCP and one QCN is used for monitoring the quality of a new batch of reagents prepared by the STLS​.
2. A set of one QCP and one QCN is used for a new batch of reagents prepared, by the LT at the Culture and Drug Sensitivity Testing (C&DST) laboratory​​.
3. A set of one QCP and one QCN is also supplied to DMCs along with the new batch of reagents for QC testing at microscopic centres.

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The results of QCP and QCN examination are to be documented in separate registers meant for QC.

Any discordant results require discarding the reagents prepared/ supplied.

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Resources

• Training Module (1-4) for Program Managers and Medical Officer, NTEP, MoHFW, 2020.   
• WHO: Regional Guidelines for Countries in the Western Pacific: Quality Assurance of Sputum Microscopy in DOTS Programs.  

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