Random Blinded ReChecking [RBRC] Process

Annual slide sample and the monthly sample for Random Blinded Rechecking (RBRC) is determined by the District TB Officer (DTO), assisted by the Intermediate Reference Laboratory (IRL), Statistical Assistant (SA) or Data Entry Operator (DEO) based on Lot Quality Assurance Sampling (LQAS) method.

Under the LQAS method, sample size depends on 3 components:

1. Annual Negative Slide Volume (ANSV)
2. Slide Positivity Rate (SPR)
3. Sensitivity of picking up lower bacilli count in microscopy

Process of RBRC (Figure 1)

• The LT at each DMC stores slides for RBRC in slide boxes.
  • The laboratory must store slides in a way that allows for easy retrieval of every slide identified for the rechecking sample. Therefore, all slides are to be stored in the provided slide boxes in the same order as they are listed in the laboratory register. Slides are marked as ‘a’ and ‘b’ along with the lab serial number for first spot and early morning specimen.
  • The result of the smear examination must not be written on the slide.
  • Removal of immersion oil is to be done using tissue paper before storing slides in a slide box. Senior TB Lab Supervisors (STLS) of the district, informing them of the total number of slides to be collected every month from each DMC.
• The STLS then select the required number of slides from the Laboratory Register and the LT records the results as per Annexure B (Figure 2).

Collection of slides for RBRC explained with an example

• If the sample size is calculated to be 180 smears per year, 15 slides are to be collected during each monthly visit.
  • If the STLS observes that the laboratory processed 82 slides since the last monthly visit, they could collect for example every fifth (82/15 = 5.4 or 5th) slide randomly to obtain the required 15 slides and may begin with any number between 1 to 5, say 3.
  • The first random number may be selected by choosing last digit on any available currency note.
  • The remaining slides are chosen by adding serially 5 till 15 slides are selected.
  • In this example, the 3rd, 8th, 13th, 18th, 23rd, 28th, 33rd, 38th, 43rd, 48th, 53rd, 58th, 63rd, 68th and 73rd slides are selected to obtain 15 slides required for that month.

• Annexure B (Figure 2) is then put into an envelope and sealed. The number of slides packed is written on the top of the envelope.
• Both the slide box and the envelope are marked with the name of the respective DMC, the name of the TB Unit and district, and the month and year.
• The slide box and the sealed envelope are then taken by the STLS for handing over to the DTO.

Figure 1: Process of random blinded rechecking (RBRC) performed by (1) STLS during on-site visit to DMC and (2) at DTC (RNTCP Laboratory Network Guidelines)

Figure 2: Annexure B to document Smear Results Sheet for Blinded Rechecking (RNTCP Laboratory Network Guidelines)

The DTO is responsible for ensuring that the blinding process is strictly followed.

Resources

RNTCP Laboratory Network Guidelines.

Assessment