Mindray BS3600: recurring WBC count error with normal controls
What happened
As reported in the case, every second sample triggered a count/aperture error on the WBC channel while control values stayed within range; bleach rinsing of the probe and hydraulic path did not clear it.
What was checked
- Rinsed the sampling probe and soaked the hydraulic system with bleach; the error kept returning.
- Inspected the aperture under a microscope; nothing conclusive was found.
- Confirmed fluid movement along the WBC channel tubing and the valve upstream of the aperture, pulling bleach from the counting chamber through the aperture with a syringe.
- Checked the sensors on the volumetric tube: per the case, the error is raised when the second sensor does not trigger within roughly 25 seconds.
- Worked through the valves one by one; suspicion fell on the lyse reagent valve because foam was seen passing through it.
Cause
In this case the probable cause was foam passing through the lyse reagent valve: bubbles travelled into the WBC counting chamber and the volumetric tube and disrupted the count, which explains why the error hit samples while the controls ran clean.
The cause is probable and was not fully confirmed.
What was done
The problem with the lyse reagent valve was eliminated (valve replaced or restored), after which the error reportedly stopped repeating; the engineers stressed that the root cause remains probable rather than fully confirmed.
Safety
Treat every sample and reagent spill as potentially infectious, wear gloves and eye protection when handling bleach and lyse reagent, and run quality control before returning the analyzer to routine use.
Lesson: When count errors repeat on samples but QC stays normal, look beyond the aperture to foam sources upstream, because a foaming or leaking reagent valve can feed bubbles straight into the counting path.
Covered in the course: Lab Analyser Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.