Medical Laboratory Equipment, Reagents and Quality Control
What this domain tests
This domain tests equipment maintenance, calibration, reagent handling, and internal quality control. Expect questions on pipettes, centrifuges, microscopes, autoclaves, refrigerators, water quality, control materials, and Westgard rules.
Core rules
- Calibration establishes the relationship between an instrument signal and a known value; maintenance keeps equipment fit for use. Both must be documented.
- Store reagents at the stated temperature, protect them from light, and use before expiry. Bring reagents to room temperature only when the insert allows.
- Run quality control materials at the beginning of a shift and after calibration or major maintenance. Plot values on a Levey-Jennings chart.
- Common Westgard rules: 1-3s is rejection; 2-2s means two consecutive controls exceed the same 2SD limit; R-4s means the range between two controls exceeds 4SD; 4-1s and 10x indicate systematic shift.
- Autoclave monitoring uses physical, chemical, and biological indicators. Bacillus atrophaeus spores are used for dry heat; Geobacillus stearothermophilus for steam.
- Pipettes and balances need periodic verification; water for reagent preparation must meet the required grade.
Worked example
A biochemistry control shows two consecutive values above +2SD. The 2-2s rule is violated. Reject the run, do not report patient results, and investigate calibration, reagent storage, and instrument drift. The reasoning is that two values on the same side suggest systematic error, so repeating until a value looks acceptable would hide the problem.
Traps
Do not use expired or improperly stored reagents. Do not accept a run with a failed control. Do not calibrate without recording. Do not assume a normal control excludes patient sample errors. Do not autoclave liquids in sealed containers.