Laboratory Operations, Reagents, and Instrumentation
Reagents
Operations questions test what must be documented and how instruments fail. Use analytical grade chemicals, record receipt and opening dates, store per the label (many antibodies at 2-8 °C, never frozen), and verify each new lot against the in-use lot before release. Water quality matters: CLSI reagent water types exist because high-iron or high-microbial water degrades stains, buffers and silver methods.
Instruments
- Tissue processors: daily check of fluid levels, temperature, vacuum/pressure and agitation, with run verification and a log.
- Embedding centers: paraffin 56-60 °C, cold plate functioning.
- Microtomes: blade and clearance angle set correctly, blade changed on schedule.
- Cryostats: -20 to -25 °C, daily temperature log and disinfection.
- Water baths: 40-45 °C for floating ribbons.
- pH meters: calibrated with fresh buffers each use.
Maintenance and validation
Follow preventive maintenance schedules and function checks, and document corrective action when a check fails. Verify or validate methods before patient testing and perform parallel testing for a new instrument or reagent system.
Traps
Expired reagent used because it still seems to work; an uncalibrated pH meter; an unbalanced centrifuge; wrong xylene or paraffin levels; and assuming a processor's programmed time equals its actual time, when retort heat-up adds delay.
Rule of thumb: If it is not written down, it did not happen. Every instrument has a daily check and log; every new lot has a verification record.