AMCA MHTC common mistakes
AMCA MHTC · Understand the traps and how to avoid them.
Calculating fixative volume by estimating tissue size instead of weighing the specimen, so specimens are immersed in less than the 10:1 formalin-to-tissue ratio.
Candidates eyeball a biopsy or a slice and assume a 'standard' container of formalin is enough, forgetting that the ratio is by mass and that hollow or fatty tissue needs extra volume.
What to do instead
Weigh the specimen on a balance, record the mass, and calculate the minimum formalin volume as 10 times that mass; then confirm the container actually holds that volume after the tissue is added.
Cutting cassettes thicker than about 3-4 mm or leaving two similar-sized pieces in one cassette, producing under-fixed or under-processed centres.
Candidates try to save cassettes or preserve the whole specimen, not realising fixative and processing fluids penetrate only a few millimetres per hour and that thick blocks section poorly.
What to do instead
Trim to no more than 3-4 mm thick, keep one piece per cassette unless pieces are very small, and orient flat surfaces so the cut face is exposed to fluid.
Setting the microtome clearance angle to zero or leaving it at the factory default regardless of blade type, causing chatter, vibration, or a compressed section.
Candidates confuse clearance angle with rake angle or assume any blade works at any angle, and they do not inspect the section for chatter under the microscope.
What to do instead
Set clearance angle per blade geometry (typically around 5 degrees for a wedge/steel knife and per the blade manufacturer's spec for disposable low-profile blades), then check for uniform thickness and absence of venetian-blind chatter.
Reporting a special stain as positive without running a positive control or verifying that the expected internal control elements stained correctly.
Candidates focus on the lesional area and treat a coloured result as a valid result, forgetting that a failed stain can mimic a negative or a false positive.
What to do instead
For every special stain batch, include a known positive control slide and evaluate internal controls (e.g., organisms or tissue elements expected to stain); if controls fail, repeat the stain before interpreting.
Handling formalin and xylene without confirming the correct glove material and without using a fume hood for open manipulations.
Candidates assume 'gloves are gloves' and that a benchtop is fine if the room smells acceptable, ignoring that latex offers poor protection against xylene and that odour threshold is not a safety threshold.
What to do instead
Use nitrile gloves for formalin and xylene tasks, change them when contaminated, and perform all open-container work in a ventilated hood or with local exhaust; know the SDS for each reagent before use.
Accepting a run when the daily QC slide (e.g., a known control section stained with H&E) shows poor colour balance, rather than investigating before releasing slides.
Candidates treat QC as a paperwork step and release slides because the batch 'looked okay' or because the clinician is waiting.
What to do instead
Evaluate the control slide against defined acceptance criteria (nuclear detail, eosinophilia, no precipitate) before releasing any slide; document the result and hold or repeat the batch if criteria fail.
Failing to verify that the processor's reagent stations were changed on schedule and that wax is free of clearing agent carryover.
Candidates trust the instrument's programmed cycle and do not check the reagent log or inspect wax clarity, so contaminated reagents silently degrade processing.
What to do instead
Check and initial the reagent-change log against the schedule, inspect wax for cloudiness or solvent smell, and confirm the processor completed its cycle and reached the correct vacuum/pressure and temperature setpoints before loading.
Placing a specimen in formalin after it has dried out or after a delay, without documenting the delay and ischaemia time.
Candidates assume formalin 'fixes everything' and do not record warm ischaemia or time-to-fixation, which affects downstream antigen and morphology quality.
What to do instead
Record time of excision, time placed in fixative, and fixative type on the request form; if delay occurred, note it so the pathologist can interpret staining and antigen results appropriately.
Floating a ribbon on a water bath that is too hot or too cold and mounting sections with folds or bubbles.
Candidates do not check bath temperature and rush the transfer, so sections over-expand, wrinkle, or trap air under the section.
What to do instead
Set the bath a few degrees below the wax melting point, verify with a thermometer, float the ribbon until wrinkles just relax, and lift the slide smoothly from below the section to avoid bubbles.
Discarding or overwriting troubleshooting evidence (blocks, slides, reagent lot numbers) before the cause of a problem is identified.
Candidates clean up quickly or release the case, losing the ability to trace a staining or sectioning failure to its source.
What to do instead
Retain representative blocks, slides, and reagent lot records until the investigation is closed; document the lot numbers, instrument logs, and corrective action taken.