Terms:
(1) carry-over
(2) floater (a piece of tissue that "floats" onto another slide in a water bath)
Sources of extraneous material on a slide:
(1) prior to receipt in the laboratory
(1a) reuse of a container, including between patients
(1b) contaminated container
(1c) dirty equipment or care area
(2) from receipt in the laboratory to staining
(2a) dirty equipment or workstation
(2b) dirty or contaminated supplies
(2c) dirty water bath
(3) from staining to covering
(3a) dirty stains
(3b) contaminated water
Rules for troubleshooting a suspected floater:
(1) If the material is present in multiple serial sections of a tissue block, then suspect something embedded in the block, rather than carry-over during staining or processing.
(2) If the material is present in only 1 section but not additional sections from the same block, then suspect carryover.
(3) If multiple different cases are affected on the same day, then consider the staining solutions or water baths as the source of contamination.
(4) If multiple different cases are affected on several days, then consider contamination in supplies, solutions or water baths. This may be hard to track down if the problem is intermittent.
(5) A step with separate handling is less likely to be contaminated that a step with batch processing.
Ways to reduce carry over:
(1) Do not reuse supplies or else be very careful in their cleaning. This may be an issue for disposable supplies that were not designed for reuse.
(2) Keep supplies used for different patients separate and well-marked.
(3) Purchase supplies of high quality from reputable sources, with additional cleaning if necessary.
(4) Keep equipment and work areas clean.
(5) Pay attention being clean and orderly whenever handling a patient sample.
(6) Inspect each lot of supplies for signs of contamination.
(7) Check water sources for debris and filter if necessary.
(8) Process slides separately if at high risk for cross-contamination.
(9) Properly filter and maintain stains and solutions used for batch processing, or else stain for single use.
(10) Keep waterbaths clean.
(11) Look at slides for signs of debris or loss of material during processing.
