Question 1 · Hard
A liver biopsy and a reticulin control are stained by the Gordon and Sweets method: acidified potassium permanganate, oxalic acid, iron alum, ammoniacal silver, formalin reduction, gold chloride toning, sodium thiosulfate and a nuclear fast red counterstain. At sign-out both slides look correct, with sharp black fibers on a clean, pale background. Ten days later, when the slides are taken from the file for a teaching session, the background of both has turned gray-brown and the fibers are hard to pick out. A trainee ran this batch; slides stained the same day by an experienced colleague with the same reagents are still clean. The most likely cause is:
- AFormalin reduction step stopped too early
- BSodium thiosulfate step omitted after toning
- COxalic acid bleach skipped after permanganate
- DGold chloride toning left out of the run
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Answer: B · Sodium thiosulfate step omitted after toning
Sodium thiosulfate (hypo) forms soluble complexes with silver that was not reduced to metal and removes it from the section before mounting. If the step is skipped, the slide looks correct at first, but the leftover silver salts are light-sensitive and slowly reduce to dark metallic silver, so the background grays over the following days. Missing gold toning, a skipped oxalic acid bleach or short formalin reduction would show at once, as brown fibers, a brown permanganate residue or weak fibers, before the slides were ever filed. The colleague's clean slides with the same reagents point to a step missed in the trainee's run. Spare sections should be restained with every step done, and the trainee's competency on the method reviewed.
- A: Short formalin reduction gives weak fibers at once, not a background that darkens later.
- C: Leftover permanganate would leave a brown background at once, not after days.
- D: Without gold toning the fibers would look brown rather than black from the start.