Pathology for medical students
Within an hour after removal from the body, tissue samples should generally be placed in vessels with the correct fixing solution, with a volume that allows them to lie freely in the solution. The standard fixation fluid is generally 10% neutral buffered formalin, which is roughly equivalent to 4% formaldehyde.
The main exception to using formalin are mainly:
- A tophus or other specimen suspicious for gout versus pseudogout should be sent in alcohol or dry, since formalin will dissolve the crystals.
- Lymph nodes (or other lymphoid aggregates) with a suspicion of lymphoma, where samples are generally put in a special solution for flow cytometry.
- Products of conception with a need to take samples for genetic testing.
Orientation of skin excisions should generally be marked when there is a substantial likelihood of needing to excise further, and it is in a location where it is inconvenient to perform re-excision in all directions indiscriminately. Otherwise, skin lesions with only a mild suspicion of cancer (such as dark skin focalities in general) can usually be excised unoriented. Orientation can be made with one or two (one short and one long) sutures, designated lateral, medial etc, or o’clock positions. The direction of the margin marked by any suture should not be ambiguous (like on the border between two of them).
- When ordering vitamin D levels, generally order calcifediol (25-hydroxycholecalciferol) and/or 25-hydroxyergocalciferol, and not calcitriol (also known as 1,25-dihydroxycholecalciferol). The latter is reserved for specific endocrinology purposes.
- Don't order HbA1c in a patient who was transfused in the last 3 months, and consider a recent transfusion if a patient has a surprisingly normal HbA1c. In such patients, a fructosamine (glycosylated albumin) level is an alternative that is unaffected by transfusion, and reflects blood sugar control over the previous couple of weeks.
- . Breast pathology grossing guidelines. UCLA Health. Retrieved on 2021-09-09.
- Katarzyna Lundmark, Krynitz, Ismini Vassilaki, Lena Mölne, Annika Ternesten Bratel. Handläggning av hudprover – provtagningsanvisningar, utskärningsprinciper och snittning (Handling of skin samples - Instructions for sampling, cutting and incision. KVAST (Swedish Society of Pathology). Retrieved on 2019-09-09.
- . Paraformaldehyde, Formadehyde and Formalin. Duke University. Retrieved on 2019-12-17.
- Jennifer E. Frank, MD. Post-transfusion HbA1c. ClinicalAdvisor.