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Anonymous asked: hematology histograms (how to read them/compare with a peripheral blood smear), por favor?
Sure thing! A lot of people just glance at them since the numbers are what really drive the testing process (when to do a manual differential, when to look at the history, etc), but the histograms are pretty helpful in anticipating what to expect in a smear.
Anon left asks about this in rapid succession, so I guess that is my cue to talk about megaloblastic anemia, haha.
Megaloblastic anemia is a non-hemolytic anemia, usually attributed to either B12 deficiency (impaired absorption because of a gastrectomy, pernicious anemia, inflammation, or transcobalamin deficiency) or Folate deficiency (dietary, drug related impairment of use, loss though kidney). Both are cofactors in DNA synthesis, especially of thymidine. The result is nuclear cytoplasmic asynchrony wherein the nucleus matures slower than the cytoplasm, and you can see all the cells are a little off looking as a result.
In your smear, you won’t see much in the way of retics, but there will be extensive hypersegmentation of neutrophils, large platelets, huge macrocytes/macroovalocytes, tear cells, schistocytes, pancytopenia, and howell-jolly bodies. A few giant bands and metamyelocytes much sneak into the circulation too. Things are generally just. Big.
The bone marrow will have very distinct megaloblastic changees. The myeloid:erythroid ratio will be decreased but the marrow is almost always hypercellular. Very early erythroid precursors predominate over late precursors because of ineffective erythropoiesis. In contrast to the comically large myeloid precursors, megakaryocytes are small and hypolobated because they have so much DNA they are affected the most by impaired synthesis.
Allergy testing wasn’t something I learned in school, likely because the tests that exist right now are admittedly not very good. So when I ended up on the Allergy Bench I was a little bit boggled that there was a whole bench for it. Hopefully this will be an acceptable crash course in it.
The Kleihauer Betke Test:
A peripheral blood smear of the mom’s blood is prepared and fixed in 80% ethanol. It is then treated with acid (McIlvaine’s buffer) and stained with eosin and hematoxylin. Fetal cells will remain in tact and stain bright pink because of the high HbF/fetal hemoglobin content which resists acid elution. Adult hemoglobin in maternal cells will elute out, leaving faintly staining “ghost cells”. The percental of fetal cells per 2000 cells is used to determine how much extra WinRho (in 300mg vials) is required:
Vials = %fetal cells x maternal blood volume (~5000mL)/30mL
Rounded to the nearest whole number + 1 extra. But that one extra is usually the shot they automatically gave her after she gave birth.
The Rosette Test / Screen for fetal-maternal bleeds
After the baby is born, we take their cord blood (which is thick and gross, by the way) and do a forward ABORh on them. If they are D positive or weak D positive and the mother is negative, the hospital will do an onsite rosette test:
A 3% cell suspension of the mother’s blood is incubated with chemically modified anti-D which will bind to any infant cells. Unbound antibody is washed away and indicator cells (O positive cells treated with ficin to increase reactivity) will bind with infant cells to make little microscopic rosettes/clumps which you can look for with an inverted mic:
All eligible mothers will receive another shot of WinRho regardless of the result because the clumps can be hard to see. However, positive screens indicate a fetal bleed over 30mL (which occurs in about 0.3% of pregnancies), in which case, the mother might need a larger dose, determined by a Kleihauer-Betke (in tomorrow’s post). The WinRho is administered within 72hours because once mom’s discharged, it’s really hard to hunt a lady who just gave birth down just to give her another needle!
So what’s the deal with HDFN?
This is sort of a intro to the disease and a less slapdash intro to pre-natal testing. I personally am not very excited by the prenatal part of it, but it’s important. I tried to do this assuming very limited knowledge of blood banking, but it is kind of an esoteric discipline so please ask if something I wrote has completely boggled you.
Well, it’s been a while, but let’s talk about lab tests again. I’ve chosen Ketones this time because they’re so simple.
Chlamydospores in Candida albicans, wet mount.
The Dalmau test was used to help ID C. albicans once upon a time but phased out before I got into the labs. It was essentially growing a yeast in unfavourable environments to see if they formed chlamydospores in response to the stress. Cornmeal agar (minimal nutrient qualities) was used and the inoculum would be covered with a coverslip to decrease the amount of oxygen available to the growing yeast.