But in lab, I ask students to ID tubes by color: what additive is in the green-top and the purple-top, and which test would you run from each? Extra credit if you can explain when you’d choose a 22 g needle instead of a 25 g to reduce hemolysis on a small-dog draw.
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Had a ‘tall tabby’ on a patio that was a serval; I kill the porch lights and park a sardine can near a door to keep it anchored while the permitted handler rolls, because ‘if the ears are radar dishes, it isn’t a housecat.’ If the owner can’t produce paperwork on scene, I snap a quick ear/spot pattern photo and log it, then let wildlife verify before anyone leaves. Net box beats a pole every time, but only touch it if you’re cleared to handle it.
Green-top = lithium heparin for plasma chem/electrolytes; purple-top = EDTA (K2/K3) for CBC/smear, and beware EDTA contamination falsely bumping K+ and dropping Ca. I’ll reach for a 22 g over a 25 g on a small dog with a decent vein when I can do a smooth vacuum or gentle syringe draw to reduce shear; I also “invert 8–10 times,” not shake — this isn’t a protein shake. @OP, lithium heparin tends to be the go-to in-house for electrolytes.
Quick tip: fill green before purple to prevent EDTA carryover skewing electrolytes and invert 8–10 times — “order of draw matters,” don’t shake. On tiny dogs, a 22 g can hemolyze less than a 25 g if the vein allows; draw with a syringe and use a transfer device to fill the tube — bigger straw, less foam. Do you teach syringe-to-tube transfer with a transfer device?
I always tell students: on tiny-dog draws, switch to a pediatric low‑vac holder with a 22 g butterfly instead of a 25 g straight needle — less shear, less vein collapse. For purple-tops, fill to the line and make the smear right away; , underfilled EDTA tubes wreck platelet counts, while green-tops are great for stat chem but not for smears and hemolysis will bump K/AST. @Kara here’s a quick chart I like: https://www.idexx.com/files/veterinary/reference-laboratories/sample-handling-guide.pdf — do you teach the low‑vac trick in your lab?
I’d add one thing on the purple-top: fill it to the line — underfilling concentrates EDTA and can shrink cells, faking a low HCT/MCV. For small-dog draws, you’ll see less hemolysis with a quick, straight jugular stick and transferring from a syringe via a safety transfer device instead of pushing through the needle (think “no foamy milkshakes”). @rlennox24, do you ever switch to citrate for the chronic feline platelet clumpers and back-calc?