11/12/2025
I’ve had TWO CBCs clot on babies in over 4 years, and it’s not because I’m lucky. Proper technique and good preparation are key in avoiding any NICU nurse’s most dreaded phone call from the lab. Share your tips and tricks to avoid having CBCs clot in the comments!
1. Put a heel warmer on your patient. Depending on my patient’s perfusion, I’ll sometimes add a second heel warmer and place it on the calf, or I’ll place the foot with heel warmer inside of a diaper.
2. Use gravity to assist you by angling the head of the bed UP, with the feet lower than the chest. I’ll swaddle or restrain my patient if necessary as well, to avoid being kicked during the procedure and to comfort them, and offer a pacifier or sucrose.
3. Use an appropriately sized lancet to puncture the skin on the outer aspect of the heel. You should never have to upsize your lancet to keep a specimen from clotting.
4. Work with gravity and the flow of blood, not against it. A common mistake that I see is that people will raise the head of the bed, but then they also inadvertently pull the patient’s leg up in the air, too.
5. Avoid scraping the specimen tube against the patient’s skin to avoid having skin cells mix in with my sample, which can cause clotting. Let big drops of blood fall into the tube without squeezing the lower extremity. The more scraping that you do, the more likely that you are to have your specimen clot. If bloodflow is slowing, pump the leg back and forth or briefly massage the calf.
6. The purple top tube that we use to collect CBCs has an additive called EDTA. EDTA is an anticoagulant, and it works by binding to calcium ions in the blood. EDTA inhibits the coagulation cascade, but it doesn’t affect cell counts. Overfilling and overshaking your tube actually increases the chances of hemolysis or clotting. Instead, gently invert your tube 8 to 10 times, end over end, to ensure that the EDTA mixes to prevent clotting.
