After fits or vomiting, neutrophil and other white blood cell counts can increase falsely. But if the reason for seizures or vomiting is an infection, it improves the white blood cell counts.
But white blood cell count can increase, followed by fits or vomiting without any infection or inflammation.
Normal blood flow in vessels is laminar flow. That means blood flows as circular-shaped layers with velocity gradients. The central blood column has the highest speed. Most peripheral blood layer has very slow velocity. Because of that, white blood cells in the peripheral column of blood can attach to the vessel wall easily.
But after fits or vomiting, these white blood cells detach from the vessel wall and enter the middle blood column. If the blood samples are taken for the investigations just after the vomiting or seizure episode, the sample can contain white blood cell concentration. This can lead to a false elevation of the white blood cell count.