Band cells (also sometimes called "stabs" in some places) are immature neutrophils.
They can appear in large numbers when patients have a chronic infection or inflammatory process. (example: When the body is trying to crank out as many neutrophils as possible to continue fighting a chronic bacterial infection). I'd give you a more specific Differential list but it would range all the way from Acute appendicitis to Myelodysplastic syndrome all the way down to steroid-resistant WeberChristian disease.
Segmented Neutrophils (Segs) are the mature neutrophils...all decked out and ready to get their phagocytosis on.
So if you have a White blood cell count, a segs percentage and a bands percentage...you can use a simple formula to calculate the "Absolute Neutrophil Count (ANC)" which is useful for a variety of things such as monitoring the administration of colony stimulating factor or assessing a patient's risk of infection during administration of chemotherapy.
Ok back to work I go
Good luck to ya on your rotation.
-Richie
And we'll find you a picture here too....TADA!