Final answer:
Blood cell counters cannot detect certain abnormalities, so a differential blood film is needed.
Step-by-step explanation:
The abnormalities mentioned in the question will not be evident with blood cell counters and must therefore be detected using the differential blood film. Blood cell counters are automated machines that analyze blood samples for various parameters, such as red blood cell count, white blood cell count, and platelet count. However, they may not be able to detect certain abnormalities or subtle changes in blood cells that can be observed under a microscope on a differential blood film.