There are no guidelines that recommend the frequency of a screening CBC. The standard of care practiced in Ontario is generally a CBC with annual or biennial (every 2 years) bloodwork starting at age 40. In many situations, for example, a doctor may order a CBC to investigate symptoms (i.e. fatigue, hair loss, heavy bleeding in women, vegan diet to assess nutritional status etc). Most physicians will order a CBC when they are investigating a patient with symptoms, as an abnormal CBC can quickly provide necessary information to guide further testing.