What is a CBC blood test?
Last updated September 3, 2026.
A CBC - complete blood count - measures your red blood cells, white blood cells, and platelets: the workhorse panel of medicine. Low red cells signal anemia, white-cell shifts point toward infection or immune problems, and platelets reflect clotting. It screens at physicals and investigates fatigue, fever, bruising, or weakness, with no fasting needed. One slightly out-of-range number is a conversation, not a crisis.
What to do
- Expect it often. Physicals, fatigue workups, and infection checks all run a CBC - it is routine, not alarming.
- No fasting needed. Eat and drink normally unless another test on the same order says otherwise.
- Read the pattern, not one number. Your doctor interprets the counts together against your symptoms.
- Ask about the differential. The white-cell breakdown often explains what the total count cannot.
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