CBC

Your doctor is likely to order a CBC if you're experiencing any of the following, or simply as part of a routine annual health checkup:

• Persistent fatigue, weakness, or unusual paleness
• Unexplained fever, chills, or frequent infections
• Unusual or easy bruising and bleeding
• Shortness of breath or a racing heartbeat
• Before a scheduled surgery or major medical procedure
• As part of monitoring a known chronic condition or ongoing medication

Because a CBC is so broadly informative, many doctors include it as a baseline test even when symptoms are mild or non-specific, since subtle abnormalities can point toward a problem well before it becomes serious.

A single CBC can surface clues toward a wide range of conditions, which is part of why it remains such a cornerstone test:

• Iron-deficiency and other forms of anemia
• Bacterial or viral infections (typically shown by a raised white cell count)
• Blood cancers such as leukemia or lymphoma
• Clotting and bleeding disorders linked to low platelet counts
• Bone marrow disorders that affect cell production
• Dehydration, reflected in an elevated hematocrit

A CBC rarely gives a final diagnosis on its own — an abnormal result is usually the starting point for further, more targeted testing.

1. No fasting is required for a standard CBC, so you can eat and drink normally beforehand unless it's being drawn alongside another test that does require fasting.
2. Wear a short-sleeved or loose-sleeved top to make it easy for the phlebotomist to access a vein in your arm.
3. Mention any medications, supplements, or recent illnesses to the lab staff, since some of these can subtly influence cell counts.
4. Stay well hydrated before your appointment, as this makes the blood draw itself easier and more comfortable.

Reference ranges differ slightly by lab, method, and by the patient's age and sex — always read your CBC report alongside the lab's own reference column rather than relying purely on general figures.

Values below the normal range for hemoglobin and hematocrit typically point toward anemia, while a raised white cell count often signals infection or inflammation, and a low platelet count can indicate an increased bleeding risk — your doctor will interpret the full picture together rather than any single number in isolation.