What your complete blood count (CBC) can reveal about your health

A Complete Blood Count (CBC) is one of the most common blood tests doctors order—and for good reason. This single test offers a window into your overall health by measuring the major components of your blood: red blood cells, white blood cells, and platelets. Each of these plays a critical role in how your body functions, and changes in their levels can signal a wide range of conditions.

What the CBC Measures

A CBC includes many values, but the most important ones for most people are:

• Hemoglobin (Hgb):A protein in red blood cells that carries oxygen. Low hemoglobin often means anemia, which can cause fatigue, shortness of breath, and dizziness.

• Hematocrit (Hct):The percentage of blood made up of red blood cells. It usually drops when someone is anemic or dehydrated.

• White Blood Cell Count (WBC):These cells are the defenders of your immune system. High counts can mean infection or inflammation; low counts may occur with viral infections or certain medications.

• Platelets (Plt):Platelets help your blood clot. A low platelet count increases bleeding risk, while a high count can be a sign of inflammation, iron deficiency, or other conditions.

What Abnormal Results May Mean

• Low hemoglobin or hematocrit:Most commonly caused by iron deficiency, blood loss, or chronic conditions such as kidney disease.

• High white blood cell count:Often indicates infection, stress, inflammation, or—less commonly—a bone marrow disorder.

• Low white blood cell count:May occur due to viral illness, autoimmune disease, or medication effects (like chemotherapy).

• Abnormal platelets:Low platelets can be caused by viral infections or immune-related disorders; high levels may indicate inflammation or a bone marrow condition.

When to Talk to Your Doctor

An abnormal CBC doesn’t always mean something serious. Many small fluctuations are temporary. But you should speak with your clinician if your results are far outside the normal range or you’re experiencing symptoms such as fatigue, bruising, unusual bleeding, fever, or persistent infections.