A CBC describes blood cells. Hemoglobin measures the oxygen-carrying protein in red cells, while hematocrit describes the red-cell share of blood volume. Read them together with symptoms, previous reports, units and the laboratory’s reference ranges.
What can a CBC tell you?
A complete blood count provides information about red cells, white cells and platelets. It supports health assessment and monitoring of conditions involving blood cells. Looking at the pattern helps make a follow-up discussion more useful. MedlinePlus explains the components of a CBC.
On small screens, swipe the table horizontally to read every column.
| Test | What it tells you | Read alongside |
|---|---|---|
| RBC | The number of red blood cells. | Hemoglobin, hematocrit and cell size. |
| Hemoglobin (Hb) | The protein that transports oxygen in red cells. | Units, earlier results and symptoms. |
| Hematocrit (Hct) | The fraction of blood volume occupied by red cells. | Hydration and other CBC results. |
| MCV | Average red-cell size. | The pattern alongside Hb and other measurements. |
| WBC / Platelets | White-cell count / platelet count. | Recent illness, medicines and clinical assessment. |
How are hemoglobin and hematocrit different?
Both concern red cells, but they measure different things and use different units. For example, an Hct of 44% describes a 44% red-cell share of sample volume. This illustrates the unit; it is not a universal target. Understanding hematocrit.
Why does context matter?
Dehydration, smoking, altitude and health conditions can influence Hb or Hct. Low Hb also has several possible explanations. Symptoms, medicines and activity history help interpret the result before deciding on care. Factors affecting hemoglobin.
Prepare for a useful follow-up
- Keep the complete report, date, units and reference ranges.
- Place old and new reports together and mark your questions.
- Record fatigue, dizziness, recent illness or blood loss.
- Bring your medicine and supplement list and relevant history.
A CBC usually needs no special preparation. Other tests ordered with it may require fasting, so follow the laboratory’s instructions. Preparing for a CBC. Ask, “What does this pattern suggest, and which result needs follow-up?” Use the reference range on the report. Reading laboratory results.
Frequently asked questions
Are CBC and hematocrit the same test?
A CBC is a group of measurements. Hematocrit is one measurement describing the red-cell share of blood volume.
Does low hemoglobin always mean iron deficiency?
No. Low Hb has several possible causes. Other results and clinical history help determine appropriate care.
Do I need to fast for a CBC?
A CBC usually needs no special preparation. Follow laboratory instructions when other tests are ordered with it.