Complete blood count (CBC): how to read each value

The complete blood count (CBC) is probably the most frequently ordered blood test of all. It shows up in almost every check-up and consultation. But when you look at a report full of abbreviations — Hb, Hct, WBC, platelets, MCV — it is easy to get lost. This guide helps you understand what it measures and how to read each part without being a doctor.

What is a complete blood count?

The complete blood count counts and characterizes the cells circulating in your blood. Those cells fall into three lines:

• Red cell line: the red blood cells, which carry oxygen. This is where hemoglobin and hematocrit belong.
• White cell line: the white blood cells (leukocytes), the body's defense against infection.
• Platelets: the cell fragments involved in clotting.

That is why a single test gives so much information: these three lines can point toward conditions as different as anemia, an infection or a clotting problem.¹

Reference ranges (a guide)

These are the reference ranges that Laboratorio Aclimu reports for adults (CELL-DYN method, EDTA whole blood). Ranges vary by laboratory, sex and age; always compare against the reference range printed on your own report.

Value	Reference range (Aclimu)	What it assesses
Hemoglobin (Hb)	11.7–17.4 g/dL (male) · 11.5–16.1 g/dL (female)	Oxygen transport · anemia
Hematocrit (Hct)	35–50% (male) · 34–47% (female)	Proportion of red cells
Leukocytes (WBC)	3,800–10,600 /mm³ (male) · 3,600–11,000 /mm³ (female)	Defense · infection and inflammation
MCV	80–100 fL	Size of the red cells

The red cell line: hemoglobin, hematocrit and anemia

Hemoglobin is the protein that carries oxygen; hematocrit is the percentage of blood volume taken up by red cells. When they are low, we talk about anemia. The complete blood count also includes the "indices" (such as the MCV, the volume of each red cell) that help point toward the type of anemia: small red cells, for example, often suggest iron deficiency. To confirm that cause, an iron study (ferritin) is usually added.¹

The white cell line and platelets

White blood cells rise mainly with infection and inflammation (leukocytosis) and can fall because of viruses or some medications (leukopenia). The complete blood count also breaks down the types of leukocytes (neutrophils, lymphocytes and so on), which helps suggest whether an infection is more bacterial or viral. Platelets, in turn, matter for clotting: both low and very high values deserve evaluation.¹

What should you do if a value is out of range?

A slightly abnormal value does not always mean disease: it may be due to something temporary. The key is not to read each number in isolation, but together and alongside your symptoms. Your doctor is the one who interprets the whole pattern and decides whether a test needs to be repeated, expanded or investigated further. The complete blood count is an excellent tool for orientation, not a diagnosis on its own.

At Laboratorio Aclimu

At Laboratorio Aclimu (Marcelo T. de Alvear 2337, Recoleta (Barrio Norte), Buenos Aires) the complete blood count is part of every routine check-up and of our general clinical tests, in a single blood draw alongside blood glucose, kidney and liver function, a lipid panel, uric acid and a complete urinalysis. You can book online, with or without a doctor's order if you come as a private patient.

This article was reviewed by the biochemistry team at Laboratorio Aclimu. The information is for general guidance and does not replace a consultation with your doctor or health professional.

Frequently asked questions

What does a complete blood count measure?

A complete blood count measures the three cell lines in your blood: red cells (with hemoglobin and hematocrit), white cells (leukocytes) and platelets. It is one of the most widely used tests because it gives a general picture of your blood and can point toward anemia, infection, inflammation and other conditions.

What does low hemoglobin mean?

Hemoglobin below the normal range indicates anemia: your blood carries less oxygen. The most common cause is iron deficiency, though there are others. Anemia can cause tiredness, paleness and shortness of breath on exertion. To find the cause, an iron study (ferritin) is usually added.

What do high or low white blood cells mean?

White blood cells (leukocytes) are the body's defense. They rise (leukocytosis) mainly with infection and inflammation, and can fall (leukopenia) because of viruses, some medications or other causes. The value is always interpreted together with your symptoms and the rest of the complete blood count.

Do I need to fast for a complete blood count?

At Laboratorio Aclimu the complete blood count is done after a minimum 8-hour fast (you may drink water). If you take any medication, let the staff know; in general you do not need to stop it unless your doctor says otherwise. We confirm the instructions when you book.

References

1. Tefferi A, Hanson CA, Inwards DJ. How to interpret and pursue an abnormal complete blood cell count in adults. Mayo Clin Proc. 2005;80(7):923-936. Available at: pubmed.ncbi.nlm.nih.gov
2. MedlinePlus, U.S. National Library of Medicine (NIH). Blood count (complete blood count). Available at: medlineplus.gov
3. World Health Organization. Anaemia. Available at: who.int