Your CBC is the most common blood test on Earth — and the most ignored. Three numbers do most of the talking. Here's how to read yours in the time it takes to finish a coffee.
Hemoglobin — your oxygen score
Hemoglobin (Hgb) is the protein inside red cells that ferries oxygen from your lungs to everywhere else. It's the single most useful number on the page.
Low hemoglobin = anemia. It can make you tired, breathless, pale, or cold in the hands and feet. The #1 cause worldwide is iron deficiency — but B12 deficiency, blood loss, and long-term illness count too.
High hemoglobin is far less common and often just means dehydration, high-altitude living, or smoking. Re-hydrate and re-test before worrying.
White cells — your defence force
The total white-cell count (often labelled TLC) is your immune system's headcount. Normal sits around 4–11 (×10⁹/L).
- Fighting an infection or inflammation
- Recent stress or hard exercise
- Certain medicines (e.g. steroids)
- A recent viral illness
- A reaction to medication
- Rarely, a bone-marrow problem
Platelets — your repair crew
Platelets are tiny fragments that plug leaks and clot blood. Typical range: 150–410 (×10⁹/L).
Very low platelets with new bruising, gum bleeding, or tiny red skin spots needs same-day medical attention — this is the classic warning sign in dengue. Don't wait it out.
The red-cell detectives: MCV, MCH, RDW
Two people can have the same low hemoglobin for completely different reasons. These indices are how your doctor tells them apart — you don't need to memorise them.
- MCV — average cell size
Small cells point to iron deficiency or thalassemia trait. Large cells point to B12 or folate deficiency.
- MCH / MCHC — hemoglobin per cell
How much oxygen-carrying protein each cell holds. These usually move with MCV.
- RDW — how uneven the cells are
A high RDW is often the earliest sign of iron deficiency, showing up before hemoglobin even drops.
Don't panic over one number
"My report has a value outside the range, so something is wrong with me."
Lab ranges are set so a small slice of perfectly healthy people fall outside them by design. Context and trend matter far more than one flag.
When to actually call your doctor
Book a visit promptly — don't wait — if you see any of these:
- Hemoglobin well below range, especially with fatigue or breathlessness
- A very low platelet count with new bruising, gum bleeding, or red skin spots
- A white-cell count that is markedly high or low
- Any value the lab has flagged "critical"
Do I need to fast before a CBC?
No. A CBC doesn't require fasting — though if it's bundled with sugar or lipid tests, those might.
My value is 0.1 outside the range. Should I worry?
Almost never. That's well within normal day-to-day and lab-to-lab variation. Your doctor looks at the whole picture and the trend.
How often should I repeat it?
Only as your doctor advises. For a flagged value, a simple repeat test in a few weeks is often the most useful next step.
A CBC explains the numbers — it doesn't replace a conversation with your doctor, who can repeat the test and place it in context.
This article is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition.