The complete blood count — or CBC — is the single most commonly ordered blood test in medicine. Every emergency room visit, annual physical, and pre-surgical workup includes one.
Yet most people get their results back and have no idea what the numbers mean. RBC, WBC, MCV, MCH, MCHC, RDW, MPV — it reads like alphabet soup. This guide translates every line on your CBC into plain language.
What a CBC measures
A CBC evaluates three populations of cells that circulate in your blood:
| Cell type | What it does | Key measurements |
|---|---|---|
| Red blood cells (RBC) | Carry oxygen from lungs to tissues | RBC count, hemoglobin, hematocrit, MCV, MCH, MCHC, RDW |
| White blood cells (WBC) | Fight infections and disease | WBC count, neutrophils, lymphocytes, monocytes, eosinophils, basophils |
| Platelets | Form clots to stop bleeding | Platelet count, MPV |
A "CBC with differential" — the most common version ordered — includes the white blood cell breakdown into subtypes.
Red blood cell values
RBC count
The number of red blood cells per microliter of blood.
| Reference range | Men | Women |
|---|---|---|
| Normal | 4.5–5.5 million/µL | 4.0–5.0 million/µL |
High RBC (polycythemia): can indicate dehydration, chronic hypoxia (lung disease, sleep apnea, high altitude), smoking, or rarely polycythemia vera (a bone marrow disorder). Low RBC (anemia): can indicate iron deficiency, B12/folate deficiency, chronic disease, blood loss, or bone marrow problems.
Hemoglobin (Hgb)
The protein inside red blood cells that actually carries oxygen. This is often the single most important number for assessing anemia.
| Reference range | Men | Women |
|---|---|---|
| Normal | 13.5–17.5 g/dL | 12.0–16.0 g/dL |
Low hemoglobin is the definition of anemia. Below 10 g/dL is moderate anemia; below 7 g/dL is severe and may require transfusion. High hemoglobin mirrors high RBC causes — dehydration, chronic hypoxia, or polycythemia vera.
Hematocrit (Hct)
The percentage of your blood volume occupied by red blood cells.
| Reference range | Men | Women |
|---|---|---|
| Normal | 38.3–48.6% | 35.5–44.9% |
Hematocrit moves in parallel with hemoglobin. It is particularly affected by hydration status — dehydration concentrates the blood and raises hematocrit artificially.
MCV (Mean Corpuscular Volume)
The average size of your red blood cells, measured in femtoliters (fL). This is the key to classifying the type of anemia.
| MCV value | Classification | Common causes |
|---|---|---|
| Below 80 fL | Microcytic (small cells) | Iron deficiency, thalassemia, chronic disease |
| 80–100 fL | Normocytic (normal size) | Chronic disease, acute blood loss, kidney disease |
| Above 100 fL | Macrocytic (large cells) | B12 deficiency, folate deficiency, alcohol, liver disease, hypothyroidism |
MCV is one of the most diagnostically useful numbers on the entire CBC. If your hemoglobin is low, MCV tells your doctor where to look next.
MCH and MCHC
MCH (Mean Corpuscular Hemoglobin): the average amount of hemoglobin per red blood cell. Normal: 27–33 picograms (pg).
MCHC (Mean Corpuscular Hemoglobin Concentration): the average concentration of hemoglobin within red blood cells. Normal: 32–36 g/dL.
These correlate with MCV and help confirm the type of anemia. Low MCH/MCHC with low MCV points to iron deficiency. High MCH with high MCV points to B12 or folate deficiency.
RDW (Red Cell Distribution Width)
Measures the variation in red blood cell size. Normal: 11.5–14.5%.
A high RDW means your red blood cells vary a lot in size — some are big, some are small. This is often the earliest sign of a developing nutritional deficiency (iron, B12, or folate) before other values change. RDW has also been identified as an independent predictor of all-cause mortality in multiple studies — making it an underappreciated longevity marker.
White blood cell values
Total WBC count
The total number of white blood cells per microliter. Normal: 4,000–11,000/µL.
High WBC (leukocytosis): most commonly caused by infection, inflammation, stress, or medication (corticosteroids). Extreme elevations (above 30,000) warrant urgent evaluation.
Low WBC (leukopenia): can indicate viral infection, autoimmune conditions, bone marrow problems, or medication effects (chemotherapy, some antibiotics).
The differential: five white blood cell subtypes
This is where the real diagnostic information lives.
| Cell type | Normal % | Normal absolute | What it does |
|---|---|---|---|
| Neutrophils | 40–70% | 1,800–7,700/µL | First responders to bacterial infection |
| Lymphocytes | 20–40% | 1,000–4,800/µL | Adaptive immunity (T cells, B cells, NK cells) |
| Monocytes | 2–8% | 200–800/µL | Clean-up crew; become macrophages in tissue |
| Eosinophils | 1–4% | 100–500/µL | Fight parasites; involved in allergies and asthma |
| Basophils | 0–1% | 0–200/µL | Involved in allergic and inflammatory responses |
Key patterns:
- High neutrophils (neutrophilia): bacterial infection, acute stress, corticosteroid use, smoking
- High lymphocytes (lymphocytosis): viral infection (mono, COVID, flu), chronic lymphocytic leukemia
- High eosinophils (eosinophilia): allergies, asthma, parasitic infection, drug reactions
- High monocytes (monocytosis): chronic infection, autoimmune disease, recovery from acute illness
- Low neutrophils (neutropenia): can be medication-induced, viral, autoimmune, or ethnic (benign ethnic neutropenia is common in people of African descent)
NLR (Neutrophil-to-Lymphocyte Ratio)
Not always printed on the report, but easily calculated: divide absolute neutrophils by absolute lymphocytes. Normal: 1–3. An NLR above 3 suggests systemic inflammation. Above 6 is associated with poor outcomes in cardiovascular disease, cancer, and critical illness. This ratio is increasingly used in research as a simple, cheap marker of chronic inflammation.
Platelet values
Platelet count
Normal: 150,000–400,000/µL.
High platelets (thrombocytosis): often reactive — caused by infection, inflammation, iron deficiency, or post-surgery. Rarely, a myeloproliferative disorder.
Low platelets (thrombocytopenia): can indicate immune destruction (ITP), viral infection (dengue, HIV, hepatitis C), medication effects, liver disease with portal hypertension, or bone marrow issues. Below 50,000 increases bleeding risk; below 10,000 is a medical emergency.
MPV (Mean Platelet Volume)
The average size of your platelets. Normal: 7.5–12.0 fL.
Young, newly produced platelets are larger and more active. A high MPV with low platelet count can indicate that the body is producing platelets rapidly to compensate for destruction. MPV has also been studied as a cardiovascular risk marker — higher MPV is associated with increased thrombotic tendency.
Common scenarios explained
"My doctor said I'm slightly anemic": Usually means hemoglobin is 10–12 g/dL (women) or 12–13.5 g/dL (men). Check MCV — if low, likely iron deficiency (most common). If high, check B12 and folate.
"My white count is a little high": If WBC is 11,000–14,000 with high neutrophils, it is usually a recent infection, stress, or inflammation. One elevated reading is rarely concerning; a persistently elevated count deserves investigation.
"My platelets are borderline low": If 130,000–150,000 with no symptoms, it is often normal variation or very mild reduction. Recheck in 3 months. If dropping on serial tests, investigate.
How Merios helps
Upload your CBC results to Merios and we extract every value — RBC, hemoglobin, hematocrit, MCV, WBC with differential, platelets, and more. Track them over time, see trends across multiple blood draws, and understand which changes are noise and which are signal. Pair it with your Apple Watch data for the complete picture.
This article is for informational purposes only and does not constitute medical advice. Discuss abnormal CBC results with your physician.