CBC test — what each number on your report means · DiagnoHouse

A CBC report has about 15 numbers on it. Even the doctor's note that follows usually doesn't explain each one. Here's what every line means, in plain words, with the ranges that most Indian labs use.

The three groups of cells

Your blood has three families of cells:

Red blood cells carry oxygen. Their main protein is haemoglobin.
White blood cells fight infection. There are five sub-types, each doing a different job.
Platelets help blood clot.

A CBC counts how many you have of each, measures their size and shape, and looks at the relative balance.

Red blood cell numbers

Haemoglobin (Hgb or Hb)

The protein that carries oxygen. Normal range: 13–17 g/dL for men, 12–15 g/dL for women.

Low haemoglobin = anaemia. Most common cause in India is iron deficiency, especially in menstruating women. Other causes: Vitamin B12 deficiency, chronic disease, thalassaemia.
High haemoglobin = uncommon. May suggest dehydration, smoking, or living at high altitude.

RBC Count

Number of red blood cells per microlitre. Normal 4.5–5.9 million/µL (men), 4.0–5.2 million/µL (women).

Usually moves in the same direction as haemoglobin.

Hematocrit (PCV)

The percentage of your blood that is red cells. Normal 40–50% (men), 36–46% (women).

Used together with Hgb and RBC to confirm anaemia.

MCV (Mean Corpuscular Volume)

The average size of your red cells. Normal 80–100 femtolitres.

Low MCV (small cells) — iron deficiency or thalassaemia
High MCV (large cells) — Vitamin B12 or folate deficiency
Normal MCV with low haemoglobin — chronic disease, blood loss, bone marrow problems

MCH and MCHC

How much haemoglobin is in each red cell (MCH) and its concentration (MCHC). Used together with MCV to characterise the type of anaemia.

RDW (Red Cell Distribution Width)

How much variation there is in red cell size. Higher numbers mean more variation — often an early sign of iron deficiency before MCV changes.

White blood cell numbers

Total WBC count

Number of white blood cells. Normal 4,000–11,000 per microlitre.

High WBC (leukocytosis) — bacterial infection, inflammation, stress, steroid use
Low WBC (leukopenia) — viral infection, certain medications, bone marrow problems

The differential

Five sub-types, reported as percentages and absolute counts:

Neutrophils (40–70%) — the front-line bacterial-infection fighters. High in bacterial infection, low in viral infection or some medications.
Lymphocytes (20–40%) — viral-infection and chronic-infection fighters. High in viral illness, TB, some leukaemias.
Monocytes (2–10%) — clean-up cells. High in chronic infection or inflammation.
Eosinophils (1–6%) — allergy and parasite-fighting cells. High in asthma, allergies, worms.
Basophils (0–1%) — small number; rarely abnormal in isolation.

The relative proportions often tell more than the total count. "High WBC with high neutrophils" suggests bacterial infection; "high WBC with high lymphocytes" suggests viral.

Platelets

Number of platelets per microlitre. Normal 150,000–400,000.

Low platelets (thrombocytopenia) — dengue, viral infection, some medications, autoimmune
High platelets (thrombocytosis) — infection, inflammation, iron deficiency, rarely a primary blood disorder

In dengue, platelets are the most-watched number — a falling trend below 100,000 needs daily monitoring, below 20,000 may need transfusion.

MPV (Mean Platelet Volume)

The average size of platelets. Useful for distinguishing different causes of low platelet counts.

What to do with the report

Look at the impression first. Most reports will flag the abnormal values clearly.
Don't panic at a single mildly abnormal value. Normal ranges are statistical — about 5% of healthy people will be slightly outside. If you feel well and a value is borderline, often the right step is a repeat in 3 months.
Look for patterns. Low haemoglobin + low MCV + raised RDW = strong iron deficiency picture. Low haemoglobin + high MCV = Vitamin B12 or folate deficiency. These patterns make the diagnosis far more confidently than a single value.
Take it to your doctor with context. Symptoms, medications, recent illnesses, family history — all change the interpretation. The same CBC means different things in a 25-year-old vegetarian woman vs a 70-year-old man on chemotherapy.

When to repeat

Anaemia: retest haemoglobin 4 weeks after starting iron — should rise by 1 g/dL.
Low platelets during illness: every 24–48 hours until stable.
Routine annual check: once a year is enough if previous CBC was normal.

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Complete Blood Count (CBC)