Complete Blood Count (CBC): How to Read Your Report
A complete blood count, usually written CBC or CP on a Pakistani report, measures the three families of cells in your blood: red cells, which carry oxygen; white cells, which fight infection; and platelets, which stop bleeding. It needs one small tube of blood, no fasting, and results are usually ready the same day. The red cell section, led by haemoglobin, tells you whether you are anaemic and the MCV gives the first clue as to why — a low MCV usually points to iron deficiency or to thalassaemia trait, both common in Pakistan. The white cell section rises in most bacterial infections and in inflammation, and often stays normal or falls in viral illness and in typhoid. Platelets fall in dengue, in malaria and in several other conditions, and a falling trend matters more than any single figure. A value printed just outside the range is common and frequently means nothing: reference ranges are set so that roughly one healthy person in twenty falls outside them, and results vary between laboratories, so always read the range printed beside your own result rather than one from the internet. What matters is the size of the abnormality, whether more than one line is affected, whether it is changing between tests, and how you actually feel. A CBC never diagnoses a condition by itself. Take the report to the doctor who ordered it, and seek care the same day if you have a fever with a very low white cell count, heavy or spontaneous bleeding, a very low platelet count, or breathlessness and chest pain with severe anaemia.
Health writers · Aslam Clinic
What the test is
One small tube of blood, taken from a vein in the arm into a purple-topped bottle, is run through an automated analyser that counts and sizes the cells. No fasting is needed and it can be taken at any time of day. Most laboratories in Pakistan report it within a few hours, and it is one of the cheapest tests on the menu, which is exactly why it is ordered so often — for fever, for tiredness, before surgery, in pregnancy, and as part of a general check.
Some reports show a slide examined by eye as well, described as a peripheral smear or blood picture. That is a person looking at the shape of the cells rather than a machine counting them, and it adds information the counter cannot give — the shape of red cells, immature white cells, or clumped that made the machine undercount.
The report, line by line
| Line on the report | Typical adult range | What it measures | What an abnormal value often suggests |
|---|---|---|---|
| Haemoglobin (Hb) | Men 13.0-17.0 g/dL; women 12.0-15.0 g/dL | How much oxygen-carrying protein the blood holds. | Low means — commonly iron deficiency, blood loss, thalassaemia trait or disease. High can mean , smoking, lung disease or living at altitude. |
| Red cell count (RBC) | Men 4.5-5.9; women 4.1-5.1 million per microlitre | The number of red cells. | Interpreted with Hb and MCV rather than alone. A high count with a low MCV raises the possibility of thalassaemia trait. |
| Haematocrit / PCV | Men 40-52 per cent; women 36-46 per cent | The proportion of blood volume that is red cells. | Moves with haemoglobin. Rises with and is watched closely in dengue, where a rising figure signals fluid leaking out of the vessels. |
| MCV | 80-100 fL | The average size of a red cell. The single most useful clue on the report. | Low points to iron deficiency or thalassaemia trait. High points to vitamin B12 or folate deficiency, alcohol, liver disease or an underactive . |
| MCH and MCHC | MCH 27-32 pg; MCHC 32-36 g/dL | How much haemoglobin each red cell carries, and how concentrated it is. | Both fall in iron deficiency and in thalassaemia, alongside a low MCV. |
| RDW | 11.5-14.5 per cent | How much red cells vary in size from one another. | Usually raised in iron deficiency, and usually normal in thalassaemia trait. That contrast is one of the ways the two are told apart. |
| Total white cells (TLC or WBC) | 4.0-11.0 thousand per microlitre | The infection-fighting cells, all types added together. | Raised in many infections, , steroid treatment and stress. Low in many viral illnesses, in typhoid, in dengue and with some medicines. |
| Neutrophils | 40-75 per cent of white cells | The cells that deal with bacteria. | High with bacterial infection and inflammation. A very low count leaves a person vulnerable to serious infection and needs urgent attention. |
| Lymphocytes | 20-45 per cent | The cells that deal with viruses and make . | Often relatively high in viral illness and in tuberculosis. Low in some infections and with steroids. |
| Monocytes | 2-10 per cent | Scavenging cells. | Raised in some long-running infections, including tuberculosis, and in recovery from infection. |
| Eosinophils | 1-6 per cent | Cells involved in allergy and in parasite infection. | Raised in allergy, , and worm infestation — all common here, which is why this line is checked more often in Pakistan than in Europe. |
| Platelets | 150-450 thousand per microlitre | The fragments that plug a bleeding vessel. | Low in dengue, malaria, viral fevers, some medicines, alcohol and liver disease. Raised in iron deficiency, infection and inflammation, and occasionally in more serious conditions. |
Red cells: the anaemia question
means the blood carries less oxygen than it should. The WHO defines it in non-pregnant adults as a below 13 g/dL in men and below 12 g/dL in women, with a lower threshold of 11 g/dL in pregnancy and in young children. It is extremely common in Pakistan: national survey data has repeatedly found around four in ten women of reproductive age and around half of children under five to be anaemic, mostly from iron deficiency.
The symptoms are unglamorous and easy to dismiss — tiredness that sleep does not fix, breathlessness on stairs, poor concentration, headache, cold hands, brittle nails, hair fall, and in severe cases and chest pain. Pale inner eyelids and pale palms are the classic signs, though they only show up once the anaemia is well established.
The MCV then splits the possibilities. A low MCV with a low haemoglobin usually means iron deficiency — from diet, from heavy periods, from a bleeding ulcer or from hookworm — or it means thalassaemia trait, which perhaps one Pakistani in twenty carries. The two look similar on a CBC and are treated completely differently, so the difference matters. A doctor will usually check ferritin, and may use the ratio of MCV to red cell count, known as the Mentzer index, as a first pointer: below about 13 leans towards thalassaemia trait and above 13 towards iron deficiency. It is a hint, not a diagnosis, and confirming thalassaemia trait requires haemoglobin electrophoresis. A high MCV points instead to vitamin B12 or folate deficiency, to alcohol, to liver disease or to .
White cells: what the differential is telling you
A raised total white cell count with a high proportion of neutrophils is the classic pattern of a infection, and it is also produced by , by injury, by steroids, by pregnancy and by simple physical stress — a count of 12 or 13 in a frightened child having blood taken proves very little on its own.
A normal or low count with a relative rise in lymphocytes is the pattern of a viral illness. Typhoid is the exception worth knowing in this country: it classically produces a normal or low white cell count despite being a serious bacterial infection, so a normal count does not rule it out. Dengue also drops both white cells and platelets. Raised eosinophils suggest allergy or worms rather than infection in the usual sense, and are common enough here to be worth acting on.
Platelets, and the dengue season
are what stop you bleeding. Between roughly 150 and 450 thousand is the usual range, and mild reductions to 100 or 120 are common during and after viral illness and usually recover on their own. Below about 50 the risk of bleeding starts to matter; below about 20 it matters a great deal, and that is a hospital-level number.
During dengue season the platelet count is the figure everyone watches, and it is watched for the wrong reason. The count on its own is a poor guide to who becomes seriously ill. What actually predicts trouble is the combination of a falling platelet count with a rising haematocrit — meaning fluid is leaking out of the blood vessels — together with warning signs such as severe abdominal pain, persistent vomiting, bleeding, lethargy or restlessness. Platelet transfusion is not given for a number alone in an otherwise stable person; papaya leaf extract and similar remedies have no reliable evidence behind them, and relying on them while ignoring the warning signs is how people arrive at hospital late.
One artefact worth knowing: if the sample clots slightly, or the platelets clump in the anticoagulant used in the tube, the analyser undercounts them. If a very low platelet count turns up in someone with no bruising and no bleeding, a repeat sample and a look at the slide is a reasonable next step before anyone panics.
What out of range does and does not mean
| Pattern on the report | Common explanations | What usually happens next |
|---|---|---|
| One value marked slightly high or low, and you feel well | Normal variation. Ranges are built so about one healthy person in twenty falls outside them. | Often nothing, or a repeat in a few weeks. Context and how you feel decide. |
| Low Hb, low MCV, high RDW | Iron deficiency is the usual answer. | Ferritin, and a search for where the iron is going — periods, diet, gut bleeding, hookworm. |
| Low or borderline Hb, very low MCV, normal RDW, normal or high red cell count | Thalassaemia trait is a real possibility, especially with a family history. | Ferritin and haemoglobin electrophoresis. Important before marriage and before pregnancy. |
| High white cells with high neutrophils | Bacterial infection, , steroids, or stress. | Treatment aimed at the cause, not at the number. A repeat count after recovery. |
| Low white cells with fever | Viral illness, typhoid, dengue — or a drug affecting the marrow. | Same-day assessment if it is very low, and a medicine review. |
| Low platelets during a fever | Dengue and malaria are the first two to exclude in season. | Repeat counts, and haematocrit trend, and warning-sign monitoring. |
| Two or three cell lines low together | Needs proper assessment — the marrow, a deficiency, or a serious illness. | Prompt referral, usually with a smear and further blood tests. |
| Persistently raised platelets with no infection | Iron deficiency and inflammation are the common causes. | Investigation of the cause; in an older adult it may prompt a wider look. |
Three habits make a CBC far more useful. Keep your old reports, because a trend answers questions a single result cannot. Use the same laboratory where you can, so the ranges and the analyser are consistent. And take the report back to whoever ordered it, together with the that prompted it — a number read without the person attached to it is how healthy people end up on unnecessary treatment and unwell people end up reassured.
When to see a doctor
- Any of the emergency findings listed near the top of this article, on the same day.
- below the range, at any level, in a man or in a woman past menopause — the cause needs finding.
- Anaemia that has not corrected after two to three months of the treatment you were given.
- A low platelet count that is falling on repeat testing, or any bleeding or unexplained bruising.
- A white cell count that stays abnormal after the illness that prompted the test has passed.
- Any abnormal count alongside weight loss, night sweats, persistent fever, bone pain or lumps in the neck, armpit or groin.
- Before a pregnancy or a marriage where thalassaemia trait is a possibility — see also our article on HbA1c if diabetes is being screened for at the same time.
Common questions
Still not sure what to do?
Reading about a symptom only goes so far. A doctor who can ask you questions and examine you will get further in ten minutes than any article can.
