Key points
- Normal ranges differ from one person to another; a value slightly above or below the range is also seen in healthy people [1].
- Changes in white cells often have a simple cause: infection, stress, exercise, smoking, obesity, pregnancy or a medicine [2].
- Slightly low white cells or neutrophils are inherited and harmless in many people of Middle Eastern and African origin, and do not raise the risk of infection [3, 4].
- Unexplained iron-deficiency anaemia at any age, and any anaemia after the age of 60, should be checked for hidden bleeding from the bowel [7, 12].
- Show your doctor promptly if the blood film shows immature cells, if values are very high or very low, or if several lines of the test change at the same time [2, 3].
How to read a CBC with differential
A complete blood count (CBC) measures the number of white cells, red cells and platelets, the amount of haemoglobin and the size of the red cells [1]. The "differential" (Diff) shows which types of white cell are present.
Three tips for reading the report:
- Look at your own laboratory's range. Normal ranges are set from the results of large numbers of healthy people and depend on age, sex, ethnic background and even the day of the test [1].
- Look at the absolute count, not just the percentage. Many reports give the white cell types as percentages. The absolute count is the total white cell count multiplied by that percentage. For example, if the white cell count is 10,000 and monocytes are 12%, the monocyte count is 1,200, which is high [2]. To work out your neutrophil count, you can use the ANC calculator.
- The trend matters more than a single number. If a value is slightly abnormal, your doctor will usually repeat the test and compare it with your earlier results [2].
| Test line | What it shows | Approximate range in adults |
|---|---|---|
| White blood cells (WBC) | All white cells, the body's defence cells | 4,500 to 11,000 per microlitre [2] |
| Neutrophils (Neut) | The most common white cell; rises in bacterial infections [2] | 40% to 60% of white cells; above 7,000 is high and below 1,500 is low [2, 3] |
| Lymphocytes (Lymph) | Rise in viral infections [2] | 20% to 40%; above 4,500 or above 40% is high [2] |
| Monocytes (Mono) | Rise in some infections and autoimmune diseases [2] | 2% to 8%; above 880 or above 8% is high [2] |
| Eosinophils (Eos) | Rise in allergies, asthma and parasite infections [2] | 1% to 4%; above 500 is high [2] |
| Basophils (Baso) | Few in number; a rise on its own is rare [2] | 0.5% to 1%; above 100 is high [2] |
| Haemoglobin (Hb) | The oxygen-carrying protein; a low level means anaemia [6] | Anaemia: below 13 in men and below 12 in non-pregnant women (grams per decilitre) [6] |
| MCV | The average size of the red cells [7] | 80 to 100 femtolitres; lower means small red cells and higher means large red cells [7] |
| Platelets (PLT) | Cells that help stop bleeding [9] | Below 150,000 is low [9] and above 400,000 is high [10] |
The range printed on your own laboratory's report is what counts; these numbers are approximate and differ for children and in pregnancy [2, 6].
What do low neutrophils or a low white cell count mean in a blood test? Is it dangerous?
When the white cell count is low, the most important number is the neutrophil count: the cells that fight bacteria. A neutrophil count below 1,500 per microlitre is called "neutropenia": 1,000 to 1,500 is mild, 500 to 1,000 is moderate and below 500 is severe [3].
Common causes: viral infections, medicines and radiotherapy. Other causes are autoimmune diseases, nutritional deficiencies and sometimes cancers [3]. This is why your doctor will usually repeat the test a few weeks apart before drawing any conclusion [3].
Inherited, harmless low neutrophils: in many people of African or Middle Eastern origin, the neutrophil count is always slightly below the usual range. In a study in the United Arab Emirates, about 1 in 10 Arab people had this [3], and in a study in Bahrain, about 1 in 7 patients with breast cancer [4]. In these people the neutrophil count is usually between 1,000 and 1,500, they do not get more infections than others, and if the rest of the test and the examination are normal, they need no further tests [3]. If your white cell count has always been "a little low", tell your doctor, especially before chemotherapy [3, 4].
When is it dangerous? A neutrophil count below 500, or low neutrophils with fever, mouth ulcers, repeated infections, swollen lymph nodes or spleen, or low haemoglobin or platelets, needs urgent assessment by a blood specialist [3]. If you are having chemotherapy, read low blood counts and preventing infection.
What does a high white blood cell count mean?
A white cell count above 11,000 is considered high, and most often it is the neutrophils that have increased [2]. Common and usually harmless causes [2]:
- Infection, especially bacterial infection
- Physical or emotional stress, surgery, injury and hard exercise; the white cell count can rise within hours
- Smoking, obesity and pregnancy
- Medicines: steroids (such as prednisolone), lithium, inhalers that open the airways (such as salbutamol) and injections that boost white cells
- Long-term inflammatory diseases such as rheumatoid arthritis or inflammatory bowel disease, and removal of the spleen
These causes usually raise the white cell count to about 30,000 at most. A count above 100,000 is almost always due to leukaemia or a similar bone marrow disease [2]. See the warning signs in what leukaemia looks like on a blood test (CBC).
What do high lymphocytes mean in a blood test?
A lymphocyte count above 4,500 per microlitre, or above 40% of white cells, is considered high [2]. Viral infections, whooping cough, syphilis and allergic reactions raise lymphocytes, and sometimes leukaemia or lymphoma. A high lymphocyte count is more often harmless in children than in adults [2].
In adults, if lymphocytes stay high for months with no clear cause, your doctor may ask for a flow cytometry test to see whether the cells are all of one type. For a diagnosis of chronic lymphocytic leukaemia (CLL), B lymphocytes must be at least 5,000 and stay high for at least 3 months [11]. Even when fewer cells of one type are found (monoclonal B-cell lymphocytosis), only 1 to 2 in 100 people a year come to need treatment [11].
High lymphocytes and low neutrophils
This combination is seen with viral infections, because viruses both raise lymphocytes and are among the most common causes of low neutrophils [2, 3]. Sometimes only the lymphocyte percentage is high and the absolute count is normal, so work out the absolute count [2]. If it is still there after a few weeks, or comes with fever, mouth ulcers or low haemoglobin and platelets, see a doctor [3].
High neutrophils and low lymphocytes
This pattern is the body's usual response to stress, bacterial infections, inflammation and some medicines such as steroids [2, 5]. The neutrophil-to-lymphocyte ratio rises in many different illnesses; it is sensitive but not specific to any one disease, and it usually falls as the illness gets better [5].
High monocytes and everything else normal: should I worry?
A monocyte count above 880 per microlitre or above 8% is considered high [2]. Causes include Epstein-Barr virus infection (glandular fever), tuberculosis and fungal infections, autoimmune diseases, removal of the spleen, some other infections and sometimes cancers [2]. If the rest of the test is normal and you feel well, your doctor will usually repeat the test first [2]. Monocytes that stay high for months without a cause are worth checking by a blood specialist [2]; read about this in what leukaemia looks like on a blood test (CBC).
Haemoglobin and MCV: where does anaemia come from?
The World Health Organization defines anaemia in adults as a haemoglobin below 13 in men and below 12 in non-pregnant women (grams per decilitre). In pregnancy, in smokers and in people living at high altitude these numbers are different [6]. The size of the red cells (MCV) helps to find the cause of anaemia [7]:
- Low MCV (below 80): the most common causes are iron deficiency and thalassaemia trait (being a thalassaemia carrier). In thalassaemia trait, the red cell count is usually normal or slightly high. The first test to find the cause is ferritin (the iron store), and thalassaemia is identified by haemoglobin electrophoresis [8]. If you have been told before, for example in a premarital or pregnancy screening test, that you carry thalassaemia, tell your doctor; the small red cells of thalassaemia carriers are different from iron deficiency, and these tests tell them apart [8].
- High MCV (above 100): vitamin B12 or folic acid deficiency, which sometimes comes from heavy drinking, problems with absorption in the gut, or long-term use of stomach acid medicines such as omeprazole or the diabetes medicine metformin. If unusual changes are seen on the blood film, a blood specialist needs to check them [7].
Take iron-deficiency anaemia seriously. In adults, unexplained iron deficiency can come from hidden bleeding in the stomach or bowel [7, 8]. The national guideline in England advises a stool test for hidden blood for every adult with iron-deficiency anaemia, and for any anaemia after the age of 60 [12]. Read: can a blood test detect cancer?
What do low or high platelets mean?
Low platelets (below 150,000): often found by chance on a CBC. As long as platelets are above 50,000, there are usually no symptoms. Between 10,000 and 30,000, even a small knock may cause bleeding, and below 5,000 bleeding may happen on its own, which is an emergency [9]. Sometimes the platelets have only clumped together in the test tube and the count is wrongly reported as low; repeating the test in a different tube clears this up [9]. Common causes: medicines (such as heparin, the epilepsy medicines carbamazepine and phenytoin, and the antibiotic vancomycin), alcohol and liver disease, viral infections, autoimmune platelet disease (ITP), pregnancy and B12 or folic acid deficiency; less often, bone marrow diseases [9]. If the drop is mild and you have no symptoms, the test is usually repeated 1 to 4 weeks later [9].
High platelets (above 400,000): most people with high platelets do not have cancer. But in people aged 40 or over, especially when platelets are still high on a second test, it is worth checking; in a large study, lung and bowel cancer were found more often in these people [10].
Why would I be referred to a haematologist?
Being referred to a blood specialist does not mean you have cancer. Your doctor refers you when the cause of the changes is not clear or a blood disease needs to be ruled out [2]. Common reasons for referral:
- A change that persists on repeat tests with no cause found [2, 9]
- Two or three lines of the test low at the same time (white cells, haemoglobin, platelets) [3]
- Immature or abnormal cells on the blood film [2, 7]
- A very high white cell count, or lymphocytes or monocytes that stay high for months [2, 11]
- Neutrophils below 500 or very low platelets [3, 9]
What happens at a haematology appointment?
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Sometimes a bone marrow sample
If the blood film or other tests raise the possibility of a bone marrow disease, a small sample of bone marrow is taken [9]. More: which tests come after an abnormal CBC?
When should I see a doctor?
Contact your doctor the same day or go to an emergency department if:
- You have low neutrophils and develop a fever of 38°C or higher, shivering or mouth ulcers [2, 3]
- Your neutrophil count is below 500 [3]
- Your platelet count is below 20,000, or you have bleeding on its own from the gums or nose, blood in your urine or black stools [9]
- The blood film report mentions "blasts" or immature cells, or the white cell count is above 100,000 [2]
- Your haemoglobin is below 8 (severe anaemia) [6], or you have shortness of breath, chest pain or fainting with anaemia
See a doctor within a few days if a change in your blood test comes with lasting tiredness, night sweats, unexplained weight loss, bruising, tiny red spots under the skin or swollen lymph nodes [2, 12].
If you suddenly feel very unwell, for example bleeding will not stop or you are confused, call your local emergency number.
Frequently asked questions
My CBC is slightly high or low; should I worry?
Does smoking affect CBC results?
Yes. Smoking raises the white cell count [2] and also keeps haemoglobin slightly higher; this is why the World Health Organization uses a higher anaemia cut-off for smokers [6]. Read: quitting smoking and cancer risk.
Are CBC results different in pregnancy?
Can a CBC detect cancer?
A CBC helps to diagnose blood cancers, especially leukaemia, but it does not show most other cancers, and a normal result does not rule cancer out [1]. Read: can a blood test detect cancer? and what leukaemia looks like on a blood test (CBC).
My blood counts have dropped during chemotherapy; what should I do?
Low blood counts are expected during chemotherapy, and your team plans your tests around them. During this time, report a fever of 38°C or higher to your team straight away. Full guide: low blood counts and preventing infection.
Related pages
CBC interpretation notes (for doctors)
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Leukocytes. Normal adult WBC 4.5 to 11.0 × 109/L; neutrophilia above 7.0, lymphocytosis above 4.5 (or above 40%), monocytosis above 0.88 (or above 8%), eosinophilia above 0.5 and basophilia above 0.1 × 109/L; use absolute counts. Reactive leukocytosis is typically 11 to 30 × 109/L, and a WBC above 100 × 109/L is almost always due to leukaemia or a myeloproliferative neoplasm. Non-malignant causes of neutrophilia: infection, stress, exercise, smoking, obesity, pregnancy, corticosteroids, beta agonists, lithium, epinephrine, G-CSF, chronic inflammation, asplenia and marrow recovery. Red flags: WBC above 30 × 109/L, predominantly immature cells, monomorphic lymphocytosis, low haemoglobin, abnormal platelets, fever, night sweats, weight loss, bruising, lymphadenopathy, petechiae or hepatosplenomegaly [2]. A normal NLR is 1 to 2, and values above 3 or below 0.7 in adults are abnormal; sensitive but non-specific [5].
Neutropenia, BEN and DANC. Neutropenia: ANC below 1.5 × 109/L (mild 1.0 to 1.5, moderate 0.5 to 1.0, severe below 0.5). Benign ethnic neutropenia (BEN) occurs in people of African, Middle Eastern and Caribbean descent; reported prevalence 25% to 50% in Africans, 10.7% in Arabs, 11.8% in Yemenite Jews and below 1% in white people in the US; ANC usually 1,000 to 1,500/µL, with no increased infection risk. When the ANC is low on at least three samples at least two weeks apart and there is no secondary cause, other cytopenia, splenomegaly or lymphadenopathy, no further work-up is needed; Duffy phenotyping if required. ANC 500 to 1,000: outpatient work-up for secondary causes; ANC below 500, recurrent or severe infections, fevers, oral ulcers, organomegaly, lymphadenopathy or another cytopenia: urgent haematology referral [3]. Among 493 patients with breast cancer in Bahrain, 72 (14.6%) had presumed Duffy-null associated neutrophil count (DANC, the new name for BEN; median ANC 1.2 × 103/µL); treatment delays and discontinuations were more common (P < 0.001) and were not reduced by prophylactic filgrastim, all responded to filgrastim, only one had febrile neutropenia, and DANC or treatment delay had no effect on OS or PFS [4].
Anaemia and MCV. WHO 2024 (15 to 65 years): men below 130 g/L and non-pregnant women below 120 g/L; pregnancy: first and third trimester below 110 and second trimester below 105 g/L; severe below 80 g/L; adjust for altitude and smoking [6]. Microcytosis (MCV below 80 fL): the most common causes are iron deficiency and thalassaemia trait; ferritin is the first test, and iron deficiency is likely with ferritin below 15 ng/mL (or below 50 with chronic inflammation); in beta-thalassaemia trait the RBC count is high-normal and HbA2 slightly raised, and coexisting iron deficiency lowers HbA2 [8]. Macrocytosis (MCV above 100 fL): blood film and reticulocyte count first; B12 or folate deficiency (alcohol, malabsorption, long-term PPI, H2 receptor antagonist or metformin use); smear abnormalities suggest MDS or malignancy and warrant haematology consultation [7]. NICE NG12: FIT to guide referral in iron-deficiency anaemia and in people aged 60 or over with anaemia even without iron deficiency [12].
Platelets. Thrombocytopenia below 150 × 109/L (mild 70 to 150, severe below 20); above 50 usually asymptomatic, 10 to 30 bleeding with minimal trauma, and below 5 spontaneous bleeding and a haematological emergency. Incidental asymptomatic thrombocytopenia of 50 to 150: repeat in 1 to 4 weeks; pseudothrombocytopenia (EDTA-dependent clumping): repeat with a non-EDTA anticoagulant. In 10-year follow-up of 217 people with platelets of 100 to 150, counts normalised or stayed stable in 64%, the probability of ITP was about 7%, of autoimmune disease about 12%, and MDS was diagnosed in 2%. Isolated thrombocytopenia over the age of 60: evaluate for MDS and lymphoproliferative disorders [9]. Thrombocytosis (above 400 × 109/L) at age 40 or over: 1-year cancer incidence 11.6% in men and 6.2% in women, and 18.1% and 10.1% with a second raised count within 6 months [10].
Lymphocytosis. CLL: 5 × 109/L or more B lymphocytes, sustained for at least 3 months, with clonality on flow cytometry; below that without lymphadenopathy, organomegaly, cytopenias or symptoms: MBL, progressing to CLL requiring treatment at 1% to 2% per year [11].
Related cancer types
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References
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Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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