White Blood Cell Count
The total number of white blood cells, the immune cells that fight infection, in a small sample of your blood.
AI-verified against cited sources. Awaiting expert reviewAlso called WBC, WCCLOINC 6690-2
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What it is
White blood cells (leukocytes) are made in your bone marrow. They travel through your blood to fight germs and clear away damaged cells. The WBC count is the total of all five main types: neutrophils, lymphocytes, monocytes, eosinophils and basophils. It is a routine part of a complete blood count (CBC). A separate result called the differential shows how many of each type you have.
Why it matters
Your white cell count tends to rise when your body is responding to an infection, inflammation or stress. It can fall when the bone marrow or immune system is under strain. One total number can't show which cell type changed or why, so clinicians read it with the differential, your symptoms and your past results. A count that is a little outside your lab's range is common and is often temporary.
If it’s low
A low count (leukopenia) can happen with viral infections, some medicines and other conditions that slow the bone marrow. It can also be a normal variation. Many people of African ancestry, and some people from other groups, have lower white cell counts that are still healthy. Because white cells defend against infection, clinicians pay close attention to which type is low, especially neutrophils.
Common causes
- Viral infections, including a recent cold or flu-like illness
- Medicines such as chemotherapy, and certain others
- Bone marrow damage from infection, disease or cancer treatment
- Autoimmune conditions such as lupus
- HIV and some other infections
- Low vitamin B12 or folate
- Liver disease or an enlarged spleen
- A normal, lower baseline, such as with the Duffy-null gene variant
What can help
- Ask your clinician whether to repeat the test and look at the differential, especially the neutrophil count
- Ask whether your ancestry could explain a lower count
- Review your medicines and supplements with your clinician
If it’s high
A high count (leukocytosis) most often means your body is responding to something. Common reasons are an infection, inflammation, a hard workout just before the draw, smoking, stress or a medicine such as a steroid. Pregnancy also raises it. Less often, a count that stays high points to a blood or bone marrow condition, which is why clinicians look at which cell types are up.
Common causes
- Infection, from bacteria or viruses
- Inflammation, such as rheumatoid arthritis and other inflammatory conditions
- Allergic reactions
- Tissue injury, such as a burn or recent surgery
- Smoking
- Physical or emotional stress, including hard exercise just before the blood draw
- Some medicines, including steroid medicines
- Pregnancy
- Less often, blood conditions such as leukemia
What can help
- Ask your clinician whether a repeat count in a few weeks makes sense, especially if you were sick or exercising hard before the draw
- If you smoke, ask about support to quit, since smoking is linked to higher white cell counts
- Tell your clinician about all medicines and supplements you take, since some change white cell counts
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 3.8–10.8 ×10³/µL. Source: Quest Diagnostics, Labcorp, Oregon Health & Science University, Te Whatu Ora Health New Zealand, Waikato, American Board of Pathology, University of Iowa Hospitals & Clinics, Journal of Clinical Pathology, Hematology Reports. Labs treat below 2 ×10³/µL as urgent.
- Adults (this one applies)3.8–10.8 ×10³/µL
Sources: Quest Diagnostics, Labcorp, Oregon Health & Science University, Te Whatu Ora Health New Zealand, Waikato, American Board of Pathology, University of Iowa Hospitals & Clinics, Journal of Clinical Pathology, Hematology Reports
See WBC by age and sex, with the U.S. survey numbers where they exist.
If this applies to you
WBC means a little more for some people. Open the one that fits you.
Taking methotrexate
Methotrexate can lower the blood cells made in the bone marrow. White cells, which fight infection, are counted at every routine check, and the BSR says a gradual fall is worth noticing as well as a single low result.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore WBC by age and sex: every percentile as a table, with a download.
What can affect your result
- Age: children's counts are higher than adults'
- Pregnancy: counts usually rise
- Ancestry: people of African ancestry, and people with the Duffy-null variant, often have lower counts
- Smoking raises the count
- Recent hard exercise, physical stress or emotional stress
- Medicines: steroid medicines tend to raise it and chemotherapy lowers it
- Recent infection or ongoing inflammation
- Sample handling: the blood should be drawn into the right tube and tested promptly
- Hard exercise, acute stress and steroid medicines can raise the count for hours to days without any infection. Smoking tends to keep it somewhat higher.
- Some automated counters can mistake nucleated red cells, clumped platelets, cryoglobulins or red cells that resist lysis for white cells. Labs usually flag these and correct or repeat the count.
- A clotted sample, a sample diluted with IV fluid, the wrong type of tube, or a sample kept in the refrigerator can give unreliable counts. Labs reject or recollect these.
- Chemotherapy and some other medicines lower the count.
Can change within hours with infection, stress, exercise or steroid medicines, and usually settles within days to a few weeks once the cause passes.
When to talk to a clinician
Labs phone a clinician right away when the count is 2.0 ×10³/µL or lower, or 40 ×10³/µL or higher (ARUP's urgent-call limits; other labs use slightly different limits). Contact a clinician the same day if your count is low and you have a fever of 100.4 °F (38 °C) or higher, chills or other signs of infection. Call 911 or your local emergency number if you feel faint or confused, or have trouble breathing.
Questions you could ask
- How does my white cell count compare with my past results?
- Could a recent illness, hard exercise, smoking or a medicine explain my result?
- Should we look at the differential or repeat the count?
- Could my ancestry or a medicine explain a lower count?
- Should we look at my neutrophil count or repeat the test?
Questions people ask
My WBC is slightly high and I feel fine. Should I worry?
A mildly high count is common and often has a harmless cause, such as a recent cold, hard exercise, smoking, stress, a steroid medicine or pregnancy. Your clinician may repeat the test or check the differential to see which cell types are up. If the count stays high without a clear reason, that is worth discussing.
Can my WBC be low and still be healthy?
Yes. Some people, including many people of African ancestry, naturally have lower white cell counts. This is often linked to a harmless inherited trait called Duffy-null. What matters is the pattern over time, which cell types are low and how you feel. Your clinician can put your result in context.
What is the difference between the WBC and the differential?
The WBC is the total number of white cells. The differential splits that total into the five main types, as percentages or as absolute counts. A total in the usual range can hide a high or low count of one type, which is why labs often report both.
How do I convert white blood cell units?
×10³/µL, K/µL, thou/mm³ and ×10⁹/L are the same number, so 7.5 in one is 7.5 in the others. If your report shows cells per µL or per cu mm (for example 7,500 /cumm), divide by 1,000 to get ×10³/µL.
Show the science and sources
Units
- 1 ×10³/µL = 1 ×10³/µL
- 1 ×10³/µL = 1 ×10⁹/L
- 1 ×10³/µL = 1000 cells/µL
Is a change real?
WBC naturally varies about 10.01% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 31% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters (Coskun A et al., EFLM WG-BV).
For clinicians and researchers
Automated analyzers count leukocytes after red cells are lysed, using electrical impedance, optical scatter or fluorescence flow cytometry. 1 ×10³/µL equals 1 ×10⁹/L and 1,000 cells/µL. Nucleated red cells, platelet clumps, cryoglobulins and lysis-resistant red cells can be counted as leukocytes; most analyzers flag these and correct or repeat the count. In the sources used, adult lower limits run 3.4–4.0 and upper limits 10.5–11.0 ×10³/µL. Healthy people of African ancestry often have lower total WBC and neutrophil counts (Bain 1996), and the Duffy-null phenotype, caused by the ACKR1 promoter variant rs2814778, is linked to lower but clinically benign WBC and absolute neutrophil counts (Barouqa 2026). A 2026 single-center study of 122 healthy Duffy-null adults reported 95% reference intervals of 2.43–7.05 ×10³/µL for WBC and 1.01–4.34 for ANC. Interpretation depends on the differential, especially the absolute neutrophil count, and on the trend within the same person. Counts are higher in children and rise in pregnancy and labor. Indian and some other labs report cells/cu mm, so 7,500/cumm is 7.5 ×10³/µL.
LOINC 6690-2 (primary), 26464-8, 804-5. Specimen: whole-blood.
Sources
- White Blood Cell Count (WBC), test 937, Quest Diagnostics
- CBC, Platelet, No Differential (test 028142), sample report, Labcorp (2020)
- Heme Reference Ranges (updated 6/5/18), Oregon Health & Science University (2018)
- CBC reference intervals (HEM-2597.01), Te Whatu Ora Health New Zealand, Waikato (2024)
- Hematopathology reference ranges, American Board of Pathology
- CBC (Complete Blood Count), Pathology Handbook, University of Iowa Hospitals & Clinics
- Ethnic and sex differences in the total and differential white cell count and platelet count, Journal of Clinical Pathology (1996)
- Establishing Reference Intervals for White Blood Cell and Absolute Neutrophil Counts in Duffy Null Individuals, Hematology Reports (2026)
- Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
- Appendix 1: Critical Value List, The University of Chicago Medical Center Laboratories
- Diagnostic Laboratories: Critical Values, Houston Methodist
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.