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Absolute Count of White Blood Cells (WBC) in Whole Blood

Published: August 9, 2026Updated: August 16, 2026

This test measures the total number of white blood cells in your blood, which helps assess your immune system's strength and detect infections or other conditions.

Quick summary

["Your immune health and risk for infections may be evaluated with this simple blood test."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
9771-7
Short code
CD5CD20
Synonyms
CD5+CD20+ Cells # WBC
Category
chemistry
Sample
serum
Container
EDTA (lavender-top) blood collection tube for flow cytometry; sodium heparin tube is an acceptable alternative
Units
N/A
Ref low
4.5
Ref high
11
Critical range
2 N/A – 30 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Flow cytometry using fluorescently labeled monoclonal antibodies against CD5 and CD20 surface markers, followed by absolute count calculation using leukocyte count
CPT
86356 (per marker, may require multiple codes such as 86355, 86356, 86357, 86359 for immunophenotyping panels)
SNOMED
395124008
Specimen volume
3-5 mL whole blood in EDTA tube; minimum 1 mL for pediatric or limited samples
Stability
Specimen should be processed within 24-48 hours of collection when stored at room temperature (18-25°C); viability decreases significantly after 48 hours. Refrigeration at 4°C may extend viability slightly but is generally not recommended for immunophenotyping.
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
24–72 hours
Order
routine

Why This Test Is Done

Doctors may order a WBC count to diagnose or monitor conditions like infections (bacterial, viral, or fungal), blood disorders (such as leukemia), autoimmune diseases, or to check for signs of inflammation. It can also be used during pregnancy, before surgery, or to evaluate symptoms like fever, fatigue, or unexplained weight loss.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or hand to draw blood. If you’re taking blood from your vein, you might feel a slight pinch or discomfort, but it usually lasts only a few seconds. If you’re concerned about needles, let your healthcare provider know.

What the Test Results Mean

Results are typically reported as a total WBC count (in cells per microliter, or µL). While reference ranges vary by lab, a lower than expected count may indicate immune suppression, while a higher count could signal infection, inflammation, or other health issues. Your doctor will interpret results in relation to your overall health and symptoms.

Common Conditions Affecting WBC Counts

Low WBC counts (leukopenia) might occur due to medications, autoimmune diseases, or severe infections, while high WBC counts (leukocytosis) can result from infections, stress, or certain cancers. Chronic conditions like diabetes or kidney disease may also influence WBC levels.

Reference range

Adult: 4.5-11.0 x 10^9/LN/A

Specimen: serum

No special patient preparation required. Fasting is not necessary.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

WBC Count

Frequently asked questions

How often do I need this test?
Your doctor will determine how often you need this test based on your health status, symptoms, or treatment plan. Some people may need it once a year, while others may require it more frequently if they have ongoing health concerns.
Can I eat or drink before this test?
You can eat and drink normally before this test unless your doctor specifies otherwise. Typically, fasting is not required for a WBC count.
What are the risks or side effects of this blood draw?
The most common side effect is a small bruise, redness, or slight pain at the injection site. Rarely, there may be a slight swelling or bleeding. If you experience excessive bleeding, severe pain, or signs of infection (like fever or redness spreading), contact your healthcare provider immediately.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy