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White Blood Cell Count with Differential (Serum/Plasma or Whole Blood)

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

This test measures the types and proportions of white blood cells in your blood, helping identify infections, inflammation, or other immune system issues.

Quick summary

["Understanding your immune cell balance can help diagnose and guide treatment for health concerns."]

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

Key facts at a glance

LOINC
30402-2
Short code
WBC # Gast
Synonyms
WBC # Gast
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
2 N/A – 30 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

A white blood cell differential (also called a WBC differential) breaks down the five main types of white blood cells into their individual counts. These include neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each type plays a unique role in your immune response.

Why It’s Done

Doctors may order this test to diagnose infections (like bacterial or viral), autoimmune diseases, allergies, or conditions affecting your bone marrow. It can also help monitor treatment progress for blood disorders or cancer.

Sample Collection and Preparation

Blood is drawn from a vein, typically in your arm. The sample is sent to a lab where it’s analyzed under a microscope to count and identify each type of white blood cell. Sometimes, a blood smear is prepared for closer examination.

Common Reasons for Testing

Frequent reasons include unexplained fevers, chronic infections, fatigue, or symptoms like swollen lymph nodes. It may also be used to check for conditions like leukemia, lymphoma, or immune deficiencies.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

WBC Differential Profile

Frequently asked questions

How might my results affect my care?
Abnormal counts can signal infections (e.g., high neutrophils), immune disorders (e.g., low lymphocytes), or other systemic issues. For example, a high eosinophil count might suggest allergies or parasitic infections, while a low monocyte count could indicate chronic inflammation.
What do my specific cell counts mean?
Your doctor will interpret your results alongside your symptoms and medical history. For instance, a shift in neutrophil-to-lymphocyte ratios could indicate a bacterial infection, while a high eosinophil count might point to an allergic reaction or parasitic disease.
Can I prepare for this test?
No special preparation is needed, but avoid heavy meals or strenuous activity before your blood draw. If you’re on certain medications (like steroids), let your healthcare provider know.
  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