Immature Granulocytes (%) - Lab Results Explained

What are immature granulocytes?

Immature granulocytes (IGs) are developing white blood cells that are part of the body’s innate immune system, the fast-acting branch of immunity that responds quickly to infections and tissue injury. They are precursors to mature granulocytes (especially neutrophils), and typically include cells such as:

• Myelocytes

• Metamyelocytes

• (Sometimes promyelocytes, depending on the analyzer/reporting method)

Under normal conditions, these cells remain inside the bone marrow, where blood cells are produced and mature before being released into circulation.

What does Immature Granulocytes (%) measure?

IG% reports the proportion of immature granulocytes out of your total white blood cell count. It is commonly generated automatically by modern hematology analyzers as part of a CBC with differential.

Many labs also report:

• Immature Granulocytes (absolute) (IG#), which is the actual number of immature granulocytes per volume of blood

Both values can be helpful, because IG% can rise either due to:

• more immature cells being released, or

• changes in other white blood cell types that shift the percentage

Why this marker is clinically useful

Immature granulocytes are often considered a sign of increased bone marrow activity, meaning your body is rapidly producing and releasing infection-fighting cells. This can happen early in the course of illness and may appear before other classic findings, such as a significantly elevated total white blood cell count.

IG% is most useful as a supporting marker when clinicians are evaluating or monitoring:

• suspected bacterial infection

• systemic inflammation

• immune system stress (e.g., major illness, trauma, surgery)

• response to treatment over time

Typical reference range (and what counts as “high”)

Reference ranges vary slightly by lab and by age, but in many healthy adults, IG% is very low (often near zero).

A mild elevation can be transient and not always dangerous. However, higher values—especially when persistent or paired with symptoms—can be clinically meaningful.

In many clinical contexts, IG% above ~2–3% is considered more concerning and may raise suspicion for significant infection or systemic inflammation, particularly in acutely ill patients.

What does it mean if IG% is elevated?

An elevated Immature Granulocytes (%) result generally means your bone marrow is responding to a stressor by releasing immature white blood cells into the bloodstream. Common causes include:

Infection (especially bacterial)

One of the most common reasons for elevated IG% is infection, such as:

• pneumonia

• urinary tract infection

• skin and soft tissue infection

• bloodstream infection (bacteremia)

• sepsis (in more severe cases)

In some cases, IG% can rise early and help clinicians recognize infection sooner—especially when combined with symptoms, vital signs, and other lab markers.

Inflammation and immune activation

IG% may increase in inflammatory states, including:

• autoimmune disease flares

• severe inflammatory reactions

• inflammatory lung or systemic conditions

Physiologic stress and tissue injury

IG% can rise when the body is under strain, including:

• major surgery

• trauma or burns

• severe illness requiring hospitalization

• low oxygen states (hypoxia)

• acute cardiovascular stress in some settings

Bone marrow stimulation or recovery

Immature granulocytes can appear during periods of high bone marrow demand or rebound, such as:

• recovery after a serious infection

• recovery after chemotherapy or marrow suppression

• treatment with medications that stimulate blood cell production (in some cases)

Medications and hormonal states

Certain factors may increase IG% without a dangerous infection, including:

• corticosteroid therapy

• pregnancy (mild changes can occur)

Symptoms that may be associated with high IG%

IG% itself does not cause symptoms. Symptoms depend on the underlying cause. If IG% is elevated due to infection or inflammation, people may experience:

• fever or chills

• fatigue or weakness

• body aches

• cough or shortness of breath

• sore throat

• urinary pain or frequency

• abdominal pain

• rapid heart rate

• confusion (especially in severe infection)

If you have high IG% plus symptoms of serious infection, it should be evaluated promptly.

How clinicians interpret IG% in context

IG% is rarely interpreted alone. Providers typically look at it alongside:

• Total WBC count (high, normal, or low)

• Neutrophils (often elevated in bacterial infection)

• Bands / left shift (if reported separately)

• Lymphocytes (may change in viral illness or stress)

• CRP and/or procalcitonin (inflammation and infection markers)

• Clinical symptoms and vital signs (fever, blood pressure, heart rate, oxygen levels)

A high IG% may be especially concerning when paired with:

• high fever

• low blood pressure

• fast heart rate

• confusion

• worsening shortness of breath

• rising CRP or procalcitonin

• abnormal lactate (in suspected sepsis)

Can IG% be elevated without infection?

Yes. While infection is common, IG% can rise from non-infectious causes such as inflammation, stress, or medication effects. This is why IG% is best viewed as an early warning signal, not a standalone diagnosis.

Key takeaway

Immature Granulocytes (%) is an early marker of bone marrow activation and immune response. In healthy adults, it is usually very low. When elevated, it often suggests infection or inflammation, but it can also rise due to physiologic stress, medication effects, or bone marrow recovery. The result is most meaningful when interpreted with your symptoms, other CBC findings, and follow-up testing if needed.