What Are Immature Granulocytes (IG#)

What are immature granulocytes (IG#)

Immature granulocytes (IG) are early forms of white blood cells that normally mature in the bone marrow and enter the blood only when fully mature. When the body faces a strong infection, inflammatory process, or other stress, the bone marrow begins producing granulocytes faster and releases some into the blood earlier than usual. IG# shows the absolute count of these immature cells.

This marker is determined by modern automated haematology analysers and is reported in thousands of cells per microlitre (10³/µL).

Reference ranges

The absolute count of immature granulocytes in adults is typically up to 0.06 × 10³/µL. In healthy adults, there are usually very few or no immature granulocytes in the blood. A value above the reference range signals that the bone marrow is working more intensively than usual.

Why immature granulocytes may be elevated

An elevated IG# most commonly indicates that the body is responding to an acute infection — especially bacterial. It is one of the earliest signs of infection in the blood, sometimes detectable before CRP or white blood cell count increases. Sepsis (severe systemic inflammation due to infection) is often accompanied by a significant increase in immature granulocytes.

Other possible causes: acute inflammation (e.g., appendicitis, pancreatitis), surgical intervention, severe physical stress, tissue damage (burns, trauma). Myeloproliferative diseases and other haematological conditions can also lead to elevated IG#.

During pregnancy, the immature granulocyte count may physiologically increase, especially in the third trimester.

Why immature granulocytes may be low

Since the normal IG# is close to zero, a decrease is practically not evaluated. An undetectable or very low immature granulocyte count is normal and indicates that the bone marrow is functioning calmly.

What to do with your result

If IG# is elevated, the doctor will evaluate it together with other markers — total white blood cells, neutrophils, CRP, procalcitonin — and clinical symptoms (fever, pain, weakness). An elevated IG# can prompt faster diagnosis because it signals infection early.

If you feel well and IG# is only slightly above normal, the doctor may recommend repeating the test in a few days. After an infection or surgery, the marker usually normalises on its own.

Monitoring over time

IG# is most valuable as an acute process marker — it responds quickly and normalises quickly. Long-term monitoring is relevant only for haematological conditions. If your test showed an elevated IG# and the doctor prescribed treatment, a repeat test shows whether the body is responding to treatment.

Questions for your doctor

1. Could an elevated IG# indicate an active infection, even if I feel reasonably well? 2. Are additional tests needed (CRP, procalcitonin, blood culture)? 3. Do my other white blood cell differential results confirm signs of inflammation or infection? 4. When should the test be repeated to check whether the marker has normalised?

*This is not medical advice. Consult your doctor regarding any health decisions.*