Immature Granulocyte (Ig) Count (Blood)

Diagnostic Use

The Immature Granulocyte (IG) count in blood is a diagnostic marker used to detect early immune system activation. Immature granulocytes, (promyelocytes, myelocytes, and metamyelocytes) are normally present only in the bone marrow. Their appearance in peripheral blood suggests bone marrow stimulation, often due to infection, inflammation, or haematologic disorders. Elevated IG levels can serve as an early indicator of bacterial infections, sepsis, or systemic inflammation, sometimes preceding changes in total white blood cell count. Automated hematology analyzers now routinely measure IGs, aiding in rapid clinical decision-making, especially in critical care settings. However, the IG count should be interpreted alongside other clinical and laboratory findings, as it is not disease-specific. The IG count is reported as part of a 6-part WBC differential.

Interpretation

Measurement

Immature Granulocytes (promyeloctes, myelocytes and metamyelocytes) are usually classified on the basis of cell morphology by microscopical examination of a stained blood film. However the manual differential count is imprecise because of the small number of cells counted and interobserver variability. A Sysmex automated FBC analyser uses flow cytometry to classify thousands of white cells based on light scatter and fluorescent staining giving rise to discrete clusters corresponding to the cell types that are present. Immature Granulocytes have higher fluorescence than neutrophils and can be clearly separated. The IG count is reported as part of a six part WBC differential.

Causes of a raised IG count

The presence of IG may indicate sepsis, bacterial infection, inflammatory states, steroid therapy, malignancy, trauma or myeloproliferative diseases. They are also present in the later stages of pregnancy and in newborn infants.

Reference Intervals