What does a high immature granulocyte (IG) automated lab value indicate?

Understanding Elevated Immature Granulocyte Count in Laboratory Results

An elevated immature granulocyte (IG) count in laboratory testing primarily indicates an active bone marrow response to infection, particularly bacterial infection, and serves as a potential early marker for bacteremia and sepsis. 1, 2

What Are Immature Granulocytes?

• Immature granulocytes are early (immature) forms of neutrophils that are normally found in the bone marrow but appear in peripheral blood when there is increased demand for neutrophils, typically in response to infection 3
• These cells include metamyelocytes, myelocytes, and promyelocytes - precursors to fully mature neutrophils 1
• Their presence in peripheral blood reflects active bone marrow response, often to bacterial infection 2

Clinical Significance of Elevated IG Count

Infection and Sepsis

• Elevated IG percentage and count are significantly higher in infected patients compared to non-infected patients 1
• IG measurements can discriminate between systemic inflammatory response syndrome (SIRS) and sepsis with a sensitivity of 89.2% and specificity of 76.4%, particularly within the first 48 hours after SIRS onset 3
• The IG count increases with increasing invasiveness and severity of infection 4

Diagnostic Value

• An IG percentage >3% is considered a very specific predictor of sepsis and might help expedite microbiological evaluation 1
• IG count of >0.03 × 10³/mm³ and IG percentage >0.5% offer sensitivity of 86.3% and 92.2% respectively for detecting bacteremia 5
• Higher values (IG count >0.3 × 10³/mm³ and IG percentage >3%) have specificity greater than 90% for bacteremia, though these values are less frequently encountered 5

Comparison with Other Markers

• IG percentage has been shown to be a better predictor of infection than total white blood cell (WBC) count and comparable to absolute neutrophil count (ANC) 1
• In some studies, IG measurements demonstrated superior discriminative power for infection compared to C-reactive protein (CRP), lipopolysaccharide binding protein (LBP), and interleukin-6 (IL-6) within the first 48 hours 3

Specific Clinical Contexts

Infectious Diseases

• In tickborne rickettsial diseases like anaplasmosis, increased numbers of immature neutrophils are a characteristic laboratory finding 6
• Elevated IGs may be seen in various bacterial infections before positive blood cultures are obtained 4

Hematologic Disorders

• In hypocellular myelodysplastic syndromes and acute myeloid leukemia, immature granulocyte counts may be altered, though this represents a different pathophysiological process than infection-related elevation 6

Appendicitis

• In elderly patients with acute appendicitis, the delta neutrophil index (which measures the fraction of immature granulocytes) can independently predict the presence of perforation 6

Limitations

• Despite its utility, automated IG measurement is not sensitive enough to be used alone as a screening assay for prediction of infection or bacteremia 1
• The IG count is not suitable as a prognostic marker for mortality in critically ill patients 3

Clinical Application

• Routine and serial measurement of IGs may provide new possibilities for rapid screening of patients with suspected infections 3
• IG count adds value to WBC and CRP in the early exclusion of infection and can be obtained routinely without extra blood sampling or costs 4
• The automated measurement of IGs offers more reproducible, precise, and accurate counting compared to manual band counts, which have been notoriously difficult to measure accurately 5