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Immature Granulocytes

Historically, measurement of immature myeloid cells such as bands has been considered clinically useful for diagnosis of infection, especially for neonatal sepsis. However, most hospitals have stopped performing manual banc counts because they were proven to be inaccurate and imprecise. Perhaps the greatest problem with the band count is the inability to reproducibly identify band neutrophils. The literature contains at least three different definitions of a band neutrophil, leading to unacceptably wide interobserver variability. For example, the 95% confidence limit for 5% bands is 1% to 12%, for 10% bands the limit is 4% to 18%, and for 15% bands the limit is 8% to 24%.

Other immature granulocytes (IGs) including metamyelocytes, myelocytes, and promyelocytes have better morphological definition and together can be used as an alternative to the band count. IGs are usually not detected in healthy individuals but are elevated in patients with bacterial infections, acute inflammatory disorders, cancer (marrow metastasis), tissue necrosis, acute transplant rejection, surgical and orthopedic trauma, myeloproliferative neoplasm, steroid use, and pregnancy. Usually an increase in IGs is accompanied by an increase in the absolute neutrophil count. However, elderly patients, neonates, and patients with myelosuppression may have elevated IGs without an elevation of the neutrophil count.

Sysmex XN hematology analyzers perform the IG count as a part of the leukocyte differential count with notably low imprecision (CV near 7%). In addition, the accuracy of these measurements compared to microscopic examination or flow cytometry with monoclonal antibodies has been shown to be high (correlation coefficient of 0.78-0.96).

Validation studies performed in our own laboratory confirmed that healthy individuals (n=28) have an average IG count of 0.36% (range 0.2% to 0.5%), while inpatients (n=96) have an average IG count of 2.1% (range 2.0% to 6.2%). An increase in IGs of >2% can be a useful in identification of acute infection. Published studies have shown high specificity of IG count for infectious diseases but low sensitivity, precluding the use of such a count as a screening test for sepsis.

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