From Bands to Grans
We’ve come a long way since the days of a patient arriving in the ED with belly pain and going to the OR based on an imprecise band count. Imprecision can be estimated mathematically as:
2 Standard Deviations = 2 x SQRT((# cells x (100 - # cells)) / total cells counted)
Thus, counting nine bands in a 100-cell differential has a theoretical range of 3 to 15 cells, but actual mileage varies dependent on the quality of the smear, quality of the stain, who counts the differential, how many abnormal cells have been seen that day, cultural shifts in what a “band” is, and naturally if the lab reports bands at all. Last year we stopped reporting bands. Finally.
The absolute neutrophil count (ANC) measured by modern instruments fills this void, along with toxic changes associated with an infectious process. These may include toxic granulation, Dohle bodies, and vacuolation. In recent years a new parameter has emerged that I’m excited about: the immature granulocyte count.
As stated in the American Journal of Clinical Pathology as early as 2003, “Receiver operating characteristic curves show that the percentage of immature granulocytes was a better predictor of infection than the WBC count and comparable to the ANC... a percentage of immature granulocytes of more than 3 was a very specific predictor of sepsis and might help expedite microbiologic laboratory evaluation of a subset of patients.”
Another study from 2012 using the same instrument (SE-2100) concludes: “Automated determinations of immature granulocytes and immature myeloid information seem to be useful adjunctive methods in the diagnosis of neonatal early onset sepsis.”
Most recently, the immature granulocyte count was found to discriminate between infected and non-infected patients (sensitivity / specificity = 89.2 / 76.4) within the first hours of SIRS (systemic inflammatory response syndrome, a broader term including sepsis). The study concludes: “Routine and serial measurement of IGs may provide new possibilities for rapid screening of SIRS patients on ICU with suspected infections.”
Any way you cut it, that beats the old 100-cell differential with a band count, especially on those busy Saturday nights when the ED is hopping.
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