Visualizing the marrow granulocyte reserve.

The MGR, the pool of band and segmented neutrophils from which sudden demands for extra blood neutrophils are met, has been studied by measuring blood neutrophil increments following administration of endotoxin, corticosteroids, or etiocholanolone. Alternatively its size may be estimated from marrow differential counts with or without estimates of marrow mass. In 34 studies of 31 patients with diverse causes of neutropenia, measurements were made of the MGR comparing endotoxin response and differential counts of marrow aspirates coupled with estimates of absolute marrow mass derived from EIT rate. Responses to endotoxin were normal in 10 studies and subnormal in 24. The factor which best predicted endotoxin response was the percent of marrow neutrophils and neutrophil precursors which were band and segmented forms. All responders to endotoxin had greater than 25% marrow neutrophils and neutrophil precursors that were band and segmented; 20 to 21 subjects with less than a normal response to endotoxin had less than 25%. These studies suggest that no further information is gained by measuring endotoxin response in neutropenic patients who have a reduced percent of band forms and segmented neutrophils in marrow aspirates.