Abstract
The hematologic hallmark of sickle cell disease is the irreversibly sickled cell (ISC) a shrunken, dehydrated cell which resists hypotonic lysis. Less well recognized in sickle cell disease is another population of cells geometrically “spherocytic” with decreased surface area to volume ratio and increased osmotic fragility. In 59 stable patients with HbSS, we determined hematologic values, ISC counts, the proportion of red cells identified by Nomarski optics as containing “pits”, and the proportion of osmotically labile cells. 80% of HbSS patients had an abnormal osmotic fragility curve characterized by a “tail” of hypotonically labile cells whereas none of the normal controls lysed in solutions less hypotonic than 0.5% saline. In patients with abnormal curves, 0.55% buffered saline hemolyzed 3.0 ± 2.7% of cells. HbSS patients with osmotically fragile cells had more ISC's (22 vs. 11%), lower Hgb's (7.7 vs. 8.5gm%), more reticulocytosis (20 vs. 15%) and lower Hb F values (7 vs. 12%) (p < 0.05 for all). Scanning electron microsopy of peripheral blood revealed ISC's and irregularly contoured spherocytic cells. In the group with abnormal fragility, the proportion of osmotically labile cells correlated inversely with Hgb, positively with reticulocyte count, positively with MCHC, and surgical splenectomy status (p < 0.05 for all); those with splenectomy had more spherocytic cells. This proportion did not correlate with “pit count”, age (after 2 years), the patient's sex, or MCV. These results indicate that in addition to ISC's, a second population of damaged erythrocytes characterized by increased osmotic lability circulate in patients with sickle cell disease and may be important in the pathogenesis of anemia.
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