Spur cells manifested a striking increase in cholesterol content and in the cholesterol: phospholipid ratio, but a normal osmotic fragility. When incubated in heated normal serum, spur cells lost their excess cholesterol and became spherocytic and osmotically fragile. Conversely, sera from patients with spur cells readily transferred up to one-third of their free cholesterol to normal red cells, causing normal cells to become resistant to osmotic lysis. In addition, these sera caused normal red cells to acquire thorny membrane projections. Cholesterol transfer to normal cells also occurred from normal serum which had previously been incubated with spur cells. Changes in cell cholesterol were induced by all of the lipoprotein fractions of spur serum.

When transfused into a patient with spur cells, normal red cells became more resistant to osmotic lysis over the course of 24 hr. However, over the subsequent 7 days they underwent a progressive increase in osmotic fragility. These normal cells, as well as the patient's own cells, had a shortened survival. Correlating with the moderate decrease in the filterability of red cells spurred in vitro, red cell destruction occurred predominently in the spleen.