In 1,814 patients with sickle cell disease who had been transfused, the overall rate of alloimmunization to erythrocyte antigens was 18.6%. The rate of alloimmunization in this group appears to be an explicit function of the number of transfusions received because it increases exponentially with increasing numbers of transfusions. Alloimmunization usually occurred with less than 15 transfusions, although the rate of alloimmunization continued to increase when more transfusions were given. The rate of alloimmunization was less in patients with hemoglobin SC disease and sickle-beta+ thalassemia because these patients had received fewer transfusions. Children less than 10 years old had a slightly lower rate of alloimmunization than patients in other age groups even after correction for the number of transfusions given. Women were more frequently alloimmunized than men; this was largely due to the fact that women received more transfusions than men, but in the age group 16 to 20 years the increase may have been due in part to alloimmunization owing to pregnancy. Forty-five percent of those alloimmunized made antibodies of only one specificity; 17% made four or more antibodies reacting with different antigens. Antibodies to the C and E antigens of the Rh group, the Kell antigen, and the Lewis antigens were most commonly made. These findings may be important in formulating a rational transfusion policy in sickle cell disease.

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Although abnormalities in coagulation tests have been reported during vaso-occlusive crises in patients with sickle cell disease, objective, readily performed laboratory tests that document the occurrence of this complication have not been available. We examined the relationship between fibrin D-dimer levels and the occurrence of complications in patients with sickle cell disease, using a commercially available latex bead agglutination assay. The patients were either asymptomatic, hospitalized for vaso-occlusive crisis, or had other complications of sickle cell disease including leg ulcers, chronic cholecystitis, aseptic necrosis, joint pain and infection. Fifty-seven percent of 187 samples on 96 patients had elevated levels of fibrin D-dimer. Ninety percent of 75 samples from asymptomatic patients were negative for fibrin D-dimer (less than 1 microgram/ml) but 97% of 29 samples from patients with vaso-occlusive crisis and 85% of 83 samples from patients with other complications of sickle cell disease were positive. In serial studies, worsening or amelioration in clinical complications were reflected in increasing or decreasing levels of fibrin D-dimer, respectively. The molecular species of fibrin identified by the latex agglutination test was shown to be fragment D-dimer by successive immunoprecipitation and protein blot analysis. We conclude that the complications of sickle cell disease, including vaso-occlusive crisis, result in the production of fibrin D-dimer, and its detection may be used as a marker for the presence of the complication.

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There is wide variation in the clinical manifestations of sickle cell disease (SCD) from one affected individual to another. Many investigators have sought to discern parameters that would explain this variability. In the present studies we have attempted to correlate the frequency of painful events and the extent of end organ failure in SCD with rheologic properties of packed suspensions of sickle cells, using a magneto-acoustic ball microrheometer developed in our laboratory. Using this device we have measured the steady-state viscosity, and the viscous and elastic moduli of cell suspensions in 16 individuals with hemoglobin SS disease who were untransfused and in their steady state. The rheologic parameters were then correlated with clinical parameters. The clinical parameters measured were emergency department visits, hospitalizations, hemoglobin, reticulocyte count, age, and end organ failure (nephropathy, avascular necrosis of bone, stroke, retinopathy, resting hypoxemia after acute chest syndrome(s), leg ulcer, and priapism with impotence). The P value for the correlation between the steady state viscosity and end organ failure was .001 with a correlation coefficient (R value) of .73. The P value for the correlation between the viscous modulus of viscosity and end organ failure was .00006 with an R value of .83. The P value for the correlation between the elastic modulus of viscosity and end organ failure was .0006 with an R value of .76. However, there was no significant correlation between any component of packed cell rheology and emergency department visits or hospitalizations for pain.