The staphylococcal protein A (SPA) column used to treat refractory autoimmune and alloimmune thrombocytopenia and rheumatoid arthritis patients is primed with heparin to prevent possible fibrin clot formation when the patient's plasma is passed through the column. A BMT patient with refractory alloimmune thrombocytopenia had prolonged activated partial thromboplastin times (aPTTs) at the end of SPA column treatments. This observation led to in vivo and in vitro analysis of the kinetics of heparin elution from the SPA column.
Two patients with refractory rheumatoid arthritis, who were treated on five occasions with the SPA column (as a part of a national trial) primed with 5000 U of heparin, were monitored for aPTT and heparin in their plasma. In addition, two in vitro analyses were performed with FFP for heparin elution from the SPA column.
The in vivo studies showed the presence of 0.3 to 1.5 U per mL of heparin in patients' plasma at the end of the SPA column treatments that corresponded with the prolonged aPTTs. The in vitro studies showed that 82 to 85 percent heparin (approx. 4400 U) was eluted from the SPA column during rather than before the procedure.
Patients undergoing SPA column treatments, especially those with thrombocytopenia, may be at increased risk of bleeding as a result of the presence of a significant amount of heparin in their circulation during the entire period of SPA column treatment.