Inferior Vena Cava Filters as a Potential Non-immune Cause of Low Serum Haptoglobin

Objective: Serum haptoglobin level is commonly used as a marker of hemolysis. We hypothesized that inferior vena cava (IVC) filters may be a potential non-immune etiology for subclinical hemolysis and low haptoglobin in some patients, after encountering a patient with an IVC filter, mild macrocytic anemia and unexplained severe haptoglobinemia. IVC filters can be associated with pressure gradients and turbulent blood flow in the presence of trapped clots and thrombus formation. Methods: Prospective study in patients undergoing IVC filter placement at our institution over a 3-month period in 2008. All patients had a haptoglobin level prior to filter placement, and then daily for a period of 3-14 days. The absolute and relative change in haptoglobin compared to pre-procedure levels was determined. Results were evaluated by t-test (paired, 2-tail). Statistics and graphics were performed with commercial software. Results: A total of 22 patients underwent IVC filter placement. Four patients were excluded due to low preprocedure haptoglobin levels. At least one post-procedure haptoglobin values was available until day 3 in 18/18 eligible patients. Nine patients were followed for a period of 1-2 weeks. Although the majority of patients had an increase in haptoglobin after IVC filter placement, 3/9 (30%) had >50% decrease in haptoglobin by day 7, including one patient with severe haptoglobinemia by day 14. Patients with decreased haptoglobin levels also had decreases in platelet count over the same period. Conclusion: These results suggest that IVC filters may be another non-immune, device-related cause of decreased haptoglobin in some patients.