Thrombotic microangiopathy after renal transplantation in the United States

Background: Analysis of the incidence, time to event, and risk factors for thrombotic microangiopathy (TMA) after renal transplantation (RT), has not been reported in a national population. Methods: This is a historical cohort study of 15,870 RT recipients in the United States Renal Data System (USRDS) with Medicare as their primary payer between January 1, 1998, and July 31, 2000, followed until December 31, 2000. Patients with Medicare claims with a diagnosis of TMA (International Classification of Diseases, 9th Revision, codes 283.11x or 446.6x) after RT were assessed by Cox regression. Results: Among patients with end-stage renal disease owing to hemolytic uremic syndrome (HUS), 29.2% later had TMA versus 0.8% of patients with ESRD owing to other causes. The incidence of TMA in RT recipients was 5.6 episodes per 1,000 person-years (PY; 189/1,000 PY; for recurrent TMA versus 4.9/1,000 PY for de novo TMA). The risk of TMA was highest for the first 3 months after transplant. Risk factors for de novo TMA included younger recipient age, older donor age, female recipient, and initial use of sirolimus. Patient survival rate after TMA was approximately 50% at 3 years. Conclusion: De novo TMA is uncommon and may occur later after RT than previously reported. Risk factors for de novo TMA were also identified.