Preliminary Results from the Surveillance, Epidemiology & Risk Factors for TTP (SERF-TTP) Group: A Prospective Case-Control Study of Idiopathic TTP.

SERF-TTP is the first prospective case-control study to investigate epidemiology, risk factors & outcomes in patients with first episode of idiopathic TTP. METHODS: Each case of TTP is identified upon referral for therapeutic plasma exchange (TPE). Exclusion criteria include organ or allogeneic stem cell transplant, anti-neoplastic therapy or malignancy. 2 age & gender-matched controls are identified for each case. Epidemiologic information, lab data & plasma samples are collected from each case. Case & control data are collected by standardized interview. Relative risk & 95% CI computed by chi-squared tests. ADAMTS13 activity & inhibitor are centrally measured on pre-TPE samples. ADAMTS13 activity is measured by FRETS-vWF73 assay (Peptides Int.). ADAMTS13 inhibitor is assessed by Technozym ADAMTS13 INH ELISA (Technoclone). RESULTS: Data is available for 67 cases & 138 controls. The median age of cases is 40, & 82% are female. Medical history & exposures are shown in Table 1. Clinical & lab characteristics vary by ADAMTS13 activity (Table 2). Low titer ADAMTS13 inhibitors are detectable in some patients with normal ADAMTS13 activity. 30 day survival of cases is 95.7%. Adverse reactions to TPE occur in 59% of patients, most commonly allergic(85%) or citrate-related reactions(65%). 14.7% had a venous access complication, 50% were catheter-related thromboses. 10% of all adverse events required an ICU admission. CONCLUSIONS: Preliminary results from the case-control study suggest that predisposing factors for the development of TTP include recent infection or connective tissue disorder. Cardiovascular disease, prior history of venous thrombosis, clopidogrel use and lower income are more common in TTP cases than controls. Patients with normal ADAMTS13 activity are more likely to present with higher platelet count, abnormal renal function and neurologic symptoms. Case & Control Characteristics Cases (n=67) Controls (n=138) Relative Risk (95% CI) Medical History Connective Tissue Disease 11.9% 2.2% 5.4 (1.5–20.0) Cardiovascular Disease 13.4% 3.6% 3.7 (1.29–10.6) Prior Venous Thrombosis 13.4% 2.9% 4.6 (1.48–14.5) Infection (prior 2 wks) 32.8% 10.1% 3.2 (1.77–5.9) Medications (prior 12 wks) Antibiotics 31.3% 17.4% 1.8 (1.08–2.99) Clopidogrel 4.5% 0.7% 6.4 (0.65–62.9) Income Level < $25,000 42% 18% 2.3 (1.47–3.6) $25,000 – 70,000 37.3% 52.9% 0.7 (0.49–0.99) > $70,000 11.9% 24.6% 0.5 (0.24–0.98) Characteristics by ADAMTS13 activity ADAMTS13 activity N ADAMTS13 inhibitor (>15 u/ml) ADAMTS13 inhibitor titer (mean) Platelets (mean) Creatinine (mean) Neurologic symptoms Survival Comparison of ADAMTS13 ≤20% vs > 20%, p-values: * 0.0028, † 0.003, ‡ 0.73, # 0.48. < 5% 18 (37.5%) 100% 80.9 22,350 1.4 44% 94% 5–20% 4 (8.3%) 100% 76.4 20,000 1.1 75% 100% > 20% 26 (54.2%) 57.7% 22.5 58,810* 4.3† 58%‡ 89.5%#