ADAMTS-13 Levels Do Not Predict Outcome in Thrombotic Thrombocytopenic Purpura: Protein S Levels Are Maintained during Plasma Exchange with Solvent Detergent Treated Plasma.

Introduction The ultimate therapy for TTP is not yet defined. While approximately 85% of patients respond to plasma exchange with FFP, the use of alternative solutions such as cryosupernatant plasma, which is deficient in the high molecular weight forms of vWF. has not been proven by appropriate randomized prospective sample trials. However, it is intellectually appealing. Additionally, the use of the ADAMTS 13 level either to predict disease or outcome has not been resolved.

Methods Cryosupernatant plasma (CSP) was compared to solvent detergent treated plasma (SDP) over one cycle (nine days) of plasma exchange (PE) and subsequent procedures as required. Throughout treatment, ADAMTS 13 and protein S levels were followed.

Results At the primary end point of one month, 3 of 35 of the CSP and 1 of 27 of the SDP patients died. The average platelet count was 184 × 10⁹ per litre for CSP and 209 × 10⁹ per litre for SDP. While vWF and FVIII were elevated in all patients at entry, no unusually large vWF multimers were seen at any time. At entry 9 patients had ≤ 0–10% ADAMTS 13 and 14 of 62 had normal levels with the rest in between. At presentation only 9 patients had 100% inhibitor activity with no inhibitor in 18 patients. Of the four patients who died, two who received CSP, had 100% enzyme activity at presentation whereas one had no ADAMTS-13 and another had 10%. All 4 patients died within 10 days. Fifteen patients with less than 10% enzyme activity had >1.5 vWF. However, elevated (>3u/mL) vWF was seen in the presence of normal ADAMTS-13 levels. Six months after remission, and in the presence of a normal platelet count, ADAMTS13 remained low in 5 patients and normal in 15.Protein S levels in 41/62 patients studied showed little variation during therapy with values on day 3 and 5, similar to those seen on entry.

Conclusion In idiopathic TTP, ADAMTS 13 levels do not correlate with disease, and are not predictive of outcome. While protein S levels in the SDP were lower than those found in FFP, this did not appear to have clinical significance.