Cattle-FRETS71, a novel fluorogenic substrate with broad applicability for characterizing ADAMTS13 properties and function.

BACKGROUND

Current ADAMTS13 activity assays are important for diagnosing thrombotic thrombocytopenic purpura (TTP) but are unreliable to assay ADAMTS13 activity in animal models. The Cattle-FRETS71 assay is capable of detecting ADAMTS13 activity in plasma from multiple animal species, making it a potentially useful reagent at all stages of clinical research. The performance of Cattle-FRETS71 in TTP diagnosis is not yet known.

OBJECTIVES

We evaluated the performance of the Cattle-FRETS71 substrate against the human FRETS-rVWF71 and the FRETS-VWF73 commercial substrates in human plasma and serum samples to validate its utility in diagnosing TTP in patients.

METHODS

Internal validation was performed using heparinized plasma samples (n = 81). External validation was a blinded study using serum samples from the Oklahoma TTP Registry (n = 118, collected 2004-2014) that had been initially assayed by FRETS-VWF73 within 1 year of collection. Additional validation was performed with citrated plasma samples with variable ADAMTS13 activities (n = 32) that were analyzed by FRETS-VWF73.

RESULTS

There was an excellent correlation (r = 0.94) between Cattle-FRETS71 and FRETS-rVWF71 for assayed heparinized plasma samples (n = 81). Assay results between Cattle-FRETS71 and FRETS-VWF73 of Oklahoma TTP Registry serum samples (n = 118) and citrated plasma samples (n = 32) were comparably good (r = 0.81 and r = 0.85, respectively).

CONCLUSION

The Cattle-FRETS71 assay is comparable with other assays in quantifying ADAMTS13 activity in human plasma collected from patients with documented or suspected TTP. The versatility of Cattle-FRETS71, combined with its specificity and sensitivity, makes it a useful tool for the standardization of ADAMTS13 activity across basic and clinical research paradigms.