The utility of ADAMTS13 in differentiating TTP from other acute thrombotic microangiopathies: Results from the UK TTP Registry

Abstract

Thrombotic microangiopathies (TMAs) are frequently difficult to differentiate clinically, and measurement of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) remains vital in thrombotic thrombocytopenic purpura (TTP) diagnosis. We retrospectively reviewed cases referred for ADAMTS13 testing, using UK TTP Registry screening data. Of a total 810 cases, 350 were confirmed as TTP. The 460 non-TTP cases comprised secondary TMAs (24·57%) and haemolytic uraemic syndrome (HUS) (27·17% aHUS, 2·83% Shiga-like toxin-producing E. coli [STEC]-HUS); the remainder were TMAs with no clear association, not TMAs, or had no confirmed diagnosis. ADAMTS13 levels were significantly lower in TTP than STEC-HUS, aHUS and other TMAs. TTP patients had significantly lower platelet count (15 × 109/l; range 0-96) than aHUS (57 × 109/l; range 13-145, P < 0·0001) or STEC-HUS (35 × 109/l; range 14-106, P < 0·0001); they also had lower creatinine levels (92 μmol/l; range 43-374) than aHUS (255 μmol/l; range 23-941, P < 0·0001) and STEC-HUS (324 μmol/l; range 117-639, P < 0·0001). However, 12/34 (35·3%) aHUS patients had a platelet count <30 × 109/l and 26/150 (17·3%) of TTP patients had a platelet count >30 × 109/l; 23/150 (15·3%) of TTP patients had a creatinine level >150 μmol/l. This study highlights the wide variety of TMA presentations, and confirms the utility of ADAMTS13 testing in TTP diagnosis.