The utility of patient characteristics in predicting severe ADAMTS13 deficiency and response to plasma exchange.
BACKGROUND
Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare form of thrombotic microangiopathy (TMA) characterized by extreme deficiency of ADAMTS13, an enzyme responsible for cleavage of von Willebrand factor. Plasma exchange therapy is the cornerstone of current treatment and is ineffective for most other forms of TMA. The availability of ADAMTS13 testing has improved diagnostic accuracy and appropriate selection of patients who are most likely to respond to plasma exchange.


METHODS
We performed a retrospective chart review of 110 cases of clinically suspected TTP with ADAMTS13 test results from 2005 to the present. The primary goal was to identify presenting clinical and/or laboratory features of patients with ADAMTS13 deficiency that would prove useful in increasing the likelihood of, or excluding the possibility of, TTP. In addition, patient outcomes including alternative diagnoses and response to plasma exchange were reviewed.


RESULTS
Significant correlations for severe ADAMTS13 deficiency were seen for four of the observed variables: indirect bilirubin, reticulocyte percentage, creatinine, and platelet count; a fifth variable, D-dimer, just missed significance but performed well in subsequent analysis. Receiver operator characteristics curves for individual variables had area under the curve (AUC) values ranging from 0.75 to 0.85; a combined model had an AUC of 0.98. In addition, we constructed tree models both for clinical use as a diagnostic algorithm and for recursive partitioning to help establish cutoff points for categorical variables in developing an easy-to-use clinical prediction score.


CONCLUSIONS
These results may enable the rapid exclusion and accurate diagnosis of TTP using readily available laboratory data.
Bentley
Melissa J
MJ
Department of Internal Medicine, University of Utah Health Sciences Center, and ARUP Laboratories, Salt Lake City, Utah, USA. melissa.bentley@hsc.utah.edu
Lehman
Chris M
CM
Blaylock
Robert C
RC
Wilson
Andrew R
AR
Rodgers
George M
GM
D051722:ADAM Proteins / Q000097:blood / Q000172:deficiency*; D000071120:ADAMTS13 Protein; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D010951:Plasma Exchange; D010976:Platelet Count; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D012189:Retrospective Studies
D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human