6
Diagnosis
Figure 1. A suggested diagnostic and management strategy
for patients with HIGH pretest probability of
immune TTP
If ADAMTS13 activity will be
available within 72 hours
(scenario A) OR
If ADAMTS13 activity will be
available between 72 hours
and 7 days (scenario C)
Pretest probability of TTP should be determined based on clinical parameters (e.g. PLASMIC or
French score). If probability of TTP is high, start TPE and corticosteroids and collect plasma samples
for ADAMTS13 testing (e.g. activity and inhibitors or anti-ADAMTS13 IgG) before therapy.
Consider caplacizumab if ADAMTS13 test results are expected within 72 hours; if ADAMTS13 test
results are not available, do not start caplacizumab; if ADAMTS13 <10 IU/dL (or 10% of normal),
continue caplacizumab and rituximab. If ADAMTS13 is ≥20 IU/dL (or 20% of normal), consider
stop caplacizumab and seek other diagnoses. However, if ADAMTS13 activity is in borderline
(10–20 IU/dL or 10–20% of normal), clinical judgement is required for continuing therapy and
other alternative diagnostic approaches. (All are conditional recommendations in the setting of low
certainty of evidence). Here "treatment" includes caplacizumab and other therapies (such as TPE and
steroids.)
Start TPE + steroids
If ADAMTS13 activity will not be
available (scenario B)
Collect plasma for ADAMTS13
activity and inhibitors (or anti-
ADAMTS13 lgG)
Consider early caplacizumab
Stop caplacizumab
Consider other
diagnoses
NEGATIVE
Activity >20 U/dL
(or 20%)
BORDERLINE
Activity 10-20 U/dL
(or 10-20%)
Use clinical judgement to
guide treatment
Consider other
diagnoses
Continue caplacizumab
Consider adding
rituximab
Do not add caplacizumab
Consider rituximab
POSITIVE
Activity <10 U/dL
(or <10%)
Patient with HIGH (≥90%)
pretest probability of TTP
Evaluate pretest probability of TTP
Based on clinical judgement or a risk assessment model
