4
Diagnosis
Table 2. Diagnosis in settings with timely access to
plasma ADAMTS13 testing and for patients with
INTERMEDIATE or LOW clinical suspicion of iTTP
Step 1. Acquire a plasma sample for ADAMTS13 testing (e.g., ADAMTS13 activity
and inhibitor or anti-ADAMTS13 IgG) before an initiation of TPE or use
of any blood product.
Step 2. Consider starting TPE and corticosteroids, depending on the clinician's
judgement and assessment of the individual patient.
Step 3. Do not start caplacizumab until the result of plasma ADAMTS13 activity is
available.
Step 4. When the result of plasma ADAMTS13 activity testing is available, consider
adding caplacizumab and rituximab (see Recommendation 2 in Management
Guidelines) if ADAMTS13 activity is less than 10 IU/dL (or less than 10%
of normal) with an inhibitor or elevated anti-ADAMTS13 IgG (a positive
test result), but do not start caplacizumab and consider other diagnoses
if ADAMTS13 activity is greater than 20 IU/dL (or ≥20% of normal) (a
negative result).
Note: Clinical judgement is required for continuing or stopping TPE and corticosteroids, or
adding caplacizumab or rituximab when plasma ADAMTS13 activity is between 10 and
20 IU/dL.
➤ In settings with timely access to plasma ADAMTS13 testing and for
patients with intermediate or low clinical suspicion of iTTP (e.g., based
on clinical assessment or a formal clinical risk assessment method),
the panel suggests the following diagnostic strategies (See Table 2).
(C-L)
