Platelet-Poor Plasma

1. Specimen must be drawn prior to replacement therapy.
2. Spin down, remove plasma, and spin plasma again.
3. Freeze specimens immediately at < or = -40 degrees C, if possible.
4. Send specimens in the same shipping container.

Additional Information:
1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
2. If priority specimen, mark request form, give reason, and request a call-back.
3. Each coagulation assay requested should have its own vial.

2 mL in TWO Light Blue top tubes, each containing 1 mL

5 days upon receipt at reference laboratory
ADAMTS13 Activity Assay: 24 hours
ADAMTS13 Inhibitor Assay: 3-5 days
ADAMTS13 Bethesda Titer: 3-5 days

ADAMTS13 ACTIVITY ASSAY
> or =70%

ADAMTS13 INHIBITOR SCREEN
Negative

ADAMTS13 BETHESDA TITER
<0.4 BU

Testing begins with ADAMTS13 activity assay to evaluate the percent activity. If the ADAMTS13 activity assay is <30%, an inhibitor screen will be performed to look for specific ADAMTS13 inhibition. If specific inhibition is apparent, the titer of the inhibitor will be determined.

Useful For:
Assisting with the diagnosis of congenital or acquired thrombotic thrombocytopenic purpura.

Cautions:
The ADAMTS13 activity assay is an in vitro assay using a synthetic substrate peptide in a static liquid environment. The measured ADAMTS13 activity may not reflect the true in vivo biological ADAMTS13 activity.

Not all patients with a clinical diagnosis of idiopathic thrombotic thrombocytopenic purpura (TTP) have a severe ADAMTS13 deficiency. Conversely, patients with other non-TTP conditions may have a severe ADAMTS13 deficiency (< or =10%). These conditions include hemolytic uremic syndrome, hematopoietic stem cell and solid organ transplantation, liver disease, disseminated intravascular coagulation, sepsis, pregnancy, and certain medication. Therefore, TTP remains a clinical diagnosis.

Interferences of ADAMTS13 activity assay include high levels of endogenous von Willebrand factor, hyperlipidemia, hemolysis with plasma free hemoglobin >2 g/L, hyperbilirubinemia (bilirubin concentration >100 micromolar), and cleavage by other protease.

Recent plasma exchange or transfusion may falsely normalize ADAMTS13 levels, thus potentially masking the diagnosis of TTP.

The impact of ADAMTS13 levels and presence of inhibitors on overall survival, ultimate clinical outcome, responsiveness to plasma exchange, and relapse are still controversial. Therefore, clinical correlation is recommended.

Please review the Coagulation Studies page for detailed instructions. Print, complete, and submit the Coagulation Patient Information Sheet from Mayo Medical Laboratories with the sample(s) and the A-1a Miscellaneous Request or Epic Req.

ADMFX: Fluorescence Resonance Energy Transfer (FRET)
ADMIS, ADMBU: Mixing Studies

85397-ADAMTS13 activity assay
85335-ADAMTS13 inhibitor screen assay (if appropriate)
85335-ADAMTS13 Bethesda titer (if appropriate)