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von Willebrand Factor Cleaving Protease
|Approval req'd?||Yes, for any stat requests contact either Dr. Scott Kogan or Dr. Andrew Leavitt for approval.|
|Test group||von Willebrand|
|Performed by||Machaon Diagnostics|
|Collection Instructions||1. Check the expiration date on the label of the blue top vacutainer before drawing the patient.
2. For blood collection in a sodium citrate blue top, the tube must be filled to above the Minimum Fill Indicator on the tube. It is crucial to wait and allow the tube to stop filling before removing it from the needle.
3. With use of a butterfly needle, draw about 1 cc using a separate blue top to remove air from tubing, discard the first tube and then draw a second blue top tube filled to the full extent of the vacuum.
4. Tubes should not be filled past the Maximum Fill dashed line by either using a syringe or removing the tube cap.
|Container type||Blue top filled to full extent of vacuum|
|Amount to Collect||2.7 mL blood|
|Sample type||Citrated platelet poor plasma|
|Preferred volume||1 mL plasma|
|Min. Volume||1 mL plasma|
|UCSF Rejection Criteria||Samples collected in outdated blue top vacutainer. Over-filled or under-filled tubes may be rejected Marked hemolysis or hyperbilirubinemia|
|Processing notes||Aliquot plasma and maintain at ambient. Call Machaon courier at (510) 839-5600. After hours and weekend samples will be handled by Hematology.|
|Ref Lab Rejection Criteria||Marked hemolysis or hyperbilirubinemia|
|Critical value||Machaon: < 10%|
|Stability||Room temperature 7 days|
|Turn around times||1 - 2 days|
|Reflex?||Yes, If the test for Protease Inhibitor is required, it will be ordered and billed at an additional charge.|
|Additional information||A severe decrease in ADAMTS-13 activity to less than 10% has been shown to be diagnostic for Thrombotic Thrombocytopenic Purpura (TTP), an illness characterized by thrombocytopenia, microangiopathic hemolytic anemia (MAHA), fever, renal dysfunction and central nervous system ischemia. TTP is often difficult to diagnose as well as differentiate from other thrombotic microangiopathies (TMA) such as hemolytic uremic syndrome (HUS) and atypical hemolytic uremic syndrome (aHUS).
TTP is characterized by the acquired or congenital deficiency of ADAMTS-13 activity. An antibody inhibitor will be present in roughly half of the cases diagnosed with idiopathic TTP.
Early diagnosis is paramount. Left untreated, TTP has a mortality rate above 90%; however, rapid diagnosis and treatment with plasma exchange improve the mortality rate to below 20%.
To maximize the clinical utility of this test, Machaon Diagnostics is offering ADAMTS-13 activity and inhibitor testing on a daily basis with clinical consultation.
Inhibitor assay is performed as a reflex if levels are low.
Absent or low levels of ADAMTS13 activity may allow the accumulation of ultra-large von Willebrand factor multimers (ULVWF) in plasma. It is hypothesized that these ULVWF cause the intravascular platelet aggregation characteristic of TTP.
Activity levels below 10% are seen in acute and relapsing idiopathic (autoimmune) thrombotic thrombocytopenic purpura (TTP) but also in a rare hereditary gene mutation of VWF protein at the cleavage site. Activity levels between 10 and 30% may be seen in some instances, including when immunosuppressive therapy or recent plasmapheresis exchange has been started. Mild decreases in ADAMTS-13 activity are seen in a wide variety of conditions including metastatic cancer, neonates, serious infections and cirrhosis of the liver.
|CPT coding||85247-90 (activity), 85335-90 (inhibitor)|
|Last Updated||2/18/2015 11:16:49 AM|