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Unit Code 91611:
ADAMTS13 Activity and Inhibitor

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Reference Values

ADAMTS13 Activity:  >=67%

ADAMTS13 Inhibitor:  <=0.4 Inhibitor Units

 

METHOD:  ADAMTS13 activity is directly measured by a

Fluorescence Resonance Energy Transfer (FRET) assay

(Kokame K, et al. Br J Haematol. 2005;129:93-100).

Inhibitor activity is determined using mixing studies;

one inhibitor unit is defined as the concentration

of inhibitor able to reduce the ADAMTS13 activity of equal

volume of normal pooled plasma by half (Zheng XL, et al.

Blood. 2004;103:4043-4049).

INTERPRETIVE COMMENTS:  Severe deficiencies of ADAMTS13

(activity <5-10%) appear to be a relatively specific

finding in patients with a clinical diagnosis of idiopathic

thrombotic thrombocytopenic purpura (TTP). At presentation,

most (but not all) patients with idiopathic TTP will show

severe ADAMTS13 deficiency, and a functional inhibitor

can be demonstrated in 40-90% of these individuals. Plasma

exchange therapy may induce remission of clinical symptoms

of TTP despite persistence of severe ADAMTS13 deficiency.

A persistently abnormal ADAMTS13 assay during remission is

associated with an increased risk for recurrent clinical

episodes of TTP. Severe congenital ADAMTS13 deficiency

(Upshaw Schulman syndrome) is an autosomal recessive

condition which may present as thrombotic microangiopathy

in either children or adults; inhibitors are generally not

observed in these patients. Other conditions where severe

ADAMTS13 deficiency has been reported include disseminated

intravascular coagulation, metastatic malignancy, advanced

cirrhosis and severe sepsis. Severe ADAMTS13 deficiency is

rarely observed in secondary thrombotic microangiopathies

(e.g. diarrhea-associated hemolytic uremic syndrome or

after hematopoietic stem cell transplantation). Mild to

moderate deficiency of ADAMTS13 activity has been observed

in multiple medical conditions. Hemolysis with plasma free

hemoglobin greater than 2 gm/L or an elevated bilirubin level in

the sample can cause artifactually low ADAMTS13 activity and

false positive inhibitor results.

Effective 7/18/2008

 

  

Test Performed By:  BloodCenter of Wisconsin

                                         638 North 18th Street

                                         Milwaukee, WI  53233

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