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Test Code 0560 ADAMTS13 Evaluation

Performing Laboratory

Blood Center of Wisconsin

Methodology

Reflex Tests

 

Test ID Reporting Name Available Separately
F13AB ADAMTS13 Antibody  No
FAINH ADAMTS13 Inhibitor No

Testing Algorithm:

If ADAMTS13 Activity is ≤30%, then ADAMTS13 Inhibitor will be performed, when appropriate, at an additional charge.

If ADAMTS13 Inhibitor is ≥0.7 inhibitor units, then ADAMTS13 Antibody will be performed, when appropriate, at an additional charge.

Method Name:

Fluorescent Resonance Energy Transfer (FRET)

 

Specimen Requirements

Draw blood in a light-blue top (sodium citrate) tube. Spin down and send 1 mL of citrated plasma frozen in plastic vial.

Note: Patient’s date of birth is required.

 

Reject Due To:

Hemolysis: Mild OK; Gross reject

Thawing: Warm reject; Cold reject

Lipemia: NA

Icterus: NA

Other: NA

Day(s) Test Set Up

Monday through Friday

Reference Values

ADAMTS13 Activity Reference Interval: ≥67%

 

Interpretive Comments: ADAMTS13 activity is measured using FRETS-VWF73 substrate. Severe deficiency of ADAMTS13 (activity <5-10%) may be acquired or congenital, and is a relatively specific finding in patients with a clinical diagnosis of thrombotic thrombocytopenic purpura (TTP). Severe ADAMTS13 deficiency is observed in approximately two-thirds of patients with a clinical diagnosis of acute idiopathic TTP. In this patient population, persistence of severe ADAMTS13 deficiency during clinical 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 in children or adults as episodes of TTP. Severe ADAMTS13 deficiency persists during remission in these patients and auto-ADAMTS13 anti-body is generally not observed. Mild to moderate deficiency of ADAMTS13 activity has been observed in multiple medical conditions. Hyperbilirubinemia interferes with FRET-based assay of ADAMTS13 activity and plasma free hemoglobin >2 gm/L is a potent inhibitor of ADAMTS13 function.

 

ADAMTS13 Inhibitor Reference Interval: ≤0.4 Inhibitor Units

 

Interpretive Comments: Inhibitor activity is determined using mixing studies with normal pooled plasma and residual ADAMTS13 activity is measured using FRETS-VWF73 substrate. In patients with acute idiopathic thrombotic thrombo-cytopenic purpura (TTP), severe ADAMTS13 deficiency is attributed to circulating auto-ADAMTS13 antibody. Publications suggest that inhibitory antibody is observed in 44-93% of such patients. Persistence of inhibitory auto-antibody during symptomatic remission of TTP suggests an increased risk for subsequent clinical relapse. Auto-antibody is not implicated in the mechanism of congenital ADAMTS13 deficiency (Upshaw-Schulman syndrome). Severe hemolysis (plasma free hemoglobin >2 gm/L) and hyperbilirubinemia (total bilirubin >15 mg/dL) can cause an artifactually positive ADAMTS13 inhibitor result. Correlation with clinical data and the ADAMTS13 activity result is suggested.

 

ADAMTS13 Antibody Reference Interval: ≤18 Arbitrary Units

 

Interpretive Comments: IgG antibody to ADAMTS13 is detected by ELISA assay. Results less than or equal to 18 are interpreted as negative, 19-27 are indeterminate, while levels greater than or equal to 28 are interpreted as positive. This serologic assay is less specific than the functional inhibitor assay, and positive results have been observed in some individuals without ADAMTS13 deficiency, including healthy individuals and patients with other immunologic disorders. In patients with acute idiopathic thrombotic thrombocytopenic purpura (TTP), severe ADAMTS13 deficiency is attributed to circulating auto-ADAMTS13 antibody. The magnitude of antibody concentration as measured by inhibitor titer correlates poorly with the level as measured by ELISA method. In some patients, the inhibitor assay is negative and only a serologic assay will detect the autoantibody. Persistence of autoantibody during symptomatic remission of TTP suggests an increased risk for subsequent clinical relapse. Autoantibody is not implicated in the mechanism of congenital ADAMTS13 deficiency (Upshaw-Schulman syndrome). Correlation with clinical data, ADAMTS13 activity and ADAMTS13 inhibitor results is suggested.

 

Test Classification and CPT Coding

85397-Coagulation and fibrinolysis, functional activity, not otherwise specified

85335-Factor inhibitor test (if appropriate)

83520-Antibody  (if appropriate)

Specimen Transport Temperature

Frozen

Barnes-Jewish Hospital Additional Information:

For BJH Laboratory Use Only

Laboratory Processing Instructions:

BJH Chemistry will forward to the performing laboratory.