Enzyme Activity and Inhibitor Screening Services
ADAMTS13 Enzyme Activity Assay
Measure VWF-cleaving protease activity in citrated plasma with a FRET-based assay designed to support the diagnosis and monitoring.
What This Assay Measures
ADAMTS13 is the von Willebrand factor (VWF)-cleaving metalloprotease that trims ultra-high-molecular-weight VWF multimers and limits VWF-driven platelet aggregation. When ADAMTS13 function is severely reduced, circulating VWF multimers persist and can precipitate the microangiopathic thrombosis characteristic of thrombotic thrombocytopenic purpura (TTP).
This service quantifies ADAMTS13 proteolytic activity directly, rather than protein mass or antibody content, so that laboratories and biopharma teams can distinguish a functional enzyme deficiency from other causes of thrombotic microangiopathy. Results are expressed relative to a normal reference, which makes them comparable across serial samples and across studies.
VWF Substrate Cleavage
The assay reports the enzyme's ability to cleave a VWF-derived sequence, which is the defining functional property of ADAMTS13.
- Synthetic VWF fragment carries the cleavage site
- Proteolysis is the measured event
- Distinct from antigen or antibody readouts
FRET Fluorescence Signal
A fluorescent donor and quencher flank the cleavage site; cleavage separates the pair and increases fluorescence in proportion to activity.
- Kinetic or endpoint fluorescence measurement
- Signal quantified against a calibration curve
- Static liquid-phase in vitro format
Percent of Normal
Activity is reported as a percentage or in units relative to normal pooled plasma, supporting consistent interpretation across sites and timepoints.
- Calibrators and normal pooled plasma reference
- Serial-sample comparability
- Supports congenital versus acquired workup
Specimen Requirements
Specimen quality is the single largest source of variability in ADAMTS13 activity testing. The assay is validated on sodium citrate plasma, and collection in the wrong anticoagulant can artificially reduce measured activity. Double centrifugation to remove residual platelets is critical, because platelet contamination can produce spurious results.
The handling parameters below reflect the specimen conditions commonly specified for clinical ADAMTS13 activity testing. Project-specific acceptance criteria are confirmed during scoping so that collection, shipping, and storage align with the intended downstream use.
| Parameter | Typical Requirement | Rationale | Notes |
|---|---|---|---|
| Anticoagulant | Light-blue top tube, 3.2% sodium citrate | EDTA collection can artificially reduce measured activity | Confirm tube type at scoping |
| Preparation | Double-centrifuged platelet-poor plasma | Platelet contamination may cause spurious results | Aliquot into plastic vials |
| Volume | Approximately 2 mL plasma across two plastic vials | Supports initial testing and repeat or reflex testing | Each requested assay in its own vial |
| Freezing Window | Freeze promptly after collection | Preserves enzymatic activity before analysis | Exact window confirmed per project |
| Storage Temperature | Frozen, ideally at -40 degrees C or below | Maintains stability during storage and shipment | 20 degrees C acceptable where specified. |
| Stability | Frozen stability measured in years | Allows batched analysis of longitudinal samples | Verify against your collection protocol |
| Patient Preparation | Fasting preferred but not required | Reduces confounding from lipemia | Hyperlipidemia is a known interference |
| Collection Timing | Plasma exchange or transfusion may falsely normalize activity | Document therapy status with the sample |
How Engagement Works
Projects move from feasibility review to a defined scope, then to assay execution and a reportable dataset. Each step is documented so that results can be traced back to the specimen, the calibration, and the analysis conditions.
Consultation and Feasibility Review
We review your sample matrix, intended clinical or research question, and required reporting format, then confirm whether the FRET-based activity assay fits the study design.
Scope and Specimen Planning
Specimen collection, anticoagulant, centrifugation, aliquot volume, freezing, and shipping conditions are agreed in advance so that samples arrive within validated handling parameters.
Calibration and Assay Setup
Calibrators and a normal pooled plasma reference are prepared to build the activity curve, and assay conditions are set for the VWF peptide substrate cleavage reaction.
Fluorescence Measurement
Cleavage of the FRET substrate is monitored as increasing fluorescence, and the signal is converted to activity relative to the reference preparation using the calibration curve.
Why Teams Choose This Assay
ADAMTS13 activity sits at the center of the TTP diagnostic pathway, and the choice of method affects both sensitivity and how quickly a result can inform clinical or program decisions. A functional readout anchored to a normal reference gives teams a defensible basis for comparing samples, cohorts, and timepoints.
The service is built around the practical realities of coagulation testing: specimen integrity, calibration traceability, and clear interpretation boundaries.
Activity, Not Just Abundance
Because the readout is substrate cleavage rather than protein concentration, the assay captures functional deficiency that antigen testing alone may miss.
- Reports enzymatic capability directly
- Complements antigen and antibody testing
- Useful when protein level and function diverge
Reference-Anchored Results
Activity is expressed relative to calibrators and normal pooled plasma, producing values that can be tracked across serial draws and study arms.
- Percent or units of normal activity
- Calibration curve per run
- Consistent reporting format
Built for TTP Workflows
The assay supports the diagnosis and monitoring of congenital, immune, and acquired TTP, and low activity can trigger reflex inhibitor or antibody testing.
- Supports congenital versus acquired workup
- Flags samples for follow-up testing
- Interpretation guidance included
Service Scope
Scope is defined case by case after consultation. The table below describes the parameters that are typically customized; the final specification, including sample numbers, replicate structure, and reporting depth, is set in the project agreement.
Where a parameter is not fixed by the assay method itself, we confirm the appropriate setting with you rather than applying a default.
| Parameter | Typical Project Scope | Customization | Notes |
|---|---|---|---|
| Sample matrix | Citrated plasma as the validated matrix | Other matrices reviewed for feasibility | Matrix suitability confirmed at scoping |
| Sample number | Defined per project | Batched or staged submission supported | Scheduling agreed in advance |
| Replicate structure | Single or replicate wells as scoped | Replicate depth set by data needs | Affects precision reporting |
| Calibration | Calibrators plus normal pooled plasma reference | Reference preparation agreed per project | Curve included in the data package |
| Readout mode | Kinetic or endpoint fluorescence | Selected to match the study question | Both report substrate cleavage |
| Reporting units | Percent of normal or units | Format aligned to your downstream use | Consistent across the project |
| Reflex testing | Inhibitor or antibody testing when activity is low | Trigger threshold agreed in advance | Separate assay, ordered as follow-up |
| Data package | Results with supporting calibration and run data | Content and format scoped per project | Delivered as agreed |
Interpretation and Follow-Up
Activity results are most useful when read alongside the clinical picture. Severely reduced activity is highly indicative of TTP in an appropriate clinical setting, but not every patient with a clinical diagnosis of idiopathic TTP has severe deficiency, and some non-TTP conditions can also show markedly low activity.
Because of these overlaps, the assay is positioned as one component of an integrated diagnostic workup rather than a stand-alone confirmation.
When Activity Is Severely Reduced
Markedly low activity in a compatible clinical setting is highly indicative of TTP and typically prompts follow-up testing for an inhibitor or autoantibody.
- Supports the TTP diagnostic pathway
- Triggers reflex inhibitor or antibody testing
- Clinical correlation remains essential
When Results Are Not Clear-Cut
Low activity can also occur in hemolytic uremic syndrome, transplantation, liver disease, disseminated intravascular coagulation, sepsis, pregnancy, and with certain medications.
- TTP remains a clinical diagnosis
- Results interpreted with the full workup
- Context documented with each report
Known Assay Interferences
High endogenous VWF, hyperlipidemia, elevated bilirubin, and cleavage by other proteases can affect measured activity, as can recent plasma exchange or transfusion.
- EDTA collection reduces apparent activity
- Recent therapy may mask deficiency
- Interference notes accompany results
Assay Comparison
ADAMTS13 testing spans several distinct measurements that answer different questions. The comparison below clarifies where the activity assay sits relative to neighboring tests, so that the right panel is selected for the question at hand.
The activity assay is the functional measurement; the other assays provide complementary information and are typically ordered alongside or as follow-up.
| Assay | What It Measures | Typical Role | Relationship to Activity Assay |
|---|---|---|---|
| ADAMTS13 activity (FRET) | Cleavage of a VWF-derived substrate | Primary functional assessment | This service |
| ADAMTS13 inhibitor assay | Neutralizing immunoglobulins against ADAMTS13 | Follow-up when activity is low | Ordered after, not part of, the activity workflow |
| ADAMTS13 antibody assay | Binding autoantibodies to ADAMTS13 | Supports acquired TTP characterization | Complementary immunologic readout |
| ADAMTS13 antigen assay | ADAMTS13 protein concentration | Distinguishes low protein from low function | Can be normal despite low activity |
| VWF antigen | Von Willebrand factor quantity | Assesses VWF level | Different clinical question |
| VWF activity (ristocetin cofactor) | Platelet-dependent VWF function | Assesses VWF function | Not a measure of the protease |
Data, QC, and Support
Every project is delivered with the documentation needed to understand how a result was generated: the calibration curve, the reference preparation used, run conditions, and the reported activity value. Where a sample falls outside validated handling parameters, this is noted rather than silently reported.
Support is provided by a named scientific contact from project start, with milestone review calls and email responses within one business day.
Traceable Data Package
Results are delivered with the supporting calibration and run information so that reported activity values can be traced back to the assay conditions.
- Calibration and reference details
- Run conditions recorded
- Reporting format agreed in advance
Specimen Integrity Checks
Specimen suitability is evaluated before analysis, since anticoagulant choice, platelet contamination, and handling delays are established sources of error.
- Anticoagulant and preparation reviewed
- Handling deviations flagged
- Interference notes included
Scientific Contact
A named scientific contact is assigned at project start, with milestone review calls and email response within one business day for the duration of the project.
- Named contact from project start
- Milestone review calls
- Email response within one business day
Planning Your Project
The most common source of unusable ADAMTS13 activity data is specimen handling rather than the assay itself. Confirming collection tube, centrifugation, aliquot volume, and freezing logistics before the first draw prevents most repeat testing.
If your study involves serial sampling, longitudinal monitoring, or a mixed cohort, share the intended collection schedule during scoping so that batching and storage can be planned around it.
FAQ
What exactly does the ADAMTS13 activity assay measure?
It measures the enzyme's ability to cleave a von Willebrand factor-derived substrate. In the FRET format, a fluorescent donor and quencher flank the cleavage site, and proteolysis separates the pair to generate fluorescence that is proportional to activity. This is a functional readout, distinct from antigen assays that quantify protein concentration or antibody assays that detect immunoglobulins against the enzyme.
Which specimen type is required, and why does collection matter so much?
The assay is validated on sodium citrate plasma, typically collected in a light-blue top tube containing 3.2% sodium citrate. Collection in EDTA can artificially reduce measured activity, and residual platelets can cause spurious results, which is why double centrifugation to prepare platelet-poor plasma is critical. Each requested assay should have its own aliquot.
How are results reported, and what counts as abnormal?
Activity is quantified against calibrators and a normal pooled plasma reference and reported as a percentage or in units relative to normal. In clinical practice, activity below 10% is highly indicative of thrombotic thrombocytopenic purpura in an appropriate clinical setting, while results at or above roughly 70% are generally considered within the normal reference range. Clinical correlation remains essential.
What happens if my sample shows low activity?
Low activity commonly triggers follow-up testing for an ADAMTS13 inhibitor or autoantibody, which are separate assays measuring neutralizing or binding immunoglobulins rather than enzyme function. The trigger threshold and whether reflex testing is included are agreed during scoping, since the inhibitor and antibody assays answer a different question from the activity measurement itself.
Can I use this assay for samples that were collected after plasma exchange?
Recent plasma exchange or plasma transfusion may falsely normalize ADAMTS13 levels and mask a deficiency, so collection before replacement therapy is preferred where the clinical situation allows. If post-therapy samples must be used, document the therapy status with the sample so that the result can be interpreted with that context in mind.
What interferences should I be aware of?
Reported interferences include high levels of endogenous von Willebrand factor, hyperlipidemia, hyperbilirubinemia, and cleavage by other proteases. The assay is an in vitro method using a synthetic substrate in a static liquid environment, so measured activity may not fully reflect in vivo biological activity. Interference notes are provided alongside results.
References
- Deshpande SR, Tarawneh H, Deitelzweig C, et al. Rapid ADAMTS13 activity assays for thrombotic thrombocytopenic purpura: a systematic review and meta-analysis. Blood. 2025;146(2):233-246. View on PubMed
- Moore GW, Llusa M, Griffiths M, et al. ADAMTS13 Activity Measurement by ELISA and Fluorescence Resonance Energy Transfer Assay. Methods in molecular biology (Clifton, N.J.). 2023;2663:533-547. View on PubMed
Discuss Your ADAMTS13 Activity Project
Share your specimen type, collection protocol, and intended use, and we will confirm assay feasibility and define a project scope covering sample handling, calibration, reporting format, and follow-up testing options.