CurrentCurativePolicy CHP-OP-2026-008

ADAMTS13 Testing for Thrombotic Thrombocytopenic Purpura

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This policy governs medical-necessity review of ADAMTS13 activity, ADAMTS13 inhibitor, and anti-ADAMTS13 antibody testing for suspected or established immune-mediated or congenital TTP in all ages. It applies to outpatient laboratory testing and excludes inpatient thrombotic microangiopathy management, plasma exchange, caplacizumab, recombinant ADAMTS13, and germline ADAMTS13 sequencing.

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CurrentCurativePolicy CHP-OP-2026-008

ADAMTS13 Testing for Thrombotic Thrombocytopenic Purpura

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Policy Summary

PayerCurative

PolicyADAMTS13 Testing for Thrombotic Thrombocytopenic Purpura

Policy CodePolicy CHP-OP-2026-008

Change TypeNo material clinical or coverage changes

Effective DateN/A

Next Review DateN/A

Key ActionSubmit the clinical findings, pretest assessment, specimen timing, and management rationale for the applicable covered TTP testing pathway.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

<10 IU/dLSevere ADAMTS13 deficiency threshold

6-7High PLASMIC pretest probability

20 IU/dLRemission-risk monitoring threshold

3ADAMTS13 assay categories

4Medical-necessity pathways

Coverage Criteria

A. Initial ADAMTS13 Activity Testing

Covered when ALL of the following are met:

ALL of the following

The member has thrombocytopenia and MAHA (schistocytes or laboratory evidence of hemolysis), or a suspected TMA with organ involvement, and TTP is in the differential diagnosis. [S1]
The clinical pretest assessment is documented (PLASMIC, French score, or clinician judgment). Testing is supported at any pretest probability when TTP is a possible diagnosis. When probability is high, treatment must not wait for results. [S1, S2]
The specimen is collected before plasma infusion or plasma exchange whenever possible, and the timing of any plasma treatment relative to the draw is recorded. [S1]

B. ADAMTS13 Inhibitor or Anti-ADAMTS13 Antibody Testing

Covered when ANY of the following are met:

ANY of the following

ADAMTS13 activity is below 10 IU/dL, and immune-mediated TTP must be distinguished from congenital TTP. [S1]
Severe deficiency is confirmed, and the inhibitor or antibody result will guide immunosuppression or relapse-risk management. [S1, S2]

C. Monitoring During Treatment and Remission

Covered when ANY of the following are met:

ANY of the following

During an acute iTTP episode, to guide decisions about stopping caplacizumab or intensifying immunosuppression, as the treatment guideline describes. [S2, S3]
During clinical remission of iTTP, at intervals set by the treating hematologist (commonly monthly for the first 3 months after an episode, then every 3 months during the first year, then less often if activity stays normal). These results guide preemptive rituximab or other immunosuppression when activity falls below 20 IU/dL. [S2, S3]< 20 IU/dL
Suspected relapse or exacerbation (falling platelets, recurrent hemolysis, or new neurologic or cardiac symptoms), or a persistent or recurrent TMA, when the result will change management. [S1, S3]
Planning for pregnancy, elective surgery, or another high-risk period in a member with a history of iTTP or cTTP. [S2]

D. Family Evaluation

Covered when ALL of the following are met:

ALL of the following

The relative is a sibling of a person with confirmed cTTP, or a family-risk evaluation is documented by the treating hematologist or geneticist. [S1]
The result will guide surveillance, pregnancy management, or prophylaxis. Genetic testing is reviewed under Policy 10. [S1]

Continuation, Repeat Service, and Re-authorization

Continued remission monitoring, repeat services, and re-authorization are medically necessary when ALL of the following are met:

ALL of the following

The member has a confirmed history of iTTP or cTTP. [S1]
The testing interval is set by the treating hematologist. [S2, S3]
Each result guides monitoring intensity or preemptive treatment. [S2, S3]

The following services are outside this outpatient laboratory policy and are not covered under these criteria: inpatient management of thrombotic microangiopathy, plasma exchange, caplacizumab, recombinant ADAMTS13, and germline ADAMTS13 gene sequencing for suspected congenital TTP. Germline sequencing is reviewed under Policy 10.

Results drawn after plasma exposure must be interpreted with caution because treatment may affect the result. Repeat testing is supported when the result does not fit the clinical picture. The inhibitor assay and anti-ADAMTS13 antibody immunoassay should not both be reported for the same specimen unless the laboratory protocol and clinical question require both, such as a negative functional inhibitor result in suspected iTTP.

Population screening without clinical findings of TMA, a history of TTP, or a documented family-risk evaluation is not medically necessary because there is no established screening role. Requests in this circumstance are referred for physician review and are not denied by an automated system or non-physician reviewer.

ADAMTS13 testing as a biomarker for conditions without established clinical utility is not covered under this policy. Examples include COVID-19 severity, delayed cerebral ischemia after subarachnoid hemorrhage, hepatocellular carcinoma, sepsis, stroke prognosis, cardiovascular risk prediction, liver disease monitoring, and other non-TTP indications. These uses are considered experimental, investigational, or unproven under the plan's applicable standards.

Routine serial testing at a fixed interval is not medically necessary when the results will not change monitoring or treatment.

Inhibitor or anti-ADAMTS13 antibody testing is not medically necessary when ADAMTS13 activity is normal and there is no prior TTP diagnosis, because the result does not change the diagnosis.

Covered Testing Indications

Diagnosis of Suspected TTP or TMA With Organ Involvement

ADAMTS13 activity testing is covered for the following indication when the specimen-collection requirement is met.

Diagnosis of suspected TTP or TMA with organ involvement

Specimen collection and pretest assessment: The clinical pretest assessment is documented using the PLASMIC score, French score, or clinician judgment, and the specimen is collected before plasma infusion or plasma exchange whenever possible with the timing of any plasma treatment relative to the draw recorded.

Distinguishing Immune-Mediated From Congenital TTP

Functional inhibitor and anti-ADAMTS13 antibody testing is covered when ANY of the following are met.

Distinguishing TTP type or guiding management

Distinguish immune-mediated from congenital TTP:

Coding and Clinical Thresholds

ADAMTS13 activityCPT

85397

ADAMTS13 activity (functional activity assay)

Anti-ADAMTS13 antibodyCPT

83520

Anti-ADAMTS13 antibody (quantitative immunoassay)

ADAMTS13 inhibitorCPT

85335

ADAMTS13 inhibitor (functional inhibitor assay)

Severe ADAMTS13 deficiency

Activity thresholdBelow 10 IU/dL

Equivalent thresholdBelow 10 percent of normal

Clinical significanceDefines severe ADAMTS13 deficiency

High PLASMIC pretest probability

Score range6–7 on the PLASMIC score

Score typeA 7-point clinical score

Clinical significance

Provider Documentation and Action Items

Prior Authorization

Covered TTP Testing Indications

ADAMTS13 testing may be approved when medical necessity is established. Initial activity testing for diagnosis is covered when ALL criteria are met: the member has thrombocytopenia and MAHA (schistocytes or laboratory evidence of hemolysis), or suspected TMA with organ involvement, and TTP is in the differential; a clinical pretest assessment is documented (PLASMIC, French score, or clinician judgment); and the specimen is collected before plasma infusion or exchange whenever possible, with treatment timing recorded. Testing is supported at any pretest probability when TTP is possible; when probability is high, treatment must not wait for results.

Inhibitor or anti-ADAMTS13 antibody testing is medically necessary when ADAMTS13 activity is 10 IU/dL and immune-mediated TTP must be distinguished from congenital TTP, or when severe deficiency is confirmed and the result will guide immunosuppression or relapse-risk management.
Repeat activity testing, with inhibitor or antibody testing when indicated, is medically necessary during an acute iTTP episode when results guide caplacizumab or immunosuppression decisions; during iTTP remission at treating-hematologist-directed intervals; for suspected relapse or exacerbation or persistent/recurrent TMA when results will change management; before pregnancy, elective surgery, or another high-risk period in a member with iTTP or cTTP; and for congenital TTP monitoring when results guide prophylactic plasma or recombinant ADAMTS13 dosing or interval.
For family evaluation, testing is medically necessary when the relative is a sibling of a person with confirmed cTTP or a treating hematologist or geneticist documents family risk, and the result will guide surveillance, pregnancy management, or prophylaxis. Genetic testing is reviewed under Policy 10.

Clinical Background

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by severe ADAMTS13 deficiency. It commonly presents with microangiopathic hemolytic anemia, severe thrombocytopenia, and variable organ injury. ADAMTS13 activity below 10 IU/dL supports TTP in the appropriate clinical setting.

Definitions

Severe ADAMTS13 deficiency

DefinitionADAMTS13 activity below 10 IU/dL

Equivalent measureBelow 10 percent of normal

Use in TTP assessmentRepresents severe ADAMTS13 deficiency

PLASMIC score

Score structureA 7-point clinical score

Clinical factorsPlatelets below 30 × 10^9/L, hemolysis, no active cancer, no solid-organ or stem-cell transplant, MCV below 90 fL, INR below 1.5, and creatinine below 2.0 mg/dL

Clinical useA score of 6–7 indicates high pretest probability of severe ADAMTS13 deficiency

Frequency and Repeat-Testing Limits

ADAMTS13 activity with indicated inhibitor or antibody testing

First 3 months after an episodeTesting is commonly performed monthly

First yearTesting is commonly performed every 3 months

After the first yearTesting may occur less often if ADAMTS13 activity remains normal

ADAMTS13 testing

IntervalSet by the treating hematologist

Required use of each resultEach result must guide monitoring intensity or preemptive treatment

Covered continuation

Ordering Requirements

Documentation Required

Document the required family-risk evaluation

For family evaluation, document the family-risk evaluation by the treating hematologist or geneticist. The result must guide surveillance, pregnancy management, or prophylaxis.

Not Covered

Population screening is not covered when the individual has no clinical findings of thrombotic microangiopathy, no history of TTP, and no documented family-risk evaluation.

Use of ADAMTS13 testing for non-TTP biomarker applications is not covered when the use lacks established clinical utility, including other conditions or prognostic purposes outside TTP evaluation and management.

Routine serial testing at a fixed interval is not covered when there is no expected change in monitoring intensity or treatment based on the result.

Policy Summary

PayerCurative

PolicyADAMTS13 Testing for Thrombotic Thrombocytopenic Purpura

Policy CodePolicy CHP-OP-2026-008

Change TypeNo material clinical or coverage changes

Effective DateN/A

Next Review DateN/A

Key ActionSubmit the clinical findings, pretest assessment, specimen timing, and management rationale for the applicable covered TTP testing pathway.

SourceLink

On This Page

Monitoring of congenital TTP on prophylactic plasma or recombinant ADAMTS13 therapy, when the result will guide dosing or interval. [S2]

ADAMTS13 activity is below 10 IU/dL, and immune-mediated TTP must be distinguished from congenital TTP.

Guide immunosuppression or relapse-risk management: Severe ADAMTS13 deficiency is confirmed, and the inhibitor or antibody result will guide immunosuppression or relapse-risk management.

Monitoring Acute TTP, Remission, Relapse, and High-Risk Periods

Repeat testing is covered when ANY of the following clinically actionable circumstances applies.

Monitoring acute TTP, remission, relapse, high-risk periods, or congenital TTP therapy

Acute immune-mediated TTP: Testing guides decisions about stopping caplacizumab or intensifying immunosuppression during an acute immune-mediated TTP episode.
Clinical remission: Testing is performed at an interval set by the treating hematologist and guides preemptive rituximab or other immunosuppression when activity falls below 20 IU/dL.<20 IU/dL
Suspected relapse or exacerbation: There are falling platelets, recurrent hemolysis, new neurologic or cardiac symptoms, or persistent or recurrent TMA, and the result will change management.
High-risk period: Testing is performed for pregnancy, elective surgery, or another high-risk period in a member with a history of immune-mediated or congenital TTP.
Congenital TTP therapy: Testing monitors congenital TTP on prophylactic plasma or recombinant ADAMTS13 therapy, and the result will guide dosing or the treatment interval.

Family Evaluation for Congenital TTP Risk

Family evaluation is covered when ALL of the following are met.

Family evaluation for congenital TTP risk

Qualifying family risk: The relative is a sibling of a person with confirmed congenital TTP, or a family-risk evaluation is documented by the treating hematologist or geneticist.
Actionable result: The result will guide surveillance, pregnancy management, or prophylaxis.

Indicates high pretest probability of severe ADAMTS13 deficiency

ADAMTS13 activity for remission-risk management

Activity thresholdBelow 20 IU/dL

Monitoring contextUsed during clinical remission of immune-mediated TTP

Treatment guidanceMay guide preemptive rituximab or other immunosuppression

Partial ADAMTS13 remission

Lower boundaryAt least 20 IU/dL

Upper boundaryBelow the lower limit of normal

DefinitionADAMTS13 activity in this range constitutes partial remission

Documentation Required

Laboratory and Pretest Documentation

Submit the laboratory and pretest information supporting the request. Include the relevant laboratory results and the documented clinical pretest assessment when used.

Complete blood count, smear findings including schistocytes, LDH, haptoglobin, bilirubin, reticulocytes, creatinine, and INR.
PLASMIC score, French score, or other documented pretest assessment.

Documentation Required

Clinical Findings and Specimen Timing

Document the clinical findings and specimen timing that support testing, including organ involvement and any plasma exposure before collection.

Neurologic, cardiac, and renal findings.
Specimen collection time and timing of any plasma infusion or plasma exchange.
Results drawn after plasma exposure are interpreted with caution; a repeat test is supported when the result does not fit the clinical picture.

Documentation Required

Remission-Monitoring Records

For remission monitoring, document the clinical context and the plan showing how repeat ADAMTS13 results will guide care.

Date of the last iTTP episode.
Prior ADAMTS13 results.
Current treatment, including relevant immunosuppression or other therapy.
The treating hematologist's monitoring plan, including interval and how results will guide preemptive rituximab or other immunosuppression when activity falls below 20 IU/dL.

Documentation Required

Family-Evaluation Records

For family evaluation, document the relationship to the affected relative and the affected relative's diagnosis, along with how the result will guide care.

Identify the relative's relationship; a sibling of a person with confirmed cTTP qualifies, or family-risk evaluation must be documented by the treating hematologist or geneticist.
Document the affected relative's confirmed cTTP diagnosis and whether testing will guide surveillance, pregnancy management, or prophylaxis.

Denial Risk

Unindicated Population Screening

Population screening without clinical findings of TMA, a history of TTP, or a documented family-risk evaluation does not meet medical-necessity criteria and is referred for physician review rather than automated denial.

Do not submit ADAMTS13 testing as general population screening absent TMA findings, prior TTP, or documented family risk.

Denial Risk

Non-TTP Biomarker Use

ADAMTS13 testing used as a biomarker for conditions without established clinical utility does not meet medical-necessity criteria and is considered experimental, investigational, or unproven for those uses.

Examples include COVID-19 severity, delayed cerebral ischemia after subarachnoid hemorrhage, hepatocellular carcinoma, sepsis, stroke prognosis, cardiovascular risk prediction, liver disease monitoring, and other non-TTP indications.

Denial Risk

Non-Actionable Serial Testing

Routine serial ADAMTS13 testing at a fixed interval does not meet medical-necessity criteria when the results will not change monitoring or treatment.

Document the clinical decision or management change that the result is expected to inform; fixed-interval testing without an actionable purpose is not medically necessary.

Denial Risk

Unjustified Inhibitor or Antibody Testing

Inhibitor or anti-ADAMTS13 antibody testing does not meet medical-necessity criteria when ADAMTS13 activity is normal and no prior TTP diagnosis exists, because the result does not change the diagnosis.

Submit the activity result and prior TTP history when requesting inhibitor or antibody testing.

Billing Rule

Duplicate Inhibitor and Antibody Reporting

The inhibitor assay and antibody immunoassay must not both be reported for the same specimen unless the laboratory protocol and clinical question require both, such as a negative functional inhibitor result in suspected iTTP.

Report both assays on the same specimen only when justified by protocol and documented clinical need.
Interpret results drawn after plasma exposure with caution; a repeat test is supported when the result does not fit the clinical picture.

ADAMTS13 remission

Partial remissionADAMTS13 activity is at least 20 IU/dL but below the lower limit of normal

Complete remissionADAMTS13 activity is at or above the lower limit of normal

Measurement usedADAMTS13 activity defines the remission category

Microangiopathic hemolytic anemia (MAHA)

Core findingHemolytic anemia

Peripheral smearSchistocytes are present

Supporting laboratory findingsElevated LDH, low haptoglobin, and elevated indirect bilirubin or reticulocytes

Continued monitoring requires a confirmed history of immune-mediated or congenital TTP

ADAMTS13 inhibitor and anti-ADAMTS13 antibody assays

Same-specimen limitationThe inhibitor assay and antibody immunoassay are not both reported for the same specimen unless both are needed

ExceptionBoth may be reported when required by the laboratory protocol and clinical question

ExampleA negative functional inhibitor result in suspected immune-mediated TTP may warrant both assays