Currentmedical mutual - ohioPolicy AHS - G2105

Immunopharmacologic Monitoring of Therapeutic Serum Antibodies

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Defines coverage policy for measurement of serum drug concentrations and anti-drug antibodies for biologic therapies (primarily anti-TNF agents, ustekinumab, vedolizumab, and rituximab) and specifies which indications meet or do not meet coverage criteria for members of Medical Mutual - Ohio.

Policy Summary

Payermedical mutual - ohio

PolicyImmunopharmacologic Monitoring of Therapeutic Serum Antibodies

Policy CodePolicy AHS - G2105

Change TypeNo material change

Effective DateFeb 1, 2026

Last ReviewSep 4, 2025

Next Review DateN/A

Key ActionOrder drug and anti-drug antibody concentration testing for individuals with IBD, following frequency limits (once every two weeks) and document clinical status and testing intent.

SourceLink

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Currentmedical mutual - ohioPolicy AHS - G2105

Immunopharmacologic Monitoring of Therapeutic Serum Antibodies

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Policy Summary

Payermedical mutual - ohio

PolicyImmunopharmacologic Monitoring of Therapeutic Serum Antibodies

Policy CodePolicy AHS - G2105

Change TypeNo material change

Effective DateFeb 1, 2026

Last ReviewSep 4, 2025

Next Review DateN/A

Key ActionOrder drug and anti-drug antibody concentration testing for individuals with IBD, following frequency limits (once every two weeks) and document clinical status and testing intent.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

Every 2 wksCovered frequency

10 listedDrugs not covered outside IBD

≈50%Secondary failure rate

≥2 µg/mLInfliximab trough assoc.

73.6%Proactive TDM control

09/04/2025Last reviewed

Coverage Criteria

Covered Indication — Inflammatory Bowel Disease (IBD)

Covered when ALL of the following are met

IBD testing frequency: For individuals with inflammatory bowel disease (IBD), drug and/or antibody concentration testing once every two weeks for anti-TNF therapies, vedolizumab therapy, or ustekinumab therapy meets coverage criteria.testing every 2 weeks

From policy III(1).

Not Covered — Other Indications

The following does NOT meet coverage criteria

Non-IBD inflammatory indications: For individuals with conditions other than IBD (e.g., spondyloarthritis, rheumatoid arthritis, psoriatic arthritis, and psoriasis), drug and/or antibody concentration testing for anti-TNF therapies does not meet coverage criteria.

From policy III(2).

Not Covered — All Other Situations / Drugs

Measurement does not meet coverage criteria for any of the following drugs in situations not addressed above

Listed drugs not covered in other situations: Measurement of serum drug levels and/or antibodies to the drugs does not meet coverage criteria for adalimumab, certolizumab, etanercept, golimumab, infliximab, infliximab-dyyb, infliximab-abda, rituximab, ustekinumab, and vedolizumab when not for IBD as specified.

From policy III(3) subitems a-j.

Appropriate clinical scenarios for TDM

Guideline/consensus-based scenarios where TDM is appropriate:

Anti-TNF responders and maintenance: It is appropriate to order drug/antibody concentration testing in responders at the end of induction for all anti-TNFs and at least once during maintenance.refer to agent-specific troughs

Consensus statements 1-2 (anti-TNFs).

Primary non-responders and secondary loss of response (reactive): Reactive TDM is appropriate for primary non-responders at end of induction and for confirmed secondary loss of response for anti-TNFs and other biologics; results should guide whether to optimize therapy or switch agents.

Consensus items 3-4; see consensus statements for vedolizumab/ustekinumab.

Agent-specific trough targets: Minimal trough concentrations are recommended for certain agents (e.g., infliximab post-induction >3 μg/mL and maintenance >3 μg/mL; adalimumab week 4 ≥5 μg/mL and maintenance >5 μg/mL; certolizumab week 6 >32 μg/mL; golimumab week 6 ≥2.5 μg/mL).see thresholds module

Consensus coverage criteria for TDM

Consensus statements support TDM in specific scenarios:

Reactive TDM indications: Reactive TDM should be performed in patients with confirmed primary non-response to anti-TNF therapy and in patients with confirmed secondary loss of response to anti-TNF and other biologics (vedolizumab, ustekinumab) prior to switching therapy.

High agreement across consensus statements.

Proactive TDM indications: Proactive TDM should be performed post-induction for patients treated with anti-TNF therapy and at least once during maintenance; proactive TDM can follow reactive TDM and is particularly important in more severely active patients or those with higher drug clearance.

Consensus recommends proactive monitoring mainly for anti-TNFs (chunks 38-39).

Infliximab secondary loss management: Do not consider treatment discontinuation for secondary loss of response to infliximab until a trough concentration of at least 10–15 μg/mL is achieved.>=10-15 μg/mL

Consensus statement specifying threshold (chunk 36).

Testing for serum anti‑TNF drug levels and anti‑drug antibodies is limited by this policy to inflammatory bowel disease. For other inflammatory conditions (for example, spondyloarthritis, rheumatoid arthritis, psoriatic arthritis, and psoriasis) such testing for anti‑TNF therapies does not meet coverage criteria and will be denied unless otherwise covered by the member's benefits or applicable government policy.

The National Institute for Health and Clinical Excellence (NICE) concluded that ELISA kits show promise for therapeutic monitoring of TNF‑alpha inhibitors but that there is insufficient evidence to recommend routine adoption; NICE recommends ELISA use primarily in research or data‑collection settings and highlights specific commercial kits referenced in their guidance.

Consensus guidance notes that when patients develop high‑titer anti‑drug antibodies with undetectable trough drug levels, the appropriate management is to switch therapy rather than escalate the current anti‑TNF dose. When switching within class after immunogenic failure, adding an immunomodulator is advised to reduce risk of recurrent immunogenicity.

Outside the situations explicitly covered for inflammatory bowel disease, measurement of serum drug concentrations and/or antibodies to the listed agents does not meet coverage criteria. The drugs named in the policy include adalimumab, certolizumab, etanercept, golimumab, infliximab (and biosimilars), rituximab, ustekinumab, and vedolizumab when ordered for indications or circumstances not specified as covered.

Some guideline bodies do not endorse routine proactive therapeutic drug monitoring for all patients in remission. For example, the ACG states there is insufficient evidence to support proactive TDM in all unselected patients with ulcerative colitis in remission, and NICE similarly notes limited evidence for routine proactive adoption of monitoring outside research contexts.

The evidence base for proactive TDM is strongest for anti‑TNF agents; by contrast, consensus statements and reviews indicate that more data are needed to support routine proactive TDM for biologics other than anti‑TNF (for example, vedolizumab and ustekinumab), so routine proactive monitoring for those agents is not supported by current consensus.

For context when applying these coverage rules, the policy specifically references the following drugs: adalimumab, certolizumab, etanercept, golimumab, infliximab, infliximab‑dyyb, infliximab‑abda, rituximab, ustekinumab, and vedolizumab. These agent names are used throughout the criteria and coding sections to define which measurements are covered or not covered.

Covered Indications and Scenarios

Inflammatory bowel disease (IBD) — Drug and/or antibody concentration testing once every two weeks for anti-TNF therapies, vedolizumab, or ustekinumab meets coverage criteria.

Frequency limit for IBD testing: Drug and/or antibody concentration testing for anti-TNF therapies, vedolizumab, or ustekinumab is allowed once every two weeks for individuals with IBD.once every two weeks

From policy III(1).

Reactive testing for primary non-response or secondary loss of response to biologic therapy — Consensus statements strongly endorse reactive TDM

Reactive TDM endorsement: Consensus statements strongly endorse reactive TDM for primary non-response and for confirmed secondary loss of response across anti-TNF agents and other biologics; reactive TDM should be performed prior to switching therapy.

High vote agreement in consensus statements (chunks 36-37).

Frequency Limits and Testing Schedule

inv-41: drug and/or antibody concentration testing for anti-TNF, vedolizumab, ustekinumab — once every two weeks

Frequency limitDrug and/or antibody concentration testing for anti-TNF therapies, vedolizumab, or ustekinumab: once every two weeks.

Applies toIndividuals with inflammatory bowel disease (IBD).

Not applicable toIndications other than IBD (e.g., spondyloarthritis, rheumatoid arthritis, psoriatic arthritis, psoriasis).

inv-42: drug and anti-drug antibody concentrations — At least once during maintenance; at end of induction

Minimum timingAt least once during maintenance (proactive monitoring).

End of inductionTesting appropriate at the end of induction for responders and primary non-responders to anti-TNFs.

Provider Actions and Clinical Guidance

Prior Authorization

IBD testing allowed; other indications not covered

For members with inflammatory bowel disease (IBD), measurement of serum drug levels and/or anti‑drug antibodies for anti‑TNF agents, vedolizumab, or ustekinumab meets coverage when requested at the allowed frequency; testing for these agents for indications other than IBD does not meet coverage.

Covered frequency: once every two weeks for drug and/or antibody concentration testing for anti‑TNF therapies, vedolizumab, or ustekinumab
Testing for anti‑TNF drug/antibody concentrations for non‑IBD indications (e.g., RA, psoriatic arthritis, spondyloarthritis, psoriasis) does not meet coverage

Documentation Required

Include clinical scenario and agent-specific target levels on orders

When ordering TDM, indicate the clinical scenario (reactive vs proactive) and reference guideline-recommended trough targets for the agent requested (for example, infliximab and adalimumab targets cited by consensus/ACG guidance). Reactive testing is recommended for active disease, primary non‑response, or confirmed secondary loss of response.

Coding and Test Codes

Drugs mentionedmixed

adalimumab	drug named in policy
certolizumab	drug named in policy
etanercept	drug named in policy
golimumab	drug named in policy
infliximab	drug named in policy
infliximab-dyyb	biosimilar named in policy
infliximab-abda	biosimilar named in policy
rituximab	drug named in policy
ustekinumab	drug named in policy
vedolizumab	drug named in policy

Procedure and proprietary test codes referencedCPT | HCPCS | mixed

80145	Adalimumab
80230	Infliximab
80280	Vedolizumab (listed with infliximab in text)
80299	Quantitation of therapeutic drug, not elsewhere specified
82397	Chemiluminescent assay
84999	Unlisted chemistry procedure
0515U	Proprietary Procise IFXT™ (infliximab) assay (FDA/Proprietary test identifier)

inv-14: Infliximab trough concentration — >= 2 µg/mL associated with higher probability of remission (study thresholds cited)

Association with remissionInfliximab trough concentration ≥ 2 µg/mL (studies cite ≥2.1 µg/mL and maintenance >2 µg/mL) associated with higher probability of clinical and endoscopic remission.

Supporting evidenceVan Stappen et al. reported TC ≥2.1 µg/mL associated with mucosal healing (LFA vs ELISA).

Meta-analysisMoore et al. systematic review: maintenance trough >2 µg/mL linked to greater likelihood of remission and mucosal healing.

inv-15: IFX trough targets used in proactive regimen — 3-7 µg/mL for Crohn's disease; 5-10 µg/mL for ulcerative colitis

Crohn's disease targetInfliximab trough target used in proactive regimens: 3–7 µg/mL for Crohn's disease.

Ordering Requirements

Note

Be aware many TDM assays are CLIA LDTs (high‑complexity)

Many laboratories perform proprietary or laboratory‑developed TDM assays that are regulated as high‑complexity LDTs under CLIA; ordering clinicians should be aware assays may be lab‑specific and not FDA‑cleared.

LDTs are regulated under CLIA '88 as high‑complexity tests and are not FDA‑cleared/approved
Identify the lab/method on the order when relevant to interpretation

Prior Authorization

Order testing only for guideline‑specified clinical scenarios

Order TDM when guideline‑specified clinical scenarios are present: active disease, primary non‑response at end of induction, or confirmed secondary loss of response; proactive orders are appropriate at end of induction and at least once during maintenance for anti‑TNFs.

Reactive TDM is appropriate for flares, primary non‑response, or secondary loss of response
Proactive testing: end of induction and at least once during maintenance for anti‑TNF agents

Not Covered

Testing for anti‑TNF drug and/or antibody concentrations for indications other than inflammatory bowel disease (for example, rheumatoid arthritis, spondyloarthritis, psoriatic arthritis, and psoriasis) is explicitly not covered under this policy and will be denied when submitted for those indications.

The NICE guidance cited in this policy states that ELISA‑based therapeutic monitoring for TNF‑alpha inhibitors has insufficient evidence for routine clinical adoption and recommends that such testing be conducted within research or data‑collection settings until more robust clinical‑effectiveness data are available.

Consensus panels conclude that while proactive TDM is supported for anti‑TNF agents, there is insufficient evidence to endorse routine proactive therapeutic drug monitoring for biologics other than anti‑TNF, and therefore routine proactive testing for those other agents is not supported by current consensus.

Background

Tumor necrosis factor inhibitors and other biologic therapies are widely used to treat inflammatory disorders such as inflammatory bowel disease, rheumatoid arthritis, spondyloarthritis, and psoriasis. Immunogenicity (development of anti‑drug antibodies) and low drug concentrations can contribute to secondary loss of response, which underpins the rationale for therapeutic drug monitoring (TDM) to guide dose optimization or switching of biologic therapy.

Definitions

inv-31: TDM / Therapeutic drug monitoring — Measurement of serum drug concentrations and anti-drug antibodies

DefinitionMeasurement of serum drug concentrations and anti-drug antibodies to optimize dosing and manage loss of response to biologic therapies.

PurposeUsed to guide dose adjustment, switching therapies, and to interpret clinical non-response or loss of response.

Common assaysIncludes ELISA, homogeneous mobility shift assay (HMSA), lateral-flow assays (LFA) and other quantitative immunoassays used in clinical practice.

inv-32: Anti-drug antibodies (ADAbs) — Antibodies formed against biologic therapy

DefinitionAntibodies formed against biologic therapy (e.g., antibodies-to-infliximab, antibodies-to-adalimumab) that may reduce drug efficacy or cause adverse effects.

Clinical relevance

Revision History

2026-02-01Policy effectiveLatest

Policy effective date published for Immunopharmacologic Monitoring of Therapeutic Serum Antibodies (AHS - G2105).

2025-09-04Last reviewed

Policy last reviewed on 2025-09-04 (administrative and clinical review noted).

2025-09-04Revision

Policy Summary

Payermedical mutual - ohio

PolicyImmunopharmacologic Monitoring of Therapeutic Serum Antibodies

Policy CodePolicy AHS - G2105

Change TypeNo material change

Effective DateFeb 1, 2026

Last ReviewSep 4, 2025

Next Review DateN/A

Key ActionOrder drug and anti-drug antibody concentration testing for individuals with IBD, following frequency limits (once every two weeks) and document clinical status and testing intent.

SourceLink

On This Page

ACG/consensus guidance (chunks 30-33).

Vedolizumab and ustekinumab testing: For vedolizumab and ustekinumab, testing is appropriate in non-responders at end of induction and in confirmed secondary loss of response; current evidence is insufficient to define specific induction/maintenance concentration targets beyond confirming detectable drug.detectable drug

Emerging data but insufficient specific thresholds (chunk 34).

Immunogenicity-driven management: High-titer anti-drug antibodies with undetectable troughs should prompt switching therapy rather than dose escalation; low-titer antibodies may be managed with optimization (dose escalation, interval shortening, or adding an immunomodulator).

Consensus statements on immunogenicity and management (chunks 41-42).

Proactive testing at end of induction and at least once during maintenance for anti-TNF agents — Consensus supports proactive TDM for anti-TNFs

Proactive anti-TNF testing: Consensus supports proactive TDM for anti-TNF agents: perform TDM post-induction and at least once during maintenance; proactive monitoring is most useful in more severely active patients or those with higher drug clearance.at least once during maintenance; post-induction

Consensus statements 10-13 and anti-TNF recommendations (chunks 38,26).

Primary nonresponse to biologic therapy and secondary loss of response — Reactive TDM recommended prior to switching or altering therapy; proactive TDM recommended post‑induction and at least once during maintenance

Reactive TDM before switching: Reactive TDM is recommended for primary nonresponse and for secondary loss of response to biologics (anti-TNF, vedolizumab, ustekinumab) prior to switching or altering therapy.

Consensus statements support reactive testing across agents (chunks 36-37).

Proactive TDM post-induction and maintenance: Proactive TDM is recommended post-induction and at least once during maintenance for anti-TNF therapies; evidence is limited for proactive TDM for vedolizumab and ustekinumab beyond confirming detectable drug.post-induction; at least once during maintenance

Consensus supports proactive anti-TNF monitoring; less evidence for other biologics (chunks 38,34).

ContextRecommended by consensus statements as part of proactive TDM strategy for anti-TNF agents.

inv-43: anti‑TNF drug level (proactive monitoring) — At least once during maintenance (proactive TDM)

Proactive monitoring frequencyAt least once during maintenance for patients treated with anti‑TNF therapy (proactive TDM).

Proactive timingPerformed post-induction and utilized at least once during maintenance; may follow reactive TDM.

Priority populationMost important in more severely active patients or those with higher drug clearance.

Reference minimal trough targets where applicable (e.g., infliximab post‑induction >3 µg/mL; adalimumab week 4 ≥5 µg/mL; ACG lists infliximab >5 µg/mL and adalimumab >7.5 µg/mL as minimal therapeutic troughs)
Specify whether the request is for reactive TDM (active disease, primary non‑response, secondary loss) or proactive timing (end of induction, once during maintenance)

Billing Rule

Use appropriate CPT/HCPCS codes and document testing intent

Use the procedure codes referenced in the policy when submitting claims and include supporting documentation with the claim. Providers must select the appropriate CPT/HCPCS code for the specific assay or proprietary test used.

Examples of referenced codes: 80145, 80230, 80280, 80299, 82397, 84999, and proprietary code 0515U (Procise IFXT™)
Attach clinical documentation that justifies the test (see ordering and documentation requirements)

Step Therapy

Follow algorithm‑based management informed by drug and antibody levels

Clinical algorithms that combine measured drug concentrations and anti‑drug antibody results may be used to guide management decisions instead of routine empiric dose escalation; such algorithm‑based approaches have been shown to reduce costs without worsening clinical efficacy in trials.

Algorithms informed by combined drug and antibody measurements can guide whether to intensify dose, add immunomodulator, or switch agents
Evidence (Steenholdt et al.) supports algorithm-based interventions versus routine dose intensification

Note

Use TDM results to guide switching or dose adjustments

Therapeutic drug monitoring (drug level and anti‑drug antibody results) may be used to inform decisions to switch biologic therapy or adjust dosing; document how results will influence the planned therapeutic change.

Patients with strongly positive antibodies are more likely to be switched to another biologic rather than dose‑adjusted
Document whether results will prompt optimization (dose/interval change) or switching of therapy

Step Therapy

Do not dose‑escalate for high‑titer anti‑drug antibodies; switch therapy

Do not escalate dose for patients with secondary loss of response due to high‑titer anti‑drug antibodies; instead switch to a different therapy (within‑ or out‑of‑class) per consensus guidance.

High‑titer anti‑drug antibodies with undetectable troughs require change of therapy rather than dose escalation
When switching within class after antibody‑mediated loss, consider adding an immunomodulator to the subsequent anti‑TNF

Documentation Required

Collect and document true trough timing (≤24 hours pre‑dose)

Collect trough specimens for drug concentration testing no more than 24 hours before the patient's next scheduled dose; document timing of specimen relative to dosing on the order and report.

Trough level defined as the lowest drug concentration and should be assessed ≤24 hours prior to next scheduled dose
Record collection time and the timing of the last dose on the requisition

Documentation Required

Document clinical status and testing intent on the order

When ordering, document the patient’s clinical status (active disease, remission, primary non‑response, or secondary loss of response) and the intent of testing (reactive vs proactive) to support medical necessity.

Indicate whether testing is reactive (e.g., flare, non‑response) or proactive (end of induction, once in maintenance)
Document objective evidence of active disease or reason for testing to support coverage

Documentation Required

Use the same TDM assay longitudinally when feasible

Whenever possible, follow patients longitudinally using the same TDM assay until commercial assays are cross‑validated and standardized; note the assay used in the result documentation.

Document the specific assay/method used (e.g., ELISA, LFA, HMSA or proprietary assay) on reports and orders
Avoid switching assays for a patient unless cross‑validation is available

Denial Risk

Non‑IBD indications will result in non‑coverage/denial

Testing for drug and/or antibody concentrations for anti‑TNF therapies is not covered for non‑IBD indications (such as RA, psoriatic arthritis, spondyloarthritis, and psoriasis) and may be denied if submitted for these diagnoses.

Claims for anti‑TNF drug or antibody testing submitted for non‑IBD indications do not meet coverage criteria and are subject to denial

Denial Risk

NICE: insufficient evidence to adopt routine ELISA monitoring

NICE concluded that ELISA kits show promise but there is currently insufficient evidence to recommend routine adoption of ELISA tests for therapeutic monitoring of TNF‑alpha inhibitors; use of ELISA for these indications should be limited to research/data collection.

NICE named specific ELISA tests (Promonitor, IDKmonitor, LISA‑TRACKER, RIDASCREEN, MabTrack) and recommends use in research settings due to insufficient evidence for routine adoption

Denial Risk

Government coverage policies take precedence over this Policy

If this Policy conflicts with applicable government coverage (e.g., LCDs or NCDs), the government policy governs determinations; noncompliance with such government policies may lead to denial.

Follow Medicare/Medicaid LCDs and NCDs when they differ from this policy; agency determinations take precedence

Ulcerative colitis targetInfliximab trough target used in proactive regimens: 5–10 µg/mL for ulcerative colitis.

Proactive regimen detailsRegimen measured IFX trough before the fourth infusion and subsequently every two infusions to maintain targets.

inv-16: Selected biologic trough concentrations — Examples for infliximab, adalimumab and others

Infliximab (post-induction/maintenance)Post-induction minimal trough >3 µg/mL; concentrations >7 µg/mL associated with increased likelihood of mucosal healing.

AdalimumabWeek 4 minimal concentration ≥5 µg/mL; concentrations >7 µg/mL associated with mucosal healing; maintenance trough >5 µg/mL for remission.

Certolizumab pegol and golimumabCertolizumab week 6 >32 µg/mL (maintenance ≥15 µg/mL); golimumab week 6 ≥2.5 µg/mL (maintenance >1 µg/mL).

inv-17: Infliximab trough concentration recommended threshold (context) — >= 10-15 µg/mL referenced in guidance before considering discontinuation for secondary loss

Threshold before discontinuation>= 10–15 µg/mL: infliximab trough concentration recommended to be achieved before considering treatment discontinuation for secondary loss of response.

Consensus contextStatement originates from consensus recommendations on reactive TDM for secondary loss of response to infliximab.

ApplicationUsed when evaluating whether to abandon infliximab in active disease; supported by high vote agreement in consensus statements.

Documentation Required

Document assay method when ordering LDT TDM assays

Recognize that many available assays are laboratory‑developed tests (LDTs) regulated under CLIA as high‑complexity tests; ordering clinicians should document the assay if assay‑specific cutoffs or interpretations are used.

LDTs are regulated by CMS under CLIA '88 and are not FDA‑cleared; assay‑specific cutoffs may vary between labs
Include assay identification on orders when results will inform management

Anti-drug antibodies are more clinically relevant when trough drug concentrations are undetectable; high-titer antibodies generally prompt switching therapy.

Assay cutoffsSpecific high‑titer cutoffs reported for some assays (e.g., ANSER 10 U/mL; RIDAscreen 200 ng/mL; InformTx/Lisa Tracker 200 ng/mL for infliximab).

inv-33: Proactive TDM — Scheduled measurement of drug and antibody concentrations (e.g., end of induction and during maintenance)

DefinitionScheduled measurement of drug and antibody concentrations (for example, at end of induction and during maintenance) to optimize therapy even in the absence of clinical worsening.

Typical timingPost-induction measurement and at least once during maintenance; may include measurement before the fourth infusion and periodically thereafter in proactive protocols.

Intended benefitAims to prevent loss of response, increase mucosal healing rates, and reduce surgeries compared with non-TDM management in some studies.

inv-34: Reactive TDM — Measurement in response to clinical events such as primary non-response or secondary loss of response

DefinitionMeasurement of drug and antibody concentrations in response to clinical events such as primary non-response or secondary loss of response to guide immediate therapeutic decisions.

When to useRecommended prior to switching therapy for primary non-response or confirmed secondary loss of response to anti-TNFs and other biologics.

RoleUsed to determine whether to optimize dosing, add an immunomodulator, or switch agents based on drug level and antibody status.

inv-35: Low‑titer vs high‑titer anti‑drug antibodies — Low‑titer may be overcome by optimization; high‑titer often requires switching

Clinical implicationsLow‑titer anti‑drug antibodies may be overcome with treatment optimization (dose escalation, interval shortening, or adding an immunomodulator).

High‑titer managementHigh‑titer anti‑drug antibodies, especially with undetectable troughs, usually require switching to a different therapy rather than dose escalation.

Assay-specific cutoffsFor infliximab: ANSER high‑titer = 10 U/mL; RIDAscreen and InformTx/Lisa Tracker cutoffs = 200 ng/mL; other assays lack validated high‑titer cutoffs.

inv-36: Proactive vs reactive TDM — Definitions and timing distinctions

Proactive vs ReactiveProactive TDM: scheduled post‑induction and at least once during maintenance to optimize dosing; Reactive TDM: performed in response to primary non-response or secondary loss of response.

Relative evidenceConsensus supports proactive TDM primarily for anti‑TNF agents; reactive TDM has broad consensus across biologics.

Operational differenceProactive uses routine scheduled sampling (even when clinically stable); reactive is triggered by clinical deterioration or lack of response.

Document text updated with consensus-based guidance and coding table revisions reflected in current version; administrative header notes updated.