The technology

The RIDASCREEN IFX Monitoring test (R-Biopharm) is an enzyme-linked immunosorbent assay (ELISA) to measure the levels of infliximab (both the branded Remicade and its biosimilars Inflectra and Remsima) in human plasma or serum samples. The RIDASCREEN Anti‑IFX Antibodies test is also an ELISA to detect antibodies against infliximab. This briefing focuses on their use to guide treatment with infliximab when used to treat inflammatory bowel disease (IBD).

People process infliximab differently, such that some people's IBD responds well to treatment whereas others have a lesser response or no response at all (primary non-responders). Some people's IBD initially responds to infliximab treatment but then stops (secondary loss of response). The RIDASCREEN IFX Monitoring test measures the amount of available (free) infliximab in the blood to determine whether the levels are high enough for infliximab to be an effective treatment for IBD. If the levels are too low, the RIDASCREEN Anti‑IFX Antibodies test can be used to determine if this is because antibodies against infliximab are present in the blood.

Each RIDASCREEN test comes in a single kit, which includes a 96-well microtitre plate, 12 single‑use 8-microwell strips, and all necessary reagents for up to 40 duplicate or 80 singlicate tests on serum or plasma samples. For every test, 16 microwells are used for calibration and quality control using 6 standards and 2 control samples in duplicate. Other reagents provided with the kit include diluent, conjugates, substrate, wash fluid and a stop reagent.

Table 1 Comparative specifications of the RIDASCREEN tests


RIDASCREEN Anti‑IFX Antibodies

ELISA type

Sandwich ELISA

Bridging-type ELISA

Analyte detected

Free infliximab drug

Free anti-infliximab antibodies

Microwell coating

TNF‑alpha molecules


Detection reagents

Conjugate: peroxidase conjugated, monoclonal antibody (MA-IFXB7)

Substrate: hydrogen peroxide/ tetramethylbenzidine

Conjugate 1: biotin conjugated infliximab

Conjugate 2: peroxidase conjugated streptavidin

Substrate: hydrogen peroxide/ tetramethylbenzidine


Low positive: 30 ng/ml IFX

Positive: 70 ng/ml IFX

Low positive: 0.375 ng/ml Anti‑IFX antibody (MA-IFX10F9)

Positive: 3 ng/ml Anti‑IFX antibody (MA-IFX10F9)

Sample dilutions/
measurement range

1:100 / 0.5 to 12 micrograms/ml IFX

1:400 / 2.0 to 48 micrograms/ml IFX

1:25 / 2.5 to 125 ng/ml ATI

1:200 / 20 to 1,000 ng/ml ATI

Total incubation times

1 hour 40 minutes

1 hour 55 minutes

Abbreviations: ATI, antibodies to infliximab; ELISA, enzyme-linked immunosorbent assay; IFX, infliximab; TNF, tumour necrosis factor.

Please refer to the manufacturer's instructions for further detailed information on the tests.

Both tests need additional equipment to be used, specifically: precision micropipettes and standard pipettes, a microplate washer or multichannel pipette, a 37°C incubator and a spectrophotometer (450 nm) or microplate reader (for manual mode). This equipment is readily available in most pathology laboratories. The manufacturer can supply its own microplate reader, the Dynex DS2, if needed.

For each sample, the concentration of free infliximab or antibodies against infliximab is calculated using the 6 standards. Laboratories with semi-automated ELISA platforms will have the software to do this calculation automatically. However, the evaluation software RIDASOFT is available for free from the company if needed.

R-Biopharm has recently developed RIDA QUICK IFX Monitoring, which is a rapid lateral flow test to quantify infliximab trough levels within 20 minutes. The company also has a number of other ELISAs including RIDASCREEN ADM Monitoring for the quantitative determination of another TNF‑alpha inhibitor, adalimumab. However, these tests are beyond the scope of this briefing.


The tests are designed to guide further treatment using information on how a person's body processes and responds to infliximab, which is known to vary significantly between people. This may be more precise than current management options such as empiric dose intensification, switching agents or immunomodulation.

RIDASCREEN tests are the commercially available products which were described in the NICE diagnostics guidance on therapeutic monitoring of TNF-alpha inhibitors in Crohn's disease as the Leuven in-house ELISA.

Current NHS pathway or current care pathway

The current diagnostic and care pathways for Crohn's disease are described in the NICE diagnostics guidance on therapeutic monitoring of TNF-alpha inhibitors in Crohn's disease. NICE technology appraisal guidance on infliximab, adalimumab and golimumab describes the current management pathway for ulcerative colitis.

NICE recommends initial induction treatment with infliximab of intravenous infusion at 0, 2 and 6 weeks. No further treatment should be offered if the disease does not respond to this induction treatment. The specialist commentators who contributed to this briefing indicated that current practice would include measurement of infliximab levels in people whose disease has not responded at this point, using a test such as RIDASCREEN IFX Monitoring.

People whose disease responds to the induction treatment will progress to maintenance treatment. If their disease stops responding over time, treatment decisions are based on 'trial and error'. This includes shortening the interval between dosing, increasing the dose, switching to a different drug treatment and immunomodulation.

NICE diagnostics guidance on therapeutic monitoring of TNF-alpha inhibitors in Crohn's disease considers the use of these tests during the maintenance phase of treatment, but concludes that there is insufficient evidence to recommend their routine use in the NHS.

The RIDASCREEN Anti‑IFX Antibodies test cannot measure antibodies against infliximab in samples that have a high level of infliximab: it can only be done if there is less than 1 microgram/ml in the sample. Therefore, a reflex testing strategy should be used. The RIDASCREEN IFX Monitoring test is done first; if the drug is undetectable, the Anti‑IFX Antibodies test is used.

NICE is aware of the following CE-marked devices that appear to fulfil a similar function to the RIDASCREEN IFX Monitoring and Anti‑IFX Antibodies tests:

Population, setting and intended user

The RIDASCREEN tests would be used in addition to existing investigations to guide treatment of IBD with infliximab. Treatment with infliximab is managed by clinicians with experience of tumour necrosis factor‑alpha (TNF-alpha) inhibitors and of managing IBD, such as gastroenterologists.

The tests would be done after the induction treatment and during maintenance treatment, before infusion with infliximab, in a hospital setting. They would be done in clinical laboratories and run by qualified laboratory staff with appropriate training on the test and system. The laboratory staff should work closely with the treating or referring clinician, in a network, to ensure appropriate use of the tests and interpretation of the results.


Technology costs

Each tests comes with the necessary reagents for 40 duplicate or 80 singlicate tests on plasma or serum samples. The costs of the tests per patient are:

  • IFX Monitoring: duplicate processing (40 samples), £19.88

  • IFX Monitoring: singlicate processing (80 samples), £9.94

  • Anti‑IFX Antibodies: duplicate processing (40 samples), £24.65

  • Anti‑IFX Antibodies: singlicate processing (80 samples), £12.33.

These costs depend on workload: if there are not enough samples for a full batch, the kit will need to be split. More patient samples (48 singlicate and 88 duplicate) could be processed if a laboratory can verify the use of standards and controls in singlicate.

These costs also do not include the additional equipment needed (pipettes, a microplate washer, an incubator and a spectrophotometer or microplate reader), but this equipment is readily available in most pathology laboratories. Staff costs, maintenance contracts and additional quality assurance needs are also not included. These costs would differ between manual and automated tests.

Table 2 Current costs of the RIDASCREEN tests and components



Additional information

RIDASCREEN IFX Monitoring test kit


Includes all necessary reagents, 1 96-well microtitre plate and 12 single-use 8‑microwell strips

RIDASCREEN Anti‑IFX Antibodies test kit


Includes all necessary reagents, 1 96-well microtitre plate and 12 single-use 8‑microwell strips

Dynex DS2 (if needed)


Price of cash purchase, supplied on request. A rental price is available but depends on the rental period and number of samples to be processed within this period. Consumables would be needed and purchased separately

Maintenance of the Dynex DS2

Approximately £5,000

Per year, for a fully comprehensive service contract

The manufacturer provides training at no extra cost, typically in the form of 2 days' on-site training. Maintenance costs are only needed for the Dynex DS2 microplate reader. Laboratories with existing microplate readers or automated systems will have maintenance charges as per their existing contracts.

Costs of standard care

Although NICE does not recommend routine therapeutic drug monitoring of infliximab for IBD, specialist commentators advise that infliximab is monitored at a number of centres across the UK. For centres that do not monitor infliximab, standard care costs are assumed to comprise the infliximab drug costs only, without therapeutic drug monitoring.

A 100 mg vial of infliximab costs £419.62 (excluding VAT). The treatment cost varies between people because the dose is adjusted based on individual body weight. Costs may vary in different settings because of negotiated procurement discounts.

One specialist commentator noted that these costs are not representative of current practice, in which cheaper biosimilars such as Remsima and Inflectra are regularly used. RIDASCREEN IFX Monitoring and Anti‑IFX Antibodies tests can both be used with the biosimilar alternatives to infliximab.

Resource consequences

In centres where therapeutic drug monitoring of infliximab is not current practice, the use of RIDASCREEN IFX Monitoring and Anti‑IFX Antibodies tests would represent additional acquisition costs. However, these costs could be offset by savings from drug therapy optimisation and improved disease management.

The per-patient costs of the RIDASCREEN tests are similar to those presented in the NICE diagnostics guidance on therapeutic monitoring of TNF-alpha inhibitors in Crohn's disease. Therefore, for centres that already offer infliximab testing using one of these methods, the RIDASCREEN tests would be unlikely to represent an additional cost.

The economic models described in the NICE diagnostics guidance show that reflex testing strategies are less costly but less effective than standard care. However, the losses reported by the economic model were uncertain because of the difficulties in measuring quality of life in these populations. These results are likely to be generalisable to the RIDASCREEN tests.