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    Clinical Trial Results:
    Treatment of Latent Tuberculosis Infection: Diagnostics (RID-TB:Dx) A randomised controlled trial to evaluate a RD-1 based C-Tb skin test diagnostic strategy for detection of latent TB infection and initiation of TB preventive treatment in the UK

    Summary
    EudraCT number
    		 2019-002592-34
    Trial protocol
    		 GB  
    Global end of trial date
    12 Mar 2025

    Results information
    Results version number
    		 v1(current)
    This version publication date
    25 Dec 2025
    First version publication date
    25 Dec 2025
    Other versions

    Trial information

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    Trial identification
    Sponsor protocol code
    RID-TB:Dx
    Additional study identifiers
    ISRCTN number
    		 ISRCTN17936038
    US NCT number
    		 -
    WHO universal trial number (UTN)
    		 -
    Sponsors
    Sponsor organisation name
    University College London
    Sponsor organisation address
    90 High Holborn, London, United Kingdom, WC1V 6LJ
    Public contact
    Trinh Duong, Institute of Clinical Trials and Methodology at UCL, t.duong@ucl.ac.uk
    Scientific contact
    Trinh Duong, Institute of Clinical Trials and Methodology at UCL, t.duong@ucl.ac.uk
    Paediatric regulatory details
    Is trial part of an agreed paediatric investigation plan (PIP)
    No
    Does article 45 of REGULATION (EC) No 1901/2006 apply to this trial?
    No
    Does article 46 of REGULATION (EC) No 1901/2006 apply to this trial?
    No
    Results analysis stage
    Analysis stage
    Final
    Date of interim/final analysis
    12 Mar 2025
    Is this the analysis of the primary completion data?
    Yes
    Primary completion date
    12 Mar 2025
    Global end of trial reached?
    Yes
    Global end of trial date
    12 Mar 2025
    Was the trial ended prematurely?
    Yes
    General information about the trial
    Main objective of the trial
    The overall aim was to evaluate patient-related outcomes for C-Tb testing for latent TB infection (LTBI) screening and process of implementation within the NHS. The primary objective of the trial was to estimate the proportion of participants offered C-Tb skin test diagnostic strategy who initiate treatment for LTBI within 12 weeks.
    Protection of trial subjects
    The study engaged people with a high risk of LTBI, including new entrants to the UK as well as individuals who are contacts of people with active TB. This population is potentially marginalised, vulnerable or hard-to-engage in care. Engagement were carried out in such a way that stigma would be minimised, and participants were not disadvantaged in any way. Our PPI partner, TB Alert, has a long history working with the populations that we recruited from, and provided advice for our patient-facing interactions.
    Background therapy
    		 IGRA tests for LTBI: T-SPOT, QuantiFERON Gold
    Evidence for comparator
    		 The new C-Tb skin test was developed by Statens Serum Institut (SSI), and reported to have high overall concordance (94%), and similar sensitivity (74%) and specificity (96%) to the QFT-Gold In Tube blood IGRA test. C-Tb contains recombinant ESAT-6 (dimer) and CFP10 (monomer) antigens derived from Mycobacterium tuberculosis (M.tb). Similar to the QFT-Gold In Tube, and in contrast to the TST, C-Tb appears unaffected by previous BCG vaccination and HIV infection. Amongst healthy volunteers, contacts of TB cases, and people with current/previous TB disease, C-Tb shows higher rates of positivity with increasing levels of exposure to M.tb. C-Tb could thus be an immunological improvement on the standard TST, and could offer an accurate, acceptable and cheaper replacement or alternative to the IGRA. Following a systematic review that confirmed the similar accuracy of C-Tb to IGRA, the World Health Organization recommended the use of C-Tb as an alternative to existing tests. However, there is no evidence of the impact of C-Tb testing on patient and process outcomes when used in routine practice.
    Actual start date of recruitment
    15 Oct 2021
    Long term follow-up planned
    No
    Independent data monitoring committee (IDMC) involvement?
    Yes
    Population of trial subjects
    Number of subjects enrolled per country
    Country: Number of subjects enrolled
    United Kingdom: 126
    Worldwide total number of subjects
    126
    EEA total number of subjects
    0
    Number of subjects enrolled per age group
    In utero
    0
    Preterm newborn - gestational age < 37 wk
    0
    Newborns (0-27 days)
    0
    Infants and toddlers (28 days-23 months)
    0
    Children (2-11 years)
    0
    Adolescents (12-17 years)
    4
    Adults (18-64 years)
    122
    From 65 to 84 years
    0
    85 years and over
    0

    Subject disposition

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    Recruitment
    Recruitment details
    		 Participants were recruited from the UK between October 2021 to September 2024. We approached 9 primary care sites, 11 secondary care sites, and one community site for set-up. However, only one primary care site and five secondary care sites agreed to participate and recruited at least one participant.

    Pre-assignment
    Screening details
    		 Participant Inclusion Criteria 1. Aged 16 – 65 years 2. Eligible for LTBI testing with IGRA and treatment for LTBI according to UK guidance 3. Willing and able to provide written informed consent 4. Willing and able to comply with the trial Participant Exclusion Criteria 1. Displaying any symptoms or signs of active TB disease*

    Pre-assignment period milestones
    Number of subjects started
    		 353 [1]
    Number of subjects completed
    		 126

    Pre-assignment subject non-completion reasons
    Reason: Number of subjects
    		 Not eligible: 38
    Reason: Number of subjects
    		 Declined to participate: 189
    Notes
    [1] - The number of subjects reported to have started the pre-assignment period are not the same as the worldwide number enrolled in the trial. It is expected that these numbers will be the same.
    Justification: Pre-assignment figure of 353 included participants screened for enrolment, or these 126 were enrolled.
    Period 1
    Period 1 title
    Main Trial (overall period)
    Is this the baseline period?
    		 Yes
    Allocation method
    Randomised - controlled
    Blinding used
    		 Not blinded

    Arms
    Are arms mutually exclusive
    Yes

    Arm title
    		 Intervention arm
    Arm description
    		 C-Tb diagnostic strategy
    Arm type
    		 Experimental

    Investigational medicinal product name
    C-Tb
    Investigational medicinal product code
    C-Tb
    Other name
    Cy-Tb
    Pharmaceutical forms
    Solution for injection/infusion
    Routes of administration
    Intradermal use
    Dosage and administration details
    0.1ml total administered once

    Arm title
    		 Control arm
    Arm description
    		 IGRA diagnostic strategy
    Arm type
    		 Standard of care comparator

    Investigational medicinal product name
    No investigational medicinal product assigned in this arm
    Number of subjects in period 1
    		Intervention arm Control arm
    Started
    76
    50
    Completed
    65
    41
    Not completed
    11
    9
         participant discharged from TB clinic
    1
    -
         Lost to follow-up
    10
    9

    Baseline characteristics

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    Baseline characteristics reporting groups
    Reporting group title
    Intervention arm
    Reporting group description
    		 C-Tb diagnostic strategy

    Reporting group title
    Control arm
    Reporting group description
    		 IGRA diagnostic strategy

    Reporting group values
    		 Intervention arm Control arm Total
    Number of subjects
    		 76 50 126
    Age categorical
    Units: Subjects
        In utero
    		 0 0 0
        Preterm newborn infants (gestational age < 37 wks)
    		 0 0 0
        Newborns (0-27 days)
    		 0 0 0
        Infants and toddlers (28 days-23 months)
    		 0 0 0
        Children (2-11 years)
    		 0 0 0
        Adolescents (12-17 years)
    		 2 2 4
        Adults (18-64 years)
    		 74 48 122
        From 65-84 years
    		 0 0 0
        85 years and over
    		 0 0 0
    Age continuous
    Units: years
        median (inter-quartile range (Q1-Q3))
    		 27 (24 to 32) 27 (23 to 31) -
    Gender categorical
    Units: Subjects
        Female
    		 31 20 51
        Male
    		 45 30 75
    TB risk exposure group
    Units: Subjects
        High TB burden country
    		 57 34 91
        Close contact
    		 18 14 32
        Healthcare worker
    		 1 1 2
        Other
    		 0 1 1
    Site
    Units: Subjects
        Newham Transitional
    		 38 24 62
        Royal Free
    		 3 3 6
        Whittington
    		 24 14 38
        North Middlesex University Hospital
    		 1 0 1
        Newham Chest Clinic
    		 9 8 17
        Mile End
    		 1 1 2
    Current Employment Status
    Units: Subjects
        Full-time employment
    		 24 16 40
        Part-time employment
    		 17 8 25
        Student
    		 18 15 33
        Retired/unemployed/unable to work
    		 17 11 28
    BCG Vaccination status
    Units: Subjects
        Vaccinated
    		 52 34 86
        Unvaccinated
    		 13 9 22
        Unknown
    		 11 7 18
    Country of birth
    Units: Subjects
        UK
    		 8 9 17
        India
    		 40 22 62
        Bangladesh
    		 7 7 14
        Abroad
    		 21 12 33

    End points

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    End points reporting groups
    Reporting group title
    Intervention arm
    Reporting group description
    		 C-Tb diagnostic strategy

    Reporting group title
    Control arm
    Reporting group description
    		 IGRA diagnostic strategy

    Subject analysis set title
    Modified Intention to Treat
    Subject analysis set type
    		 Modified intention-to-treat
    Subject analysis set description
    Modified intention to treat population excluded one participant who was not properly randomised.

    Primary: LTBI Treatment initiation - Primary analysis

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    End point title
    		 LTBI Treatment initiation - Primary analysis
    End point description
    Number of participants initiating LTBI treatment within 12 weeks (mITT population)
    End point type
    Primary
    End point timeframe
    Within 12 weeks after LTBI testing
    End point values
    		 Intervention arm Control arm Modified Intention to Treat
    Number of subjects analysed
    76
    49
    125
    Units: People
        Reached endpoint
    3
    0
    3
        Did not reach endpoint
    73
    49
    122
    Statistical analysis title
    		 Proportion of participants initiating treatment
    Statistical analysis description
    The primary objective of the study is to estimate the proportion of participants offered C-Tb testing who initiate treatment for LTBI within 12 weeks (the study was not powered for a comparison between arms). The analysis population was modified intention-to-treat.
    Comparison groups
    Intervention arm v Control arm
    Number of subjects included in analysis
    125
    Analysis specification
    Pre-specified
    Analysis type
    		 other [1]
    Method
    Parameter type
    		 Proportion
    Point estimate
    0.0395
    Confidence interval
         level
    		 95%
         sides
    2-sided
         lower limit
    		 0.0135
         upper limit
    		 0.1097
    Notes
    [1] - The primary objective of the study is to estimate the proportion of participants offered C-Tb testing who initiate treatment for LTBI within 12 weeks (the study was not powered for a comparison between arms)

    Adverse events

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    Adverse events information
    Timeframe for reporting adverse events
    During study follow-up up to 4 weeks after LTBI test administration
    Adverse event reporting additional description
    All participants receiving LTBI testing were included in safety analyses (n=126). Active TB disease was not included as an adverse event (NB. One participant in intervention arm was a late screening failure with TB diagnosed soon after randomisation).
    Assessment type
    		 Systematic
    Dictionary used for adverse event reporting
    Dictionary name
    		 MedDRA
    Dictionary version
    25.1
    Reporting groups
    Reporting group title
    Intervention arm
    Reporting group description
    		 C-Tb diagnostic strategy - before study redesign all participants randomised to C-Tb were administered C-Tb (n=15) after the study redesign participants randomised (n=76) to the C-Tb intervention arm could elect not to have it and instead choose to have the standard of care IGRA blood test. 10 participants randomised to the intervention arm chose to have the C-Tb test

    Reporting group title
    Control arm
    Reporting group description
    		 IGRA diagnostic strategy

    Serious adverse events
    		 Intervention arm Control arm
    Total subjects affected by serious adverse events
         subjects affected / exposed
    0 / 76 (0.00%)
    0 / 50 (0.00%)
         number of deaths (all causes)
    0
    0
         number of deaths resulting from adverse events
    0
    0
    Frequency threshold for reporting non-serious adverse events: 0%
    Non-serious adverse events
    		 Intervention arm Control arm
    Total subjects affected by non serious adverse events
         subjects affected / exposed
    2 / 76 (2.63%)
    2 / 50 (4.00%)
    Injury, poisoning and procedural complications
    Contusion
    Additional description: Bruising at site of C-Tb injection. Grade 1 - mild.
         subjects affected / exposed
    1 / 76 (1.32%)
    0 / 50 (0.00%)
         occurrences all number
    1
    0
    Dog bite
         subjects affected / exposed
    0 / 76 (0.00%)
    1 / 50 (2.00%)
         occurrences all number
    0
    1
    Nervous system disorders
    Headache
    Additional description: Grade 1 - mild
         subjects affected / exposed
    1 / 76 (1.32%)
    0 / 50 (0.00%)
         occurrences all number
    1
    0
    General disorders and administration site conditions
    Influenza like illness
    Additional description: Grade 1 - mild
         subjects affected / exposed
    1 / 76 (1.32%)
    0 / 50 (0.00%)
         occurrences all number
    1
    0
    Blood and lymphatic system disorders
    Lymphadenopathy
         subjects affected / exposed
    0 / 76 (0.00%)
    1 / 50 (2.00%)
         occurrences all number
    0
    1
    Skin and subcutaneous tissue disorders
    Erythema
    Additional description: Grade 1 - Mild
         subjects affected / exposed
    1 / 76 (1.32%)
    0 / 50 (0.00%)
         occurrences all number
    1
    0

    More information

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    Substantial protocol amendments (globally)
    Were there any global substantial amendments to the protocol? Yes
    Date
    Amendment
    07 Dec 2022
    Full protocol redesign

    Interruptions (globally)
    Were there any global interruptions to the trial? No

    Limitations and caveats
    Limitations of the trial such as small numbers of subjects analysed or technical problems leading to unreliable data.
    The trial was stopped early due to low recruitment rates, with only 126 of the target n=400 enrolled
    For support, Contact us.
    The status and protocol content of GB trials is no longer updated since 1 January 2021. For the UK, as of 31 January 2021, EU Law applies only to the territory of Northern Ireland (NI) to the extent foreseen in the Protocol on Ireland/NI. Legal notice
    As of 31 January 2023, all EU/EEA initial clinical trial applications must be submitted through CTIS . Updated EudraCT trials information and information on PIP/Art 46 trials conducted exclusively in third countries continues to be submitted through EudraCT and published on this website.

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