Quantiferon TB Gold Plus Test at Chughtai Lab

Quantiferon TB Gold Plus/TB-IGRA (Qualitative) at Chughtai Lab

The QuantiFERON-TB Gold Plus (QFT-Plus) is an advanced, modern in vitro diagnostic blood test used to detect cell-mediated immune responses to peptide antigens simulating Mycobacterium tuberculosis proteins. Offered by Chughtai Lab, Pakistan’s premier diagnostic network, this Interferon-Gamma Release Assay (TB-IGRA) represents a major technological leap over the traditional Mantoux Tuberculin Skin Test (TST). The test is highly specific and sensitive, playing a critical role in identifying latent tuberculosis infection (LTBI) and assisting in the diagnostic workup of active tuberculosis. It is a vital tool in public health and clinical medicine, particularly in regions with a high burden of tuberculosis.

Unlike the older skin test, the QuantiFERON-TB Gold Plus is a qualitative blood test that does not require a return visit for reading. It operates by measuring the concentration of interferon-gamma (IFN-γ) released by T-lymphocytes when exposed to specific synthetic peptides representing Mycobacterium tuberculosis antigens. These antigens, namely ESAT-6 and CFP-10, are entirely absent from the Bacillus Calmette-Guérin (BCG) vaccine strain and most non-tuberculous mycobacteria (NTM). Consequently, the test does not produce false-positive results in individuals who have received the BCG vaccine. This makes it an invaluable diagnostic tool in Pakistan, where BCG vaccination is part of the routine national immunization program.

At Chughtai Lab, the test is performed using state-of-the-art automated enzyme-linked immunosorbent assay (ELISA) technology. The assay evaluates the immune response of both CD4+ helper T-cells and CD8+ cytotoxic T-cells. The addition of CD8+ T-cell stimulation in the QuantiFERON-TB Gold Plus version provides a more comprehensive assessment of the cellular immune response. This is particularly useful in individuals with compromised immune systems, recent exposures, or those progressing from latent to active infection, as CD8+ T-cells play a crucial role in the host defense against intracellular pathogens like Mycobacterium tuberculosis.

Clinical Procedure: What to Expect

Understanding the clinical procedure for the QuantiFERON-TB Gold Plus test helps ensure accurate results and minimizes patient anxiety. The process involves precise sample collection, strict handling protocols, and highly controlled laboratory analysis.

Patient Preparation

• No Fasting Required: Patients can eat and drink normally before the blood draw. There are no dietary restrictions associated with this test.
• Medication Disclosure: Inform your physician and the laboratory staff about any immunosuppressive medications, corticosteroids, or chemotherapy you are undergoing, as these can affect your immune response and lead to indeterminate results.
• Vaccination History: If you have recently received a live virus vaccine (such as MMR or varicella), it is recommended to either perform the IGRA test on the same day or wait 4 to 6 weeks, as live vaccines can temporarily suppress cell-mediated immunity.
• Hydration: Ensure you are well-hydrated to facilitate easier venipuncture and smooth blood collection.
• Documentation: Bring your physician’s referral slip and any relevant medical history documents to the Chughtai Lab collection center.

During the Procedure

The procedure begins with standard patient identification and verification of clinical details. A trained phlebotomist at Chughtai Lab will perform a venipuncture, typically drawing blood from a vein in the arm. The blood is collected directly into four specialized QuantiFERON-TB Gold Plus tubes, which must be filled in a specific sequence to ensure accurate testing. These tubes are:

• Nil Tube (Grey Cap): Serves as the negative control, measuring the patient’s baseline interferon-gamma level without antigen stimulation.
• TB1 Tube (Green Cap): Contains peptides designed to stimulate CD4+ T-helper cells.
• TB2 Tube (Yellow Cap): Contains peptides designed to stimulate both CD4+ and CD8+ T-cells, capturing a broader cellular immune response.
• Mitogen Tube (Purple Cap): Serves as the positive control, verifying the patient’s immune competence and ensuring the blood sample contains viable, responsive immune cells.

Each tube must be filled to the marked line (1.0 mL) to maintain the correct blood-to-antigen ratio. Immediately after collection, the tubes are gently shaken to ensure the blood mixes thoroughly with the antigens coated on the tube walls. The samples are then transported to the Chughtai Lab molecular or specialized immunology department under strictly controlled temperature conditions. In the laboratory, the tubes are incubated at 37°C for 16 to 24 hours. Following incubation, the tubes are centrifuged, and the plasma is harvested. The concentration of interferon-gamma in the plasma is measured using an automated ELISA platform. The entire blood collection process takes less than 10 minutes, and patients can resume normal activities immediately.

When is a Quantiferon TB Gold Plus/TB-IGRA Performed?

Screening for Latent Tuberculosis Infection (LTBI)

Latent tuberculosis infection occurs when a person is infected with Mycobacterium tuberculosis but does not have active disease, is asymptomatic, and cannot transmit the bacteria to others. Screening is essential because latent TB can reactivate into active, infectious tuberculosis, particularly if the individual’s immune system becomes compromised. Clinicians request the QuantiFERON-TB Gold Plus test to identify these silent infections, allowing for preventive therapy before active disease develops.

Evaluation of High-Risk Individuals and Healthcare Workers

Healthcare professionals, laboratory staff, and individuals working in correctional facilities or high-density environments are at an increased risk of exposure to tuberculosis. Regular screening using the TB-IGRA test is a standard occupational health protocol. Additionally, individuals who have had close contact with patients diagnosed with active pulmonary tuberculosis are routinely tested to determine if transmission has occurred.

Pre-Immunosuppressive Therapy Screening

Before initiating therapies that suppress the immune system, such as tumor necrosis factor (TNF) inhibitors, biological disease-modifying antirheumatic drugs (DMARDs), systemic corticosteroids, or chemotherapy, patients must be screened for latent TB. Immunosuppression can trigger the rapid reactivation of latent TB into severe, disseminated active disease. The QuantiFERON-TB Gold Plus test provides a reliable pre-treatment screening tool to ensure patient safety.

Investigation of Suspected Active Tuberculosis

While the QFT-Plus test cannot distinguish between latent and active tuberculosis, it is frequently used as an adjunctive diagnostic tool in patients presenting with clinical signs of active TB. When combined with sputum smear microscopy, culture, and molecular tests like GeneXpert, a positive IGRA result supports the diagnosis of tuberculosis, especially in extrapulmonary TB cases where obtaining direct microbiological specimens is challenging.

Differential Diagnosis in BCG-Vaccinated Individuals

In countries like Pakistan, where the BCG vaccine is widely administered, the traditional Tuberculin Skin Test (TST) often yields false-positive results due to cross-reactivity. The QuantiFERON-TB Gold Plus test utilizes specific antigens (ESAT-6 and CFP-10) that do not cross-react with the BCG vaccine. This specificity allows clinicians to accurately differentiate between a true TB infection and a vaccine-induced immune response, preventing unnecessary treatment.

What Does a Quantiferon TB Gold Plus/TB-IGRA Detect?

The QuantiFERON-TB Gold Plus test detects the cell-mediated immune response to Mycobacterium tuberculosis. It measures the concentration of interferon-gamma released by T-cells in response to specific antigens. The test is designed to identify several key immunological parameters and clinical scenarios:

• Baseline Interferon-Gamma Levels: Measured in the Nil tube to identify pre-existing circulating interferon-gamma, which could indicate an active systemic infection or inflammatory state.
• CD4+ T-Cell Activation: Evaluated in the TB1 tube, reflecting the helper T-cell response to TB-specific antigens.
• Combined CD4+ and CD8+ T-Cell Activation: Evaluated in the TB2 tube, capturing the cytotoxic T-cell response, which is particularly active in recent exposures and active disease.
• Immune Competence: Assessed via the Mitogen tube, confirming that the patient’s immune system is capable of producing interferon-gamma.
• Latent Tuberculosis Infection (LTBI): Indicated by a positive result in an asymptomatic patient with normal chest imaging.
• Exposure to Mycobacterium tuberculosis: Confirms that the patient’s immune system has previously encountered and recognized the TB bacilli.
• False-Positive TST Resolution: Clarifies positive skin test results caused by prior BCG vaccination.
• Anergy or Immunosuppression: Identified when a patient has an indeterminate result due to a low Mitogen response, suggesting a compromised immune system.
• In vitro Sample Degradation: Detected when poor sample handling or delayed incubation leads to an indeterminate result.
• Extrapulmonary Tuberculosis Support: Assists in diagnosing TB in non-pulmonary sites (such as bones, joints, or lymph nodes) where direct bacterial detection is difficult.
• Recent TB Transmission: Indicated by a positive result in a close contact of an active TB patient.
• Pediatric TB Screening Support: Provides a highly specific screening option for children over two years of age.
• Pre-transplant Safety Assessment: Screens organ transplant candidates to prevent post-transplant TB reactivation.
• Pre-biological Therapy Baseline: Establishes TB status before starting anti-TNF or other biologic therapies.
• Occupational Health Clearance: Verifies the TB status of healthcare workers and laboratory personnel.
• Millet-like or Disseminated TB Risk: Helps evaluate patients at risk of severe systemic TB.
• Non-Tuberculous Mycobacteria (NTM) Differentiation: Distinguishes TB from most NTM infections, except for M. kansasii, M. szulgai, and M. marinum.
• Immune Recovery Monitoring: Can be used in clinical research to observe changes in immune responses over time.
• Contact Tracing Efficacy: Helps public health officials map the spread of TB in community outbreaks.
• Qualitative Diagnostic Confirmation: Delivers a clear Positive, Negative, or Indeterminate classification to guide clinical decision-making.

Turnaround Time and Report Access at Chughtai Lab

Chughtai Lab is committed to providing accurate and timely diagnostic reports. For the QuantiFERON-TB Gold Plus (TB-IGRA) test, the standard turnaround time is typically 48 to 72 hours from the time of sample collection. This timeline is necessary due to the required 16-to-24-hour incubation period and subsequent ELISA processing. Once the analysis is complete, the report undergoes a rigorous quality control check by qualified clinical pathologists at Chughtai Lab.

Patients are notified via an automated SMS alert as soon as their report is ready. Reports can be accessed online through the official Chughtai Lab website or the Chughtai Lab mobile application. Patients can also collect physical copies of their reports from any Chughtai Lab collection center or opt for home delivery services, ensuring a seamless and convenient diagnostic experience.

Quantiferon TB Gold Plus/TB-IGRA Findings Overview

Structure / Parameter Evaluated	Normal Findings	Possible Abnormal Findings
Nil Control (Negative Control)	Low IFN-γ concentration (≤ 8.0 IU/mL)	High IFN-γ concentration (> 8.0 IU/mL), indicating high background immune activity.
TB1 Antigen (CD4+ Response)	IFN-γ response minus Nil < 0.35 IU/mL	IFN-γ response minus Nil ≥ 0.35 IU/mL, indicating CD4+ T-cell recognition of TB antigens.
TB2 Antigen (CD4+ & CD8+ Response)	IFN-γ response minus Nil < 0.35 IU/mL	IFN-γ response minus Nil ≥ 0.35 IU/mL, indicating CD4+ and CD8+ T-cell recognition of TB antigens.
Mitogen Control (Positive Control)	High IFN-γ response (≥ 0.5 IU/mL), showing normal immune response	Low IFN-γ response (< 0.5 IU/mL), indicating potential anergy, immunosuppression, or sample compromise.
Overall Qualitative Result: Positive	N/A	Indicates infection with Mycobacterium tuberculosis (latent or active).
Overall Qualitative Result: Negative	No detectable immune response to TB antigens; infection unlikely.	N/A
Overall Qualitative Result: Indeterminate	N/A	Inconclusive result due to low Mitogen response or high Nil background; requires retesting.

Note: Diagnostic findings should always be interpreted by a qualified healthcare professional together with the patient’s symptoms, medical history, physical examination, laboratory investigations, previous imaging studies, and other relevant clinical information. Additional investigations or specialist consultation may be recommended depending on the findings.

Why Choose Chughtai Lab for Quantiferon TB Gold Plus/TB-IGRA?

• College of American Pathologists (CAP) Accreditation: Chughtai Lab is accredited by CAP, ensuring the highest international standards of diagnostic quality and accuracy.
• Advanced Automated ELISA Technology: The lab utilizes state-of-the-art automated platforms for processing IGRA tests, minimizing human error and ensuring reproducible results.
• Expert Pathologists and Immunologists: Reports are reviewed and signed off by highly qualified consultant pathologists specializing in immunology and molecular diagnostics.
• Convenient Home Sample Collection: Patients can schedule a home sample collection, allowing a trained phlebotomist to collect the blood sample in the comfort of their home.
• Nationwide Network of Centers: With hundreds of collection centers across Pakistan, Chughtai Lab offers unmatched accessibility.
• Secure Online Report Access: Patients and referring physicians can easily view, download, and print diagnostic reports via the secure online portal and mobile app.
• Strict Quality Control Protocols: The laboratory adheres to rigorous internal and external quality control measures to maintain diagnostic integrity.
• Patient-Centric Care: Chughtai Lab is dedicated to providing a compassionate, comfortable, and professional environment for all patients during the diagnostic process.