Authorized QIAGEN Distributor in Nepal · JHS Analytic Traders
QuantiFERON TB Gold Plus Kit.
The WHO-endorsed interferon-gamma release assay (IGRA) for latent tuberculosis detection. A single blood draw. An objective result. Unaffected by BCG vaccination.
QuantiFERON-TB Gold Plus (QFT-Plus) is QIAGEN's fourth-generation interferon-gamma release assay (IGRA) — the WHO-endorsed, FDA-cleared, CE-IVD blood test for detecting latent tuberculosis infection (LTBI). It is the modern, single-visit replacement for the tuberculin skin test (Mantoux/PPD), and WHO recognises IGRA as a valid alternative to TST for LTBI diagnosis — with a practical specificity advantage in BCG-vaccinated populations such as Nepal, where TST cross-reactivity confounds results.
The test works by exposing a patient's whole blood to TB-specific peptide antigens — ESAT-6 and CFP-10 — in four colour-coded collection tubes. Sensitised T-cells from anyone with prior Mycobacterium tuberculosis exposure release interferon-gamma (IFN-γ) into the plasma, which is then quantified by ELISA against a calibrated standard curve. The result is an objective measurement in IU/mL, not a subjective skin reading — eliminating the reader variability and two-visit logistics that have limited TST programmes across South Asia for decades.
What sets QFT-Plus apart from third-generation IGRA is the TB2 tube's CD8+ T-cell stimulation — a capability unique to QIAGEN's 2015-onward platform. CD8+ cytotoxic T-cells are particularly relevant in active and recent TB exposure, in HIV co-infection, and in immunocompromised patients where CD4+-only assays under-detect. For Nepal's healthcare workers, hostel and prison populations, paediatric BCG-vaccinated cohorts, immigration medicals, and patients on biologics or pre-transplant workup, QFT-Plus delivers diagnostic accuracy that PPD simply cannot match.
JHS Analytic Traders is the authorized QIAGEN distributor in Nepal for QuantiFERON-TB Gold Plus, supplying the kit across Kathmandu, Pokhara, Biratnagar, and the rest of the country — alongside ELISA readers, washers, incubators, and the broader laboratory infrastructure required to run an IGRA workflow. We don't just sell the kit. We deliver the workflow, with manufacturer-backed product authenticity and supply continuity.
The Four QFT-Plus Collection Tubes.
Every QuantiFERON-TB Gold Plus test in Nepal uses four colour-coded blood collection tubes — each pre-loaded with specific antigens or controls. Together they enable the most accurate detection of latent Mycobacterium tuberculosis infection available, with both CD4+ and CD8+ T-cell stimulation unique to this fourth-generation IGRA.
Baseline control with no TB antigens — measures background interferon-gamma levels.
Background IFN-γ Control
ESAT-6 and CFP-10 peptides — TB-specific antigens absent from the BCG vaccine.
CD4+ T-Cell Response
Extended peptide panel — broader immune response detection unique to QFT-Plus.
CD4+ & CD8+ Response
Positive control that validates immune responsiveness — guards against indeterminate results.
Immune Validity Controlper patient
at 37 °C ± 1 °C
cut-off (above Nil)
· 24 h turnaround
From Blood Draw to Result
Blood Collection
Draw 1 mL into each of the 4 QFT-Plus tubes. Shake each tube 10 times to mix antigens with blood.
Incubation
Incubate upright at 37°C ± 1°C for 16–24 hours. TB antigens contact and stimulate T-cells in the blood.
IFN-γ Release
TB-sensitised T-cells (CD4+ and CD8+) secrete interferon-gamma into the plasma if prior TB exposure occurred.
ELISA Detection
Plasma is harvested and IFN-γ concentration is measured by enzyme-linked immunosorbent assay (ELISA).
Result
Positive (≥ 0.35 IU/mL above Nil), Negative, or Indeterminate. Reported within 24 hours of collection.
IGRA vs. Tuberculin Skin Test (TST)
| QFT-Plus (IGRA) | TST (Mantoux) | |
|---|---|---|
| Patient visits required | ✓ One visit only | Two visits (48–72 hrs apart) |
| Affected by BCG vaccination | ✓ Not affected | ✗ False positives common |
| Result objectivity | ✓ Objective IU/mL value | Subjective mm reading |
| Turnaround time | ✓ 24 hours | 48–72 hours |
| WHO recommendation | ✓ Valid alternative; specificity unaffected by BCG | Valid, but cross-reacts with BCG vaccination |
| Reader variability | ✓ None (lab instrument) | High (clinician-dependent) |
| Boosting effect on repeat testing | ✓ None | ✗ Can boost subsequent TST results |
QuantiFERON TB Gold Plus — Official QIAGEN Overview
Key Parameters
| Assay Type | Interferon-Gamma Release Assay (IGRA) — ELISA-based |
| Generation | Fourth generation (QFT-Plus) — includes CD8+ T-cell stimulation tube (TB2) |
| Sample Type | Whole blood — 1 mL per tube, 4 tubes per patient (4 mL total) |
| Collection Tubes | Nil (grey), TB1 (green, CD4+), TB2 (yellow, CD4+ & CD8+), Mitogen (purple, positive control) |
| Pack Format | Sold as two components: Blood Collection Tube Set (single-patient, 4 tubes) + ELISA Kit (2-plate, 96-well format — approximately 44 patient samples per 2-plate kit) |
| Incubation | 16–24 hours at 37°C ± 1°C, upright (non-CO₂ incubator) |
| Readout | ELISA — IFN-γ measured in IU/mL via 450 nm absorbance (with 620–650 nm reference) |
| Positive Threshold | ≥ 0.35 IU/mL and ≥ 25% above Nil value |
| Throughput per Plate | Up to 22 patient samples per 96-well ELISA plate (4 tubes × 22 + 8 wells for standards in duplicate) |
| Reported Performance | Sensitivity ~94%, specificity ~97% per QIAGEN FDA PMA data; pooled meta-analysis: sensitivity 91.4%, specificity 97.8% (Oh et al., Clin Infect Dis, 2020) |
| Tube Storage (empty) | 4–25°C — refrigeration not required for empty tubes |
| Tube Handling (after draw) | Hold at 17–25°C and incubate within 16 hours of collection — do not refrigerate filled tubes before incubation |
| ELISA Kit Storage | 2–8°C (refrigerated) |
| Sample Stability (pre-incubation) | Up to 16 hours at 17–25°C after blood collection |
| Result Software | QuantiFERON Analysis Software (free download from QIAGEN) — applies cut-off logic and generates patient reports |
| Regulatory | CE-IVD marked; FDA-cleared; WHO-endorsed for LTBI diagnosis |
| Manufacturer | QIAGEN GmbH, Germany — ISO 13485 certified |
Where QFT-Plus Is Used
Healthcare Worker Screening
Annual TB screening of hospital and clinical staff across Nepal — where BCG vaccination makes TST unreliable for routine monitoring.
Pre-Employment & Institutional
TB clearance for staff in hospitals, research facilities, food processing, and government institutions.
Immigration & Travel Health
Accepted IGRA for visa and immigration medical examinations requiring TB clearance documentation.
HIV & Immunocompromised Patients
Screening HIV-positive patients and those on immunosuppressive therapy before initiating treatment — where TST is particularly unreliable.
Lab Infrastructure for Running QFT-Plus
QFT-Plus is an ELISA-based IGRA — meaning the kit itself is consumable and the lab needs the standard ELISA workflow infrastructure. Listed below is the equipment QIAGEN's instructions for use specify as required to run the assay. JHS supplies the full chain.
37°C Incubator (non-CO₂)
For the 16–24 hour blood incubation step. Standard dry incubator; CO₂ environment is not required.
Microplate ELISA Reader
Capable of 450 nm absorbance with 620–650 nm reference filter. Standard ELISA reader compatible with QuantiFERON Analysis Software output.
Microplate Washer
For automated washing of the 96-well ELISA plate between binding, conjugate, and substrate steps.
Centrifuge
To harvest plasma from the incubated tubes. QIAGEN protocol: 2000–3000 × g for 5–15 minutes.
Calibrated Pipettes
Variable-volume single-channel and 8-channel multichannel pipettes for plate setup, standards, and reagent dispensing.
QuantiFERON Analysis Software
Free software from QIAGEN that imports raw ELISA data, applies cut-off logic, and generates patient-ready reports.
QFT-Plus vs. T-SPOT.TB
The two WHO-endorsed IGRA platforms for latent TB diagnosis are QIAGEN's QuantiFERON-TB Gold Plus and Oxford Immunotec's T-SPOT.TB. Both are validated alternatives to TST; they differ in workflow and operational profile.
| QFT-Plus | T-SPOT.TB | |
|---|---|---|
| Detection method | ELISA — IFN-γ in plasma (IU/mL) | ELISPOT — counts IFN-γ-secreting T-cells (spot-forming units) |
| Sample preparation | Whole blood directly into collection tubes | PBMC isolation required before assay |
| Hands-on complexity | Lower — direct whole-blood workflow | Higher — additional cell separation step |
| CD8+ T-cell stimulation | ✓ Included (TB2 tube) | Not specifically included |
| Equipment overlap | Standard ELISA reader and washer | Requires ELISPOT reader (specialised) |
| Manufacturer | QIAGEN (Germany) | Oxford Immunotec / Revvity (UK) |
QFT-Plus Is One Part of What We Can Build for Your Lab.
JHS Analytic Traders sources diagnostic and laboratory equipment from over 20 global manufacturers. If your requirements go beyond a single kit — alternative IGRA platforms, TB culture systems, broader infectious disease panels, or a complete diagnostic workflow — we adapt to what your lab actually needs.
Tell us your clinical context, throughput, and budget. We'll configure the right solution.
What is QuantiFERON-TB Gold Plus?
QFT-Plus is QIAGEN's fourth-generation IGRA blood test for detecting latent tuberculosis infection. It measures the immune system's response to TB-specific antigens (ESAT-6 and CFP-10) through an ELISA. A result is available within 24 hours of blood collection, from a single patient visit.
Why is QFT-Plus preferred over TST in Nepal?
Nepal has near-universal BCG vaccination at birth. The tuberculin skin test gives false positives in BCG-vaccinated individuals, making it unreliable for LTBI screening. QFT-Plus uses antigens not present in the BCG vaccine strain, so results are accurate regardless of BCG vaccination history. WHO recognises IGRA as a valid alternative to TST, with a specificity advantage in BCG-vaccinated populations where TST cross-reactivity is a concern.
What are the four QFT-Plus collection tubes?
Each patient requires four tubes: Nil (baseline control, no antigen), TB1 (ESAT-6 + CFP-10 targeting CD4+ T-cells), TB2 (extended peptide panel targeting CD4+ and CD8+ T-cells — unique to the Plus generation), and Mitogen (positive control confirming immune responsiveness).
How is the result interpreted?
After ELISA, the IFN-γ concentration in each tube is compared. A result is Positive (≥ 0.35 IU/mL and ≥ 25% above Nil), Negative, or Indeterminate (when the Mitogen control fails or the Nil value is very high). Indeterminate results require retesting.
Does JHS supply only QIAGEN QuantiFERON?
No. QFT-Plus is one diagnostic solution within JHS Analytic Traders' broader TB and infectious disease portfolio. We source equipment and kits from multiple global manufacturers and can configure a complete diagnostic workflow matched to your lab's volume, budget, and accreditation requirements. Contact us to discuss your full requirement.
Need a complete TB diagnostic workflow?
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