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Result of this report
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QuantiFERON-TB Gold (QFT-IGRA) Report Summary
Patient: Ms. Bhagyalakshmi | Age: 44 years | Female
Lab: Dr. Lal PathLabs | Collected: 30/5/2026 | Reported: 2/6/2026
Processed at: LPL National Reference Lab, New Delhi
Test Values
| Parameter | Result | Units |
|---|---|---|
| Gamma Interferon - Antigen tube | 0.15 | IU/mL |
| Gamma Interferon - Nil tube | 0.05 | IU/mL |
| Antigen minus Nil (net value) | 0.10 | IU/mL |
Final Result: NEGATIVE
Interpretation: Mycobacterium tuberculosis infection is UNLIKELY
How to Read This Result
The test works by calculating: Antigen tube - Nil tube = 0.15 - 0.05 = 0.10 IU/mL
According to the lab's reference table:
- A net value < 0.35 IU/mL (with Nil tube ≤ 8.00) = Negative
- This patient's net value of 0.10 is well below the 0.35 threshold, confirming a Negative result
What This Means
- The QFT-IGRA is a blood test that detects the immune system's response to TB bacteria. A Negative result means the patient's white blood cells did not release significant interferon-gamma when exposed to TB antigens - indicating no TB infection is detected.
- This test does not distinguish between latent TB and active TB disease - but a negative result makes both unlikely.
Important Caveats (as stated in the report)
- Immunocompromised patients (HIV, on steroids, etc.) can show false-negative results
- If TB is still clinically suspected, the CDC recommends repeating the test after 8-10 weeks
- A negative result does not completely rule out TB - clinical correlation with symptoms, chest X-ray, and sputum tests is still necessary
- The level of interferon-gamma does NOT indicate the severity or stage of infection
Bottom line: This report is reassuring - the QFT-IGRA test is Negative, meaning TB infection is unlikely. However, the treating doctor at SDM Hospital should correlate this with the patient's clinical picture and any other investigations ordered.
What are the causes of false negative QFT-IGRA results?
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QuantiFERON IGRA false negative causes tuberculosis
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causes false negative QuantiFERON IGRA tuberculosis test clinical
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PMID: 39911267
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I now have comprehensive information from multiple authoritative sources. Here is the complete answer:
Causes of False Negative QFT-IGRA Results
A false negative IGRA means the person IS infected with TB but the test fails to detect it. This happens across three main categories:
1. Host Immune System Factors (Most Common)
These are the most clinically significant causes, as they impair the T-cell interferon-gamma response that the test depends on:
| Condition | Mechanism |
|---|---|
| HIV infection / AIDS | Depletes CD4+ T-cells; pooled OR 6.16 (95% CI 1.36-27.91) for false-negative results |
| Organ transplantation | Immunosuppressive drugs suppress T-cell response |
| TNF-α antagonists (infliximab, etanercept) | Block key cytokine pathway needed for Th1 response |
| Corticosteroids (≥15 mg/day prednisone for ≥1 month) | Broad immunosuppression |
| Chemotherapy / Malignancy | Lymphopenia and immune dysfunction |
| Dialysis / End-stage renal disease (ESRD) | Uremia impairs lymphocyte function; 7x increased false-negative probability |
| Diabetes mellitus | Blunted cell-mediated immunity |
| Malnutrition / Hypoproteinaemia (serum protein <6 g/dL) | Decreased immune response capacity; >7x increased false-negative risk |
| Advanced age (≥65 years) | Immunosenescence - pooled OR 2.06 (95% CI 1.68-2.52) |
| Low peripheral lymphocyte count | Direct cause of reduced IFN-γ production; pooled OR 2.68 (95% CI 2.00-3.61) |
| Sepsis | Systemic immune dysregulation |
| Inflammatory bowel disease | Immune dysregulation + immunosuppressive treatments |
| Pneumoconiosis | Associated impaired immune responses |
Source: Systematic review & meta-analysis, Scientific Reports 2020; Ontario Health Technology Assessment 2024 [PMID 39911267]
2. Timing of Testing (Pre-analytical)
- Recent infection (<8 weeks): After TB exposure, it takes 2-8 weeks for the adaptive immune response to develop sufficiently for detection. Testing during this "window period" gives a false negative.
- CDC recommendation: Repeat testing 8-10 weeks after last known exposure if suspicion remains high.
3. Disease-Specific Factors
- Extra-pulmonary TB - especially miliary TB and TB meningitis - are associated with higher rates of false negatives due to systemic immune suppression from disseminated disease
- Pulmonary TB (paradoxically) - some studies show active pulmonary TB itself can produce false-negative IGRA through T-cell exhaustion or anergy in heavy bacterial load situations
- Smear-negative TB - lower bacterial burden may result in lower immunological stimulation
4. Technical / Pre-analytical Errors
These are laboratory-side causes, as noted by the CDC and University of Iowa Path Handbook:
| Error | Effect |
|---|---|
| Delay in incubation (>16 hours from collection to incubation) | T-cells become non-viable; reduced IFN-γ output |
| Incorrect blood volume in collection tubes | Changes the antigen-to-cell ratio |
| Improper mixing of collection tubes | Inadequate coating of blood on tube walls |
| Cold/improper storage before incubation | T-cell death |
| Incorrect interpretation of results | Human error |
| Heterophile antibodies | Can mask specific IFN-γ responses to ESAT-6/CFP-10 peptides |
5. Summary Table of Risk Categories
| Category | Examples | Strength of Evidence |
|---|---|---|
| HIV / AIDS | CD4 <200 most affected | High (meta-analysis OR 6.16) |
| Low lymphocyte count | Any cause | High (meta-analysis OR 2.68) |
| Advanced age ≥65 | Immunosenescence | High (meta-analysis OR 2.06) |
| ESRD on dialysis | Uremia-induced anergy | Moderate |
| Organ transplant / biologics | TNF-α inhibitors, steroids | Moderate |
| Malnutrition | Serum protein <6 g/dL | Moderate |
| Early infection (<8 weeks) | Window period | Well-established |
| Lab error | Delayed incubation, wrong technique | Well-established |
Clinical Implication
If any of these risk factors apply to a patient AND clinical suspicion for TB remains, a negative IGRA should NOT be used to exclude TB. Options in that scenario include:
- Repeat IGRA after 8-10 weeks (for recent exposures)
- Tuberculin Skin Test (TST) in parallel - combined IGRA + TST sensitivity reaches ~91%
- Proceed to direct microbiological testing (sputum AFB smear/culture, bronchoscopy, lymph node biopsy as appropriate)
- Goldman-Cecil Medicine, p. 3256; CDC IGRA Testing Guidance
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