An indeterminate result of QuantiFERON-TB Gold In-Tube for miliary tuberculosis due to a high level of IFN-γ production

CD69 flow cytometry to complement interferon-γ release assay for active tuberculosis

BACKGROUND

The interferon-γ (IFN-γ) release assay (IGRA) is widely used to diagnose tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb). However, indeterminate IGRA results due to "high Nil" or "low PHA" responses limit its clinical utility. We developed a novel assay using CD69 flow cytometry (FC) to complement IGRA.

METHODS

CD69 FC measures the surface CD69 expression on T cells prior to centrifugation to harvest the plasma for IGRA. T cell responses against Mtb antigen 1 (Ag1) or Ag2 were measured using three-color FC (CD3, CD4, and CD69) in TB (n = 140) and non-TB groups (n = 117). The cutoff values of Δ%CD69^bright cells (stimulated minus unstimulated) for CD4⁺ and CD4^- T cells were established based on healthy individuals (n = 63). The assay performances of CD69 FC and IGRA were compared.

RESULTS

In subjects with determinate IGRA results ("positive" or "negative"; n = 216), the diagnostic accuracies of CD69 FC (90.3%) and IGRA (87.0%) were not significantly different (p = 0.31). For indeterminate IGRA results (n = 40), CD69 FC attained a diagnostic accuracy of 92.5%. The CD4⁺ /CD4^- ratio within CD69^bright T cells measured by CD69 FC was significantly higher (p < 0.05) in the active TB group (6.39 ± 132.05; n = 72) than in other CD69 FC-positive subjects (2.84 ± 15.36; n = 63) (p < 0.05), whereas CD8 responses expected by IGRA (difference of IFN-γ levels between Mtb Ag tubes) did not differ significantly (0.00 ± 9.18 and 0.00 ± 4.25, respectively, IU/ml; p = 0.58).

CONCLUSIONS

We demonstrated the potential of CD69 FC as a simple, rapid assay for clarifying indeterminate IGRA results and identifying active TB. With further improvements, CD69 FC may complement the IGRA to enhance TB risk stratification in the routine diagnostic workup.

Tuberculosis Infection in Children and Adolescents: Testing and Treatment

Tuberculosis (TB) remains an important problem among children in the United States and throughout the world. There is no diagnostic reference standard for latent tuberculosis infection (also referred to as tuberculosis infection [TBI]). The tuberculin skin test (TST) has many limitations, including difficulty in administration and interpretation, the need for a return visit by the patient, and false-positive results caused by cross-reaction with Mycobacterium bovis-bacille Calmette-Guerin vaccines and many nontuberculous mycobacteria. Interferon-gamma release assays (IGRAs) are blood tests that use antigens specific for M tuberculosis; as a result, IGRAs yield fewer false-positive results than the TST. Both IGRAs and the TST have reduced sensitivity in immunocompromised children, including children with severe TB disease. Both methods have high positive predictive value when applied to children with risk factors for TBI, especially recent contact with a person who has TB disease. The advantages of using IGRAs and diminished experience with the placement and interpretation of the TST favor expanded use of IGRAs in children in the United States. There are now several effective and safe regimens for the treatment of TBI in children. For improved adherence to therapy, the 3 rifamycin-based regimens are preferred because of their short duration. Daily isoniazid can be used if there is intolerance or drug interactions with rifamycins. A TB specialist should be involved when there are questions regarding testing interpretation, selection of an appropriate treatment regimen, or management of adverse effects.

Features of indeterminate results of QuantiFERON-TB Gold In-Tube test in patients with haematological malignancies

Background and aims

The application of QuantiFERON-TB Gold in-Tube (QFT-GIT) in patients with haematological malignancies (HMs) has not been well studied. Therefore, we aimed to investigate the features of patients with HMs whose QFT-GIT results were indeterminate.

Methods

This study enrolled patients with HMs for the analysis of QFT-GIT tests and additional 2-year follow-up. The characteristics and predictors of QFT-GIT indeterminate results were identified. Mycobacterium tuberculosis (TB) incidence rate (IR) and incidence rate ratio (IRR) were also investigated.

Results

Of 89 participants, 27 (30.3%) had QFT-GIT indeterminate results. The QFT-GIT indeterminate patients were characterized with the diagnosis of leukaemia (63.0% versus 32.3%, p = 0.044), abnormal white blood count (WBC) (88.9% versus 14.5%, p = 0.001), abnormal lymphocyte percentage (81.5% versus 14.5%, p = 0.001) and lower lymphocyte count (×10⁹/l) (0.5 versus 2.2, p = 0.000) when compared with those with determinate results. Meanwhile, abnormal WBC [odds ratios (OR): 15.18, p = 0.003] and lymphocyte percentage (OR: 6.90, p = 0.033) were predictors of indeterminate results. One patient with the QFT-GIT indeterminate status and high interferon-γ level of negative control result developed active TB with a TB IR of 18.5 per 1000 person-years and an IRR of 0.1 (95% confidence interval, 0.01-0.71) when compared with positive QFT-GIT patients without prophylaxis treatment.

Conclusion

Abnormal ranges of WBC and lymphocyte differential count percentage were independent predictors useful to determine the optimal timing of implementing QFT-GIT test in patients with HMs.

Alternative Quantiferon cytokines for diagnosis of children with active tuberculosis and HIV co-infection in Ghana

IFN-γ release assays (IGRAs) often present false-negative or indeterminate results in children with tuberculosis. HIV co-infection may contribute to decreased sensitivity of IGRAs by impairing T-cell IFN-γ expression. Measurement of alternative cytokines in QuantiFERON^® (QFT) supernatants can circumvent the IFN-γ-dependency and may improve QFT sensitivity. We aimed to identify additional cytokines from QFT supernatants for detection of Mycobacterium tuberculosis infection in children with tuberculosis and HIV co-infection from Ghana. Concentrations of 18 cytokines in QFT supernatants from children (0-16 years) with tuberculosis concomitantly infected with HIV (n = 25) or without HIV (n = 24) from Ghana were measured using cytometric bead array (CBA). 29% of the children showed positive IFN-γ test results, and five cytokines, i.e., IL-6, IL-21, TNF-α, IL-1α and IP-10, detected M. tuberculosis infection with comparable or, for IL-6, with significantly higher sensitivity (59%). Increased age and HIV co-infection were associated with decreased cytokine induction, and especially IL-21 and IP-10 were less prevalent in HIV co-infected children with tuberculosis. Combined cytokine analyses increased proportions of positive tests, and a four-cytokine subset (i.e., IL-6, IL-21, IFN-γ, IL-1α) predicted 78% of the children with tuberculosis correctly. Combined evaluation of IFN-γ and alternative cytokines improved IGRA-sensitivity in children with tuberculosis.

IFN-γ Release Assay Result Is Associated with Disease Site and Death in Active Tuberculosis

RATIONALE

The IFN-γ release assays and tuberculin skin tests are used to support the diagnosis of both latent and active tuberculosis. However, we previously demonstrated that a negative tuberculin test in active tuberculosis is associated with disseminated disease and death. It is unknown whether the same associations exist for IFN-γ release assays.

OBJECTIVES

To determine the association between these tests and site of tuberculosis and death among persons with active tuberculosis.

METHODS

We analyzed IFN-γ release assays and tuberculin test results for all persons with culture-confirmed tuberculosis reported to the U.S. National Tuberculosis Surveillance System from 2010 to 2014. We used logistic regression to calculate the association between these tests and site of disease and death.

MEASUREMENTS AND MAIN RESULTS

A total of 24,803 persons with culture-confirmed tuberculosis had either of these test results available for analysis. Persons with a positive tuberculin test had lower odds of disseminated disease (i.e., miliary or combined pulmonary and extrapulmonary disease), but there was no difference in the odds of disseminated disease with a positive IFN-γ release assay. However, persons who were positive to either of these tests had lower odds of death. An indeterminate IFN-γ release assay result was associated with greater odds of both disseminated disease and death.

CONCLUSIONS

Despite perceived equivalence in clinical practice, IFN-γ release assays and tuberculin test results have different associations with tuberculosis site, yet similar associations with the risk of death. Furthermore, an indeterminate IFN-γ release assay result in a person with active tuberculosis is not unimportant, and rather carries greater odds of disseminated disease and death. Prospective study may improve our understanding of the underlying mechanisms by which these tests are associated with disease localization and death.