Repeatability of QuantiFERON-TB gold in-tube assay results near cut-off points

Association between vitamin D and insulin resistance in adults with latent tuberculosis infection: Results from the National Health and Nutrition Examination Survey (NHANES) 2011-2012

BACKGROUND

Evidence demonstrated that vitamin D insufficiency was involved in insulin resistance (IR) pathogenesis and associated with tuberculosis. However, the association of vitamin D and IR in patients with latent tuberculosis infection (LTBI) remains unclear. This study aims to evaluate the association between vitamin D and insulin resistance in US adults with LTBI.

METHOD

National Health and Nutrition Examination Survey (NHANES) participants ≥ 20 years during the years 2011-2012 with positive QuantiFERON®-TB Gold-In-Tube (QFT) or tuberculin skin testing (TST) were enrolled in present study. Participants with LTBI were divided into 2 groups: (1) vitamin D insufficiency group (n = 267), and (2) vitamin D sufficiency group (n = 437).

RESULTS

Weighted analysis of all the population in the study showed that serum 25(OH)D inversely correlated with HOMA-IR (r = -0.14, P = 0.008). The vitamin D insufficiency group had higher fasting insulin (17.5 (1.38) vs. 15.29 (3.1), respectively, P = 0.0013) and HOMA-IR (5.0 (0.4) vs. 4.5 (1), respectively, P = 0.013) than the vitamin D sufficiency group. In adjusted analysis, vitamin D levels was independently associated with insulin resistance (adjusted OR [aOR] 2.74; 95% CI, 1.01-7.48, p = 0.0489).

CONCLUSIONS

Taken together, our study suggested that serum 25(OH) D concentrations were inversely and independently associated with HOMA-IR in LTBI.

The use of a borderline zone for the interpretation of interferon-gamma release assay results for serial screening of healthcare workers

OBJECTIVE

An interferon-gamma release assay (IGRA) is used to screen for latent tuberculosis infection (LTBI). Among IGRAs, the QuantiFERON-TB Gold In-Tube (QFT-GIT) results are highly variable, so the borderline zone has been proposed to reduce unnecessary LTBI treatment. The aim of this study was to examine the proportion of the borderline zone of QFT-GIT in healthcare workers' (HCWs) serial IGRA and to retrospectively identify the utility of predicting tuberculosis (TB) in a moderate TB incidence setting.

METHODS

The participants were HCWs who had undergone serial LTBI screening between June 2013 and June 2018. IGRA-positive HCWs underwent examinations that included low-dose computed tomography (LDCT) and TB culture, if necessary. Applying the borderline zone (0.2-<0.7 IU/mL), the results were classified as definite negative, borderline negative, borderline positive and definite positive.

RESULTS

Through the follow-up of 477 HCWs, 441 (92.5%) invariant, 30 (6.3%) conversion, 2 (0.4%) reversion and 5 (1.0%) indeterminate results were observed with the manufacturer's cutoff. Applying the borderline zone, 419 (87.8%) invariant, 22 (4.6%) conversion, 1 (0.2%) reversion and 36 (7.5%) decision pending, including 5 (1.0%) indeterminate results, were observed. At the time of screening, five TB cases were identified. Chest X-ray (CXR) identified one TB case, and LDCT identified four additional TB cases. After one year, two TB cases were diagnosed, and their screening QFT-GIT results were definite positive and borderline negative. In the Cochran-Armitage trend test, the greater the maximum difference in the QFT-GIT grade with the borderline zone was, the higher the probability of developing TB (P-value <0.001).

CONCLUSION

The application of the borderline zone lowered the conversion rate but increased the decision pending rate. Introducing the borderline zone requires a careful approach, and a thorough examination needs to be performed to rule out TB in converters. HCWs with borderline QFT-GIT results also need close observation.

Adults with Mycobacterium tuberculosis infection and pre-diabetes have increased levels of QuantiFERON interferon-gamma responses

BACKGROUND

Diabetes is associated with increased prevalence of TB infection in the US. We assessed associations between diabetes and interferon-gamma (IFN-γ) TB antigen response among adults with TB infection using US representative data.

METHODS

National Health and Nutrition Examination (NHANES) participants >19 years from 2011 to 2012 with positive QuantiFERON®-TB Gold-In-Tube (QFT) results were eligible. Diabetes was defined by combination of self-report and glycated hemoglobin (HbA1c). Quantitative IFN-γ TB antigen was classified as high (≥10 IU/mL), intermediate (1.01-9.99 IU/mL), or low (0.35-1.00 IU/mL). Analyses accounted for NHANES weighted design.

RESULTS

Among NHANES participants >19 years, n = 513 had positive QFT (5.9%). Among those with positive QFT, diabetes prevalence was 22.2% and pre-diabetes was 25.9%. Overall, 16.7% of positive QFT participants had high IFN-γ TB antigen levels including 21.7% among those with diabetes, 20.8% among those with pre-diabetes, and 12.6% among euglycemic participants. In adjusted analyses, high IFN-γ TB antigen response was more common among those with pre-diabetes (aOR 1.9, 95%CI 1.0, 3.6) compared to euglycemic participants.

CONCLUSION

Higher antigen responses may reflect immunopathy consistent with an exaggerated inflammatory but ineffectual response to TB or a reflection of more Mtb replication in participants with pre-diabetes or diabetes.

Performance Evaluation of a New Automated Chemiluminescent Immunoanalyzer-Based Interferon-Gamma Releasing Assay AdvanSure I3 in Comparison With the QuantiFERON-TB Gold In-Tube Assay

BACKGROUND

The interferon-gamma (IFN-γ) releasing assay (IGRA) is widely used for latent tuberculosis infection (LTBI) diagnosis. We evaluated the analytical performance of a new automated chemiluminescent immunoanalyzer-based IGRA (CLIA-IGRA), AdvanSure I3 (LG Life Sciences, Seoul, Korea) and compared it with that of the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay.

METHODS

Repeatability and reproducibility were evaluated at four levels. Detection capability, including limit of blank (LoB), limit of detection (LoD), and limit of quantification (LoQ), was evaluated using IFN-γ standard material (National Institute for Biological Standards and Control code: 87/586). Agreement between the results of two assays was evaluated using 341 blood samples from healthcare workers and patients at a tertiary care hospital. To determine the cut-off value of CLIA-IGRA for diagnosing LTBI, the ROC curve was analyzed.

RESULTS

Repeatability and reproducibility were 4.86-7.00% and 6.36-7.88% CV, respectively. LoB, LoD, and LoQ were 0.022, 0.077, and 0.249 IU/mL, respectively. IFN-γ values between CLIA-IGRA and QFT-GIT showed a strong correlation within the analytical measurable range of both assays, especially when the value was low. Qualitative comparison of the two assays yielded a 99.1% overall agreement (kappa coefficient=0.98). A cut-off value of 0.35 IU/mL was appropriate for diagnosing LTBI.

CONCLUSIONS

CLIA-IGRA is a reliable assay for LTBI diagnosis, with performance similar to that of QFT-GIT.

Optimization and Interpretation of Serial QuantiFERON Testing to Measure Acquisition of Mycobacterium tuberculosis Infection

RATIONALE

Conversion from a negative to positive QuantiFERON-TB test is indicative of Mycobacterium tuberculosis (Mtb) infection, which predisposes individuals to tuberculosis disease. Interpretation of serial tests is confounded by immunological and technical variability.

OBJECTIVES

To improve the consistency of serial QuantiFERON-TB testing algorithms and provide a data-driven definition of conversion.

METHODS

Sources of QuantiFERON-TB variability were assessed, and optimal procedures were identified. Distributions of IFN-γ response levels were analyzed in healthy adolescents, Mtb-unexposed control subjects, and patients with pulmonary tuberculosis.

MEASUREMENTS AND MAIN RESULTS

Individuals with no known Mtb exposure had IFN-γ values less than 0.2 IU/ml. Among individuals with IFN-γ values less than 0.2 IU/ml, 0.2-0.34 IU/ml, 0.35-0.7 IU/ml, and greater than 0.7 IU/ml, tuberculin skin test positivity results were 15%, 53%, 66%, and 91% (P < 0.005), respectively. Together, these findings suggest that values less than 0.2 IU/ml were true negatives. In short-term serial testing, "uncertain" conversions, with at least one value within the uncertainty zone (0.2-0.7 IU/ml), were partly explained by technical assay variability. Individuals who had a change in QuantiFERON-TB IFN-γ values from less than 0.2 to greater than 0.7 IU/ml had 10-fold higher tuberculosis incidence rates than those who maintained values less than 0.2 IU/ml over 2 years (P = 0.0003). By contrast, "uncertain" converters were not at higher risk than nonconverters (P = 0.229). Eighty-seven percent of patients with active tuberculosis had IFN-γ values greater than 0.7 IU/ml, suggesting that these values are consistent with established Mtb infection.

CONCLUSIONS

Implementation of optimized procedures and a more rigorous QuantiFERON-TB conversion definition (an increase from IFN-γ <0.2 to >0.7 IU/ml) would allow more definitive detection of recent Mtb infection and potentially improve identification of those more likely to develop disease.

Optimization and Interpretation of Serial QuantiFERON Testing to Measure Acquisition of Mycobacterium tuberculosis Infection

RATIONALE

Conversion from a negative to positive QuantiFERON-TB test is indicative of Mycobacterium tuberculosis (Mtb) infection, which predisposes individuals to tuberculosis disease. Interpretation of serial tests is confounded by immunological and technical variability.

OBJECTIVES

To improve the consistency of serial QuantiFERON-TB testing algorithms and provide a data-driven definition of conversion.

METHODS

Sources of QuantiFERON-TB variability were assessed, and optimal procedures were identified. Distributions of IFN-γ response levels were analyzed in healthy adolescents, Mtb-unexposed control subjects, and patients with pulmonary tuberculosis.

MEASUREMENTS AND MAIN RESULTS

Individuals with no known Mtb exposure had IFN-γ values less than 0.2 IU/ml. Among individuals with IFN-γ values less than 0.2 IU/ml, 0.2-0.34 IU/ml, 0.35-0.7 IU/ml, and greater than 0.7 IU/ml, tuberculin skin test positivity results were 15%, 53%, 66%, and 91% (P < 0.005), respectively. Together, these findings suggest that values less than 0.2 IU/ml were true negatives. In short-term serial testing, "uncertain" conversions, with at least one value within the uncertainty zone (0.2-0.7 IU/ml), were partly explained by technical assay variability. Individuals who had a change in QuantiFERON-TB IFN-γ values from less than 0.2 to greater than 0.7 IU/ml had 10-fold higher tuberculosis incidence rates than those who maintained values less than 0.2 IU/ml over 2 years (P = 0.0003). By contrast, "uncertain" converters were not at higher risk than nonconverters (P = 0.229). Eighty-seven percent of patients with active tuberculosis had IFN-γ values greater than 0.7 IU/ml, suggesting that these values are consistent with established Mtb infection.

CONCLUSIONS

Implementation of optimized procedures and a more rigorous QuantiFERON-TB conversion definition (an increase from IFN-γ <0.2 to >0.7 IU/ml) would allow more definitive detection of recent Mtb infection and potentially improve identification of those more likely to develop disease.