|Year : 2019 | Volume
| Issue : 3 | Page : 433-437
Utility of QuantiFERON®-TB gold In-Tube test compared with tuberculin skin test in diagnosing tuberculosis in Indian children with malnutrition
Deepthi Boddu1, Valsan Philip Verghese1, Joy Sarojini Michael2, Anila Chacko1, Visali Jeyaseelan3
1 Department of Paediatrics, Christian Medical College, Vellore, Tamil Nadu, India
2 Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, India
3 Department of Biostatistics, Christian Medical College, Vellore, Tamil Nadu, India
|Date of Submission||14-Jun-2019|
|Date of Decision||09-Aug-2019|
|Date of Acceptance||09-Aug-2019|
|Date of Web Publication||29-Nov-2019|
Dr. Anila Chacko
Department of Paediatrics, Unit-III, Christian Medical College, Vellore, Tamil Nadu
Source of Support: None, Conflict of Interest: None
This prospective cohort study was conducted to compare the accuracy of QuantiFERON®-TB (QFT) Gold In-Tube test and tuberculin skin test (TST) in diagnosing tuberculosis (TB) in predominantly bacille Calmette–Guerin-vaccinated children with a high incidence of malnutrition. The sensitivity of the QFT versus the TST was 69.6% versus 52.9% for WHO-defined TB, with specificity of 86% versus 78.3%, respectively. The concordance of the TST and QFT was 79% overall (κ = 0.430), 62.5% in those with WHO-defined TB and 85.7% in those without TB. Majority of the QFT+/TST − discordance was seen in children with TB, whereas majority of the TST+/QFT − discordance was seen in those without TB. The TST was more likely to be negative in children with moderate-to-severe malnutrition (P = 0.003) compared to the QFT, which was more likely to be positive in younger children. The significantly better performance of the QFT in malnourished children and those at younger ages supports its use for TB diagnosis in these subpopulations.
Keywords: Children with malnutrition, QuantiFERON-TB Gold In-Tube test, tuberculin skin test, tuberculosis diagnosis
|How to cite this article:|
Boddu D, Verghese VP, Michael JS, Chacko A, Jeyaseelan V. Utility of QuantiFERON®-TB gold In-Tube test compared with tuberculin skin test in diagnosing tuberculosis in Indian children with malnutrition. Indian J Med Microbiol 2019;37:433-7
|How to cite this URL:|
Boddu D, Verghese VP, Michael JS, Chacko A, Jeyaseelan V. Utility of QuantiFERON®-TB gold In-Tube test compared with tuberculin skin test in diagnosing tuberculosis in Indian children with malnutrition. Indian J Med Microbiol [serial online] 2019 [cited 2020 Jul 13];37:433-7. Available from: http://www.ijmm.org/text.asp?2019/37/3/433/272022
| ~ Introduction|| |
The global incidence of tuberculosis (TB) was 10 million in 2017, of whom 1 million were children. India had the highest number of incident cases in 2017, with 24% of the global incidence and the highest number of TB cases attributable to undernutrition as a risk factor. The ambiguity of the signs and symptoms of TB in children; the paucibacillary nature of childhood TB and the absence of a sensitive, specific and rapid method of diagnosis all lead to difficulty in accurately diagnosing TB in children. The traditional tuberculin skin test (TST) that measures cell-mediated response to tuberculin antigens can give false-positive results in bacille Calmette-Guerin (BCG)-vaccinated children due to antigens common between tuberculin and BCG, as well as with infections due to non-tuberculous mycobacteria (NTMs). False-negative results occur in malnourished children due to anergy. The QuantiFERON®-TB (QFT) Gold In-Tube test detects interferon-gamma (INF-γ) release from a patient's CD4+ T-lymphocytes after stimulation by antigens found on the Mycobacterium tuberculosis complex, with the advantages over the TST of no cross-reactivity with BCG vaccine and NTMs, no boosting after each test and being less impacted by immune suppression and malnutrition.
This study was conducted to compare the diagnostic accuracy of QFT and TST in identifying WHO-defined TB in children from a BCG-vaccinated population with a high incidence of malnutrition.
| ~ Materials and Methods|| |
This prospective cohort study enrolled children aged 1–15 years with symptoms or signs suggestive of TB whose parent or guardian was willing to participate in the study and provided informed consent for phlebotomy. Children with a history of having received anti-TB medication for >3 days were excluded from the study. The sample size was calculated using the following formula, n = za2 P × q/d2, where 'd2' is the precision, 'p' is the sensitivity of QFT in comparison to TST and 'q' is 1 − p. Using this formula, a sample size of 80 was estimated to be adequate.
Following informed consent, children with presumptive TB had 3 ml of blood withdrawn for QFT testing, after which the TST was administered with 1 TU (0.1 ml) of tuberculin PPD RT-23 with Tween 80. TST results were read 48 h after administration, with induration of ≥10 mm (≥5 mm in immune compromised) considered as positive. A three-tube test was used for QFT testing, with 1 ml of blood instilled into each of the tubes, namely antigen, control and mitogen. The samples were sent to the laboratory within 4 h of extraction for 24 h of incubation, and then centrifuged for serum which were analysed by an automated enzyme-linked immunosorbent assay machine. QFT was categorised as positive (>2.0 IU/ml), negative (<0.35 IU/ml) or indeterminate (0.35–2.0 IU/ml), as per the standard operating procedure of the laboratory. Reading of the results of TST and QFT was blinded, with the laboratory personnel having no access to the clinical data and the clinical team not knowing the QFT result prior to TST interpretation. AFB smear, culture and other tests for TB were done as clinically indicated, after which the children were classified into one of the three WHO-defined groups, namely confirmed TB, clinical TB or not TB.
The 2014 WHO case definition of TB was used for our study, with presumptive TB referring to a patient with symptoms or signs suggestive of TB. Confirmed TB was defined as a case from whom a biological specimen was positive for M. tuberculosis by smear microscopy, culture or WHO-endorsed rapid diagnostics (WRD). Clinical TB cases were those who did not fulfil the criteria for bacterial confirmation but were diagnosed by a clinician as active TB based on X-ray abnormalities or suggestive histology and extrapulmonary cases without laboratory confirmation. Children without clinical or confirmed TB were classified as not TB.
Protein–energy malnutrition (PEM) was defined according to the Indian Academy of Pediatrics definition, with normal nutrition defined as a weight >80% of expected weight for age by accepted national reference standards. Children were classified as Grade I PEM when their weights were 71%–80% of expected weight for age and Grade II PEM or higher with weights ≤70% of expected weight for age.
Statistical analysis was done with R Software for Windows, version 3.5.0, 2018 (The R Project for Statistical Computing, Vienna, Austria) to derive validity statistics (sensitivity, specificity and predictive values with 95% confidence interval [CI]) and agreement statistics (κ with 95% CI).
Ethical approval for the study was obtained from the Institutional Review Board of Christian Medical College, Vellore.
| ~ Results|| |
Eighty-six children with presumptive TB were recruited for the study, of whom 49 (57%) were boys and 37 (43%) were girls. Their ages ranged from 1 to 15 years, with a mean age of 7.0 ± 4.2 years at presentation. Thirty-eight children were under 5 years of age at presentation, and 48 children were 5 years or older. Eighty-five of 86 children (99%) were BCG vaccinated. Forty-eight of the 86 children (56%) were malnourished at the study entry, with 28 children (33%) having PEM Grade II or higher. Twenty-four children had WHO-defined TB (pulmonary TB 7, TB meningitis 9, spinal TB 3, lymph node TB 2, cold abscess 1, abdominal TB 1 and genitourinary TB 1). Seven of the 24 children had confirmed TB, with positive cultures in 6 (25%) and smear positivity in 3 (13%).
The TST was positive ≥10 mm in 17 (20%) of the 86 children with presumptive TB. The TST had a sensitivity of 52.9% and a specificity of 78.3% in the WHO-defined (confirmed plus clinical) TB, with a positive predictive value of 37.5% and a negative predictive value of 87.1%. Six (7%) of the 86 children had indeterminate QFT results and were excluded from the analysis of QFT results. Of the remaining 80 children, 23 (29%) were QFT positive and 57 (71%) were QFT negative. The QFT had a sensitivity of 69.6% and a specificity of 86% in the WHO-defined TB, with a positive predictive value of 66.7% and a negative predictive value of 87.5% [Table 1].
|Table 1: Accuracy of tuberculin skin test (n=86) and QuantiFERON-TB Gold In-Tube test (n=80) in children with WHO-defined tuberculosis|
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The overall concordance of TST and QFT in eighty evaluable children was 79% (κ = 0.43). The concordance of TST and QFT in children with the WHO-defined TB was 62.5% (κ = 0.31) and 85.7% (κ = 0.35) in those without TB [Table 2]. Discordance between TST and QFT was seen in 17 (21%) of the 80 children. Twelve of these children were QFT+/TST − discordant, of whom eight were with TB disease. The remaining five children were TST+/QFT − discordant, of whom four were without TB.
|Table 2: Agreement of QuantiFERON-TB Gold In-Tube test and tuberculin skin test (n=80) among various defined groups|
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Univariate analysis of TST and QFT with age, sex and nutritional status was also done [Table 3]. The QFT was more likely to be positive in younger children compared to the TST. The TST was more likely to be negative in children with malnutrition compared to the QFT, especially in those with moderate-to-severe malnutrition (Grade II PEM and above). Among the eighty children, in whom both QFT and TST testing was done (data not shown), TST was more likely to be negative among children with any degree of malnutrition compared to the QFT (odds ratio: 0.13, 95% CI: 0.03–0.50, P = 0.001).
|Table 3: Association of tuberculin skin test (n=86) and QuantiFERON-TB Gold In-Tube test (n=80) with age, sex and nutritional status in children with WHO-defined tuberculosis|
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| ~ Discussion|| |
The QFT performed better than the TST in our cohort of BCG-vaccinated children, with sensitivity and positive predictive value higher than those for the TST against all categories of TB, including both confirmed and clinical cases.
The QFT has been demonstrated to have good sensitivity, ranging from 78% through 82.6% and 93%, to up to 100%, in children with confirmed TB from countries with a low burden of TB disease and without universal BCG vaccination. When measured against all TB diseases including those without bacteriological confirmation, the sensitivity of the QFT fell, ranging from 63% to as low as 32% in South Africa and 23% in India. The TST has also shown sensitivity ranging from 90% to 100% in confirmed TB cases but lower sensitivity when clinical TB cases were included, ranging from 80% in the UK and Turkey through 62% in Taiwan to as low as 30%–35% in India and South Africa, in young children below the age of 3 years. All these studies (except one) and a meta-analysis showed a lower sensitivity of the TST in BCG-vaccinated children and in those from low-income countries as well as a higher specificity of the QFT similar to our study, indicating that INF-γ assays are better indicators of the risk of M. tuberculosis infection than TST in a BCG-vaccinated population.
In the present study, the overall concordance between QFT and TST was 79% (κ = 0.43) in the whole cohort, with the highest concordance of 85% found in children without TB disease. While most studies from countries without BCG vaccination have shown good concordance between the QFT and TST, two studies from India in BCG-vaccinated children have shown that the agreement between tests in BCG-vaccinated children was only fair, with κ = 0.23 in confirmed TB and 0.30 in all TB disease categories in young children, similar to all the groups from our study. This suggests that exchanging one test for the other is unlikely to give the same information.
The fact that majority of the TST+/QFT − discordance was in the group without TB favours a positive effect of BCG vaccination on TST positivity as evidenced elsewhere, especially with no other evidence for TB disease. A pooled analysis of two German studies reported that 85% of all TST+/QFT − discordance could be attributed to prior BCG vaccination, implying a better specificity of the QFT test. QFT+/TST − discordance being more in those with TB also tends to suggest that QFTs are more sensitive for TB in a BCG-vaccinated population.
The TST was more likely to be negative in children with moderate-to-severe malnutrition (P = 0.003), unlike the QFT. TST was more likely to be negative in children with lower weight for age and weight for height indices in previous studies from India. The QFT was also more likely to be positive in younger children, similar to studies elsewhere, and the pooled analysis of German studies which observed that nearly 50% of QFT+/TST − discordance was seen in younger individuals. While the German study included adults as well, studies focusing exclusively on children have shown that the sensitivity of QFT and TST, falls in younger children. Although immature immune responses in younger children and blunted immune responses in malnutrition could contribute to these findings, these alone cannot account for all discordances between the tests, which could also be due to poorer mitogen responses and differential activation of immune markers in children who show discordant TST/QFT responses.
A limitation of our study is the fact that the number of confirmed TB cases was less, a limitation that is seen in almost all studies on TB in children. This underlines the fact that diagnosing TB in children continues to be a challenging clinical exercise, necessitating the continued search for better diagnostic tests.
| ~ Conclusions|| |
The better performance of the QFT in malnourished children and those at younger ages would lead one to support its use in these subpopulations of children with TB. However, as a negative QFT alone does not rule out active TB, a case could be made to use both tests which would improve the sensitivity of diagnosing TB over a single test alone, as seen in the UK.
The fact that neither the QFT nor the TST can differentiate between latent TB infection and active TB disease continues to challenge researchers to look for newer tests of biomarkers that can differentiate between the two such as the novel T-cell activation marker-TB assay, which would help to provide improved diagnostics in childhood TB.
This study was supported by a Fluid Research Grant from Christian Medical College, Vellore.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]