|Year : 2020 | Volume
| Issue : 3 | Page : 37-40
Serum adenosine deaminase and tuberculin skin test in children with tuberculosis contact
Wanaporn Anuntaseree, Waroon Tangjitrapitak, Hansa Sriphongphankul, Kanokpan Ruangnapa, Kantara Saelim, Pharsai Prasertsan
Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand
|Date of Submission||29-Jun-2020|
|Date of Decision||04-Aug-2020|
|Date of Acceptance||28-Dec-2020|
|Date of Web Publication||06-May-2021|
Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla 90110
Source of Support: None, Conflict of Interest: None
Background: The tuberculin skin test (TST) is used in children who have been in contact with tuberculosis (TB). The test has limitations in terms of operator variability and the need for a second visit at 48–72 h for interpretation. Serum adenosine deaminase (ADA) was studied in adults and found to have a strong correlation with TST. Until now no data are available in the pediatric population. Objective: To examine the correlation between serum ADA and the TST in children who had been in contact with TB. Materials and Methods: A prospective study was conducted at Songklanagarind Hospital in southern Thailand among children aged 2–15 years with a history of contact TB between 2016 and 2018. Serum ADA was obtained before performing the TST. Children with active TB disease were excluded from the analysis. Results: Sixty-seven children were enrolled. The serum ADA ranged from 9.3–43 IU/L. The overall correlation between serum ADA and TST was poor (ρ = −0.03, P = 0.84). However, a subgroup analysis excluding 32 children with TST size 0 mm and a high variation of serum ADA (10–37.6 IU/L) found that in the remaining children, serum ADA and TST had a moderate correlation with statistical significance (ρ = 0.48, P = 0.004). Conclusions: The correlation between serum ADA and TST in contact TB pediatric patients was poor. The cause of low correlation was due to a high variability of serum ADA level in children who had no reaction to TST.
Keywords: Latent tuberculosis infection, serum adenosine deaminase, tuberculin skin test
|How to cite this article:|
Anuntaseree W, Tangjitrapitak W, Sriphongphankul H, Ruangnapa K, Saelim K, Prasertsan P. Serum adenosine deaminase and tuberculin skin test in children with tuberculosis contact. Pediatr Respirol Crit Care Med 2020;4:37-40
|How to cite this URL:|
Anuntaseree W, Tangjitrapitak W, Sriphongphankul H, Ruangnapa K, Saelim K, Prasertsan P. Serum adenosine deaminase and tuberculin skin test in children with tuberculosis contact. Pediatr Respirol Crit Care Med [serial online] 2020 [cited 2021 Jun 19];4:37-40. Available from: https://www.prccm.org/text.asp?2020/4/3/37/315577
| Introduction|| |
The diagnosis and treatment of latent tuberculosis infection (LTBI) are key components of tuberculosis (TB) control. Children with LTBI are at high risk of developing active TB disease within 5 years after initial infection. Contact investigation using a tuberculin skin test (TST) is the recommended method of identifying LTBI in children and adolescents. The principle mechanism of the TST is a delayed-type hypersensitivity reaction, induced by the antigenic components of Mycobacterium TB (MTB). A positive TST without evidence of active TB is defined as LTBI. Although the TST is a simple and low-material procedure, the test has some limitations, notably operator variability and the time required, as the proper reading of the TST includes measuring and recording the diameter of the area of induration in millimeters 48–72 h after TST placement. In addition, TST specificity is reduced by the bacille Calmette-Guérin (BCG) vaccination. As the test has low specificity, most positive reactions in low-risk individuals are false positives.
The interferon-gamma releasing assay (IGRA) is blood test that detects interferon-gamma released from T-lymphocytes after stimulation by MTB which has been studied as a possible alternative to the TST for the diagnosis of LTBI. A systematic review indicated that the IGRA had increased specificity for LTBI in children compared with TST, but varying sensitivities. The IGRA is also much more expensive than the TST. Although the use of IGRA has been increasing, a recent study reported no clear evidence that would justify replacing the TST with the IGRA for detecting LTBI in children.
Adenosine deaminase (ADA) is an enzyme that is involved in the metabolism of purine and catalyzes the deamination reaction from adenosine to inosine. There are two isoforms of ADA. ADA-1 is found in many tissues including red blood cells. ADA-2 is found only in macrophages and monocytes. The ADA-2 level is increased in patients with TB because of the stimulation of T-cell lymphocytes by mycobacterial antigens. The ADA assay, which detects total ADA, has been widely used for the diagnosis of TB disease in adult due to its simplicity, low cost, and quickly available results. The specificity, sensitivity, and cut-off value in various body fluids of this assay have been studied and the results showed high accuracy for the screening test. Studies in children found that the serum activity of ADA was significantly higher in patients with TB compared to those without the disease., However, these studies could not reveal any diagnostic value of serum ADA in LTBI.
Although serum ADA is widely used for the diagnosis of TB disease, the use of serum ADA for LTBI diagnosis is still lacking. Only one study has examined the correlation between serum ADA and TST for the diagnosis of LTBI in adults who had contact with TB patients, which reported an ADA cut point for LTBI diagnosis of 16 U/L with the sensitivity of 84% and specificity of 100%. This suggests the possibility of using serum ADA as a diagnostic test for LTBI instead of TST or IGRA. However, there are to date no studies in pediatric populations to test the potential use of ADA to detect LTBI. The objective of this study was to examine the correlation of serum ADA and TST in children who had contact with a TB patient.
| Materials and Methods|| |
Study setting and design
A prospective study was conducted at the pediatric outpatient clinic of Songklanagarind Hospital, Songkhla province in southern Thailand.
Study population and sample size calculation
Children aged 2–15 years who attended at pediatric outpatient clinic from November 2016 to March 2018 with a history of contact with pulmonary TB patients were recruited. Children with immunodeficiency disease, malignancy, currently using anti-TB, or immunosuppressive medications and/or who had current respiratory symptoms or fever were excluded. The sample size was calculated based on an estimated correlation coefficient of 0.5, the total number of children required in this study was 29.
Data collection and study procedures
The children's caregivers were interviewed for a detailed history of TB contact as well as symptoms suggestive of TB and a physical examination was performed on all study subjects. Blood samples were collected to measure serum ADA using the conventional method, which is a routine service in the hospital. After blood collection, a TST was performed by injection of 0.1 mL of the purified protein derivative from Mycobacterium bovine into the intradermal layer at the forearm and the size of any resulting induration was measured by a well-trained physician 48–72 h later. The largest transverse diameter was measured by a flexible ruler. Chest radiograph in the posteroanterior view was performed on all children and interpreted by a pediatric radiologist or pulmonologist.
LTBI was defined as a positive tuberculin test (TST ≥10 mm) without evidence of active TB disease (normal physical examination and chest radiography).
A child was considered to have active pulmonary TB if there were any signs or symptoms suggestive of TB with abnormal chest radiography with or without positive sputum acid-fast bacilli stained or culture for TB.
EpiData version 3.1 (Odense, Denmark) was used to develop a database of all variables. The statistical analysis was performed using the R software 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria). Continuous variables are presented as mean and standard deviation (SD) or median and interquartile range (IQR) where appropriate. As the variables are not normally distributed, then the Spearman rank correlation was used for the correlational analysis. P values below 0.05 were considered statistically significant.
This study was approved by the Ethics Committee of the Faculty of Medicine, Prince of Songkla University, Thailand. All families were clearly informed of all study procedures before signing the consent form.
| Results|| |
Baseline characteristics of the contacted cases and index cases
During the study period, 77 children with a history of contact with TB patients were screened. Four children having TB diseases and six children having respiratory symptoms were excluded. Of the remaining 67 children who were analyzed, 46.3% were male and their mean age ± SD was 85.9 ± 44 months. Forty-five children (67.2%) were exposed to TB from their relatives. All of the children received BCG vaccine at birth. Ninety-two percent of the index cases were symptomatic and 68.7% had positive sputum acid-fast bacilli [Table 1].
Tuberculin skin test and adenosine deaminase results
The TST sizes ranged from 0 to 20 mm. Thirty-two patients (47.8%) had TST size 0 mm and 11 (16.4%) had a size deemed to indicate LTBI (TST size ≥10 mm). The serum ADA ranged from 9.3 to 43 IU/L, median 20.7 (IQR 17.4, 27.4).
The correlation between serum adenosine deaminase and tuberculin skin test
Spearman correlation indicated a poor correlation between serum ADA and TST (ρ = −0.03, P = 0.84) [Figure 1]. The 32 children with TST size 0 mm had a high variation of serum ADA (10–37.6 IU/L). We performed subgroup analysis by excluding these children. The result of the analysis on the remaining 35 children found that serum ADA and TST had a moderate correlation with statistical significance (ρ =0.48, P = 0.004) [Figure 2].
|Figure 1: The overall correlation between serum adenosine deaminase and tuberculin skin test (n = 67).|
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|Figure 2: The correlation between serum adenosine deaminase and tuberculin skin test excluding children with tuberculin skin test size 0 mm (n = 35).|
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| Discussion|| |
Our study in children who had been in contact with TB had three main findings. First, the overall correlation between serum ADA and TST was poor. Second, 47.8% of the children had no reaction with TST but had a high variation of serum ADA levels that ranged from 10 to 37.6 IU/L. Third, the subgroup correlation analysis, excluding children who had no reaction with TST, found that serum ADA and TST had a moderate correlation with statistical significance. The results of the study indicate that the factor that decreased the overall correlation between serum ADA and TST is children who had no reaction with TST.
The finding of poor overall correlation of serum ADA and TST in this study is different from a previous study in adults which found good correlation with high sensitivity and specificity. The author of that study suggested that a serum ADA of ≥16 IU/L is a strong predictor for a positive TST which can be used to diagnose LTBI. However, our findings in children do not support the use of serum ADA instead of TST.
The point of interest in this study is the finding of a high variation of serum ADA in children who had no reaction to the TST. The possible causations could be explained in terms of factors affecting the TST and factors affecting serum ADA. For the factors affecting TST, the causes of the absence of a reaction to a TST can be classified into two categories. First are children who have never been exposed to MTB or who have a recent TB infection within 6–8 weeks of exposure. Second are false-negative results due to various reasons including age younger than 2 years, the presence of viral or bacterial infections, severe malnutrition, having diseases affecting lymphoid organs, and immunosuppressive drug use. In our study, we excluded children who had conditions that could cause false-negative results from the study, so the remaining possibility is the first category, children who have never been exposed to MTB or who have a recent TB infection. However, we could not distinguish between these two conditions definitely, because we did not perform a follow-up TST to determine the tuberculin conversion.
For the factors affecting serum ADA, an increase in ADA activity can be seen in diseases associated with cellular system stimulation, such as viral infection, typhoid fever, infectious mononucleosis, liver disease, and malignancies. In our study, we excluded sick children from the study recruitment, leaving the question of whether the increased serum ADA could be the result of TB infection.
When considering the negative TST together with high serum ADA, we arrived at a new hypothesis: Is it possible that serum ADA may be more sensitive and respond earlier to MTB exposure than TST in the pediatric population? There is some supporting evidence for this idea. In our study, we found that 65.7% of the index cases were during the first 2 weeks of treatment which could imply that the child has recently exposure. Furthermore, we found a moderate correlation between serum ADA and children who reacted to the TST. Hence, it is possible that serum ADA could be one of the markers of TB infection. Nevertheless, in our study, we could not definitely prove such a hypothesis. To prove that the serum ADA is more sensitive to MTB exposure than TST is challenging. Further studies with more comprehensive designs should be performed. Other screening tests such as IGRA are needed to identify the child with LTBI. Moreover, as the level of MTB exposure (the closeness and duration of exposure) is an important factor promoting airborne transmission, this should be used to test the hypothesis. If serum ADA is a better marker of TB infection than the TST, serum ADA should be correlated with the level of exposure to MTB. To test this, more extensive data collection for the levels of exposure is needed.
Our study had some limitations. First, we did not collect data on some factors associated with TST and ADA, such as recent live vaccinations which could have interfered with the results. Another limitation is that although diseases associated with high serum levels of ADA were excluded from the study, the exclusions were based on clinical manifestations which could have been missed in asymptomatic cases. In future studies, specific diagnostic tests should be performed to prevent this problem.
| Conclusions|| |
We observed a poor correlation between serum ADA and TST results in a pediatric population. These results indicate that serum ADA cannot replace the TST for the screening of LTBI in children. Further studies are needed to examine the hypothesis that serum ADA in the pediatric population is more sensitive to MTB exposure.
Financial support and sponsorship
This work was supported by the Faculty of Medicine, Prince of Songkla University, Thailand.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]